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1 //===- TailRecursionElimination.cpp - Eliminate Tail Calls ----------------===//
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2 //
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3 // The LLVM Compiler Infrastructure
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4 //
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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5 // This file is distributed under the University of Illinois Open Source
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6 // License. See LICENSE.TXT for details.
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7 //
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8 //===----------------------------------------------------------------------===//
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9 //
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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10 // This file transforms calls of the current function (self recursion) followed
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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11 // by a return instruction with a branch to the entry of the function, creating
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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12 // a loop. This pass also implements the following extensions to the basic
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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13 // algorithm:
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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14 //
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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15 // 1. Trivial instructions between the call and return do not prevent the
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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16 // transformation from taking place, though currently the analysis cannot
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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17 // support moving any really useful instructions (only dead ones).
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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18 // 2. This pass transforms functions that are prevented from being tail
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19 // recursive by an associative and commutative expression to use an
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20 // accumulator variable, thus compiling the typical naive factorial or
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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21 // 'fib' implementation into efficient code.
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22 // 3. TRE is performed if the function returns void, if the return
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23 // returns the result returned by the call, or if the function returns a
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24 // run-time constant on all exits from the function. It is possible, though
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25 // unlikely, that the return returns something else (like constant 0), and
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26 // can still be TRE'd. It can be TRE'd if ALL OTHER return instructions in
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27 // the function return the exact same value.
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28 // 4. If it can prove that callees do not access their caller stack frame,
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29 // they are marked as eligible for tail call elimination (by the code
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30 // generator).
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31 //
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32 // There are several improvements that could be made:
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33 //
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34 // 1. If the function has any alloca instructions, these instructions will be
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35 // moved out of the entry block of the function, causing them to be
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36 // evaluated each time through the tail recursion. Safely keeping allocas
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37 // in the entry block requires analysis to proves that the tail-called
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38 // function does not read or write the stack object.
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39 // 2. Tail recursion is only performed if the call immediately precedes the
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40 // return instruction. It's possible that there could be a jump between
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41 // the call and the return.
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42 // 3. There can be intervening operations between the call and the return that
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43 // prevent the TRE from occurring. For example, there could be GEP's and
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44 // stores to memory that will not be read or written by the call. This
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45 // requires some substantial analysis (such as with DSA) to prove safe to
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46 // move ahead of the call, but doing so could allow many more TREs to be
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47 // performed, for example in TreeAdd/TreeAlloc from the treeadd benchmark.
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48 // 4. The algorithm we use to detect if callees access their caller stack
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49 // frames is very primitive.
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50 //
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51 //===----------------------------------------------------------------------===//
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52
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53 #include "llvm/Transforms/Scalar.h"
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54 #include "llvm/ADT/STLExtras.h"
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55 #include "llvm/ADT/SmallPtrSet.h"
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56 #include "llvm/ADT/Statistic.h"
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57 #include "llvm/Analysis/CaptureTracking.h"
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77
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58 #include "llvm/Analysis/CFG.h"
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59 #include "llvm/Analysis/InlineCost.h"
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60 #include "llvm/Analysis/InstructionSimplify.h"
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61 #include "llvm/Analysis/Loads.h"
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62 #include "llvm/Analysis/TargetTransformInfo.h"
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77
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63 #include "llvm/IR/CFG.h"
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|
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64 #include "llvm/IR/CallSite.h"
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65 #include "llvm/IR/Constants.h"
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83
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66 #include "llvm/IR/DataLayout.h"
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67 #include "llvm/IR/DerivedTypes.h"
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77
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68 #include "llvm/IR/DiagnosticInfo.h"
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69 #include "llvm/IR/Function.h"
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70 #include "llvm/IR/Instructions.h"
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71 #include "llvm/IR/IntrinsicInst.h"
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72 #include "llvm/IR/Module.h"
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77
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73 #include "llvm/IR/ValueHandle.h"
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74 #include "llvm/Pass.h"
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75 #include "llvm/Support/Debug.h"
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76 #include "llvm/Support/raw_ostream.h"
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77 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
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78 #include "llvm/Transforms/Utils/Local.h"
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79 using namespace llvm;
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80
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77
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81 #define DEBUG_TYPE "tailcallelim"
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82
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83 STATISTIC(NumEliminated, "Number of tail calls removed");
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84 STATISTIC(NumRetDuped, "Number of return duplicated");
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85 STATISTIC(NumAccumAdded, "Number of accumulators introduced");
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86
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87 namespace {
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88 struct TailCallElim : public FunctionPass {
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89 const TargetTransformInfo *TTI;
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83
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90 const DataLayout *DL;
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91
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92 static char ID; // Pass identification, replacement for typeid
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93 TailCallElim() : FunctionPass(ID) {
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94 initializeTailCallElimPass(*PassRegistry::getPassRegistry());
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95 }
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96
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77
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97 void getAnalysisUsage(AnalysisUsage &AU) const override;
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98
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77
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99 bool runOnFunction(Function &F) override;
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100
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101 private:
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77
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102 bool runTRE(Function &F);
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103 bool markTails(Function &F, bool &AllCallsAreTailCalls);
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104
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105 CallInst *FindTRECandidate(Instruction *I,
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106 bool CannotTailCallElimCallsMarkedTail);
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107 bool EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret,
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108 BasicBlock *&OldEntry,
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109 bool &TailCallsAreMarkedTail,
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110 SmallVectorImpl<PHINode *> &ArgumentPHIs,
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111 bool CannotTailCallElimCallsMarkedTail);
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112 bool FoldReturnAndProcessPred(BasicBlock *BB,
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113 ReturnInst *Ret, BasicBlock *&OldEntry,
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114 bool &TailCallsAreMarkedTail,
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115 SmallVectorImpl<PHINode *> &ArgumentPHIs,
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116 bool CannotTailCallElimCallsMarkedTail);
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117 bool ProcessReturningBlock(ReturnInst *RI, BasicBlock *&OldEntry,
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118 bool &TailCallsAreMarkedTail,
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119 SmallVectorImpl<PHINode *> &ArgumentPHIs,
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120 bool CannotTailCallElimCallsMarkedTail);
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121 bool CanMoveAboveCall(Instruction *I, CallInst *CI);
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122 Value *CanTransformAccumulatorRecursion(Instruction *I, CallInst *CI);
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123 };
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124 }
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125
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126 char TailCallElim::ID = 0;
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127 INITIALIZE_PASS_BEGIN(TailCallElim, "tailcallelim",
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128 "Tail Call Elimination", false, false)
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83
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129 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
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130 INITIALIZE_PASS_END(TailCallElim, "tailcallelim",
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131 "Tail Call Elimination", false, false)
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132
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133 // Public interface to the TailCallElimination pass
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134 FunctionPass *llvm::createTailCallEliminationPass() {
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135 return new TailCallElim();
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136 }
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137
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138 void TailCallElim::getAnalysisUsage(AnalysisUsage &AU) const {
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83
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139 AU.addRequired<TargetTransformInfoWrapperPass>();
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140 }
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141
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77
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142 /// \brief Scan the specified function for alloca instructions.
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143 /// If it contains any dynamic allocas, returns false.
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|
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144 static bool CanTRE(Function &F) {
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145 // Because of PR962, we don't TRE dynamic allocas.
|
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146 for (auto &BB : F) {
|
|
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147 for (auto &I : BB) {
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148 if (AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
|
|
|
149 if (!AI->isStaticAlloca())
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150 return false;
|
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151 }
|
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152 }
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153 }
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154
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77
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155 return true;
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|
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156 }
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157
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158 bool TailCallElim::runOnFunction(Function &F) {
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|
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159 if (skipOptnoneFunction(F))
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160 return false;
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161
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83
|
162 DL = F.getParent()->getDataLayout();
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163
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77
|
164 bool AllCallsAreTailCalls = false;
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165 bool Modified = markTails(F, AllCallsAreTailCalls);
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166 if (AllCallsAreTailCalls)
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167 Modified |= runTRE(F);
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168 return Modified;
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169 }
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170
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
171 namespace {
|
|
77
|
172 struct AllocaDerivedValueTracker {
|
|
|
173 // Start at a root value and walk its use-def chain to mark calls that use the
|
|
|
174 // value or a derived value in AllocaUsers, and places where it may escape in
|
|
|
175 // EscapePoints.
|
|
|
176 void walk(Value *Root) {
|
|
|
177 SmallVector<Use *, 32> Worklist;
|
|
|
178 SmallPtrSet<Use *, 32> Visited;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
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|
179
|
|
77
|
180 auto AddUsesToWorklist = [&](Value *V) {
|
|
|
181 for (auto &U : V->uses()) {
|
|
83
|
182 if (!Visited.insert(&U).second)
|
|
77
|
183 continue;
|
|
|
184 Worklist.push_back(&U);
|
|
|
185 }
|
|
|
186 };
|
|
|
187
|
|
|
188 AddUsesToWorklist(Root);
|
|
|
189
|
|
|
190 while (!Worklist.empty()) {
|
|
|
191 Use *U = Worklist.pop_back_val();
|
|
|
192 Instruction *I = cast<Instruction>(U->getUser());
|
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parents:
diff
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|
193
|
|
77
|
194 switch (I->getOpcode()) {
|
|
|
195 case Instruction::Call:
|
|
|
196 case Instruction::Invoke: {
|
|
|
197 CallSite CS(I);
|
|
|
198 bool IsNocapture = !CS.isCallee(U) &&
|
|
|
199 CS.doesNotCapture(CS.getArgumentNo(U));
|
|
|
200 callUsesLocalStack(CS, IsNocapture);
|
|
|
201 if (IsNocapture) {
|
|
|
202 // If the alloca-derived argument is passed in as nocapture, then it
|
|
|
203 // can't propagate to the call's return. That would be capturing.
|
|
|
204 continue;
|
|
|
205 }
|
|
|
206 break;
|
|
|
207 }
|
|
|
208 case Instruction::Load: {
|
|
|
209 // The result of a load is not alloca-derived (unless an alloca has
|
|
|
210 // otherwise escaped, but this is a local analysis).
|
|
|
211 continue;
|
|
|
212 }
|
|
|
213 case Instruction::Store: {
|
|
|
214 if (U->getOperandNo() == 0)
|
|
|
215 EscapePoints.insert(I);
|
|
|
216 continue; // Stores have no users to analyze.
|
|
|
217 }
|
|
|
218 case Instruction::BitCast:
|
|
|
219 case Instruction::GetElementPtr:
|
|
|
220 case Instruction::PHI:
|
|
|
221 case Instruction::Select:
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|
|
222 case Instruction::AddrSpaceCast:
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|
|
223 break;
|
|
|
224 default:
|
|
|
225 EscapePoints.insert(I);
|
|
|
226 break;
|
|
|
227 }
|
|
|
228
|
|
|
229 AddUsesToWorklist(I);
|
|
|
230 }
|
|
|
231 }
|
|
|
232
|
|
|
233 void callUsesLocalStack(CallSite CS, bool IsNocapture) {
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|
234 // Add it to the list of alloca users.
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|
|
235 AllocaUsers.insert(CS.getInstruction());
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236
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|
237 // If it's nocapture then it can't capture this alloca.
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|
238 if (IsNocapture)
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|
239 return;
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|
240
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|
|
241 // If it can write to memory, it can leak the alloca value.
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|
242 if (!CS.onlyReadsMemory())
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|
|
243 EscapePoints.insert(CS.getInstruction());
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|
|
244 }
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|
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245
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|
246 SmallPtrSet<Instruction *, 32> AllocaUsers;
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|
247 SmallPtrSet<Instruction *, 32> EscapePoints;
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|
248 };
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|
|
249 }
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|
|
250
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|
|
251 bool TailCallElim::markTails(Function &F, bool &AllCallsAreTailCalls) {
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|
|
252 if (F.callsFunctionThatReturnsTwice())
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253 return false;
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|
254 AllCallsAreTailCalls = true;
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|
255
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|
256 // The local stack holds all alloca instructions and all byval arguments.
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|
257 AllocaDerivedValueTracker Tracker;
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|
|
258 for (Argument &Arg : F.args()) {
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|
|
259 if (Arg.hasByValAttr())
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|
|
260 Tracker.walk(&Arg);
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|
|
261 }
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|
|
262 for (auto &BB : F) {
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|
|
263 for (auto &I : BB)
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|
|
264 if (AllocaInst *AI = dyn_cast<AllocaInst>(&I))
|
|
|
265 Tracker.walk(AI);
|
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
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changeset
|
266 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
267
|
|
77
|
268 bool Modified = false;
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|
|
269
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|
270 // Track whether a block is reachable after an alloca has escaped. Blocks that
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|
|
271 // contain the escaping instruction will be marked as being visited without an
|
|
|
272 // escaped alloca, since that is how the block began.
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|
|
273 enum VisitType {
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|
274 UNVISITED,
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|
|
275 UNESCAPED,
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|
|
276 ESCAPED
|
|
|
277 };
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|
|
278 DenseMap<BasicBlock *, VisitType> Visited;
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|
|
279
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|
|
280 // We propagate the fact that an alloca has escaped from block to successor.
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|
281 // Visit the blocks that are propagating the escapedness first. To do this, we
|
|
|
282 // maintain two worklists.
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|
|
283 SmallVector<BasicBlock *, 32> WorklistUnescaped, WorklistEscaped;
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|
|
284
|
|
|
285 // We may enter a block and visit it thinking that no alloca has escaped yet,
|
|
|
286 // then see an escape point and go back around a loop edge and come back to
|
|
|
287 // the same block twice. Because of this, we defer setting tail on calls when
|
|
|
288 // we first encounter them in a block. Every entry in this list does not
|
|
|
289 // statically use an alloca via use-def chain analysis, but may find an alloca
|
|
|
290 // through other means if the block turns out to be reachable after an escape
|
|
|
291 // point.
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|
|
292 SmallVector<CallInst *, 32> DeferredTails;
|
|
|
293
|
|
|
294 BasicBlock *BB = &F.getEntryBlock();
|
|
|
295 VisitType Escaped = UNESCAPED;
|
|
|
296 do {
|
|
|
297 for (auto &I : *BB) {
|
|
|
298 if (Tracker.EscapePoints.count(&I))
|
|
|
299 Escaped = ESCAPED;
|
|
|
300
|
|
|
301 CallInst *CI = dyn_cast<CallInst>(&I);
|
|
|
302 if (!CI || CI->isTailCall())
|
|
|
303 continue;
|
|
|
304
|
|
|
305 if (CI->doesNotAccessMemory()) {
|
|
|
306 // A call to a readnone function whose arguments are all things computed
|
|
|
307 // outside this function can be marked tail. Even if you stored the
|
|
|
308 // alloca address into a global, a readnone function can't load the
|
|
|
309 // global anyhow.
|
|
|
310 //
|
|
|
311 // Note that this runs whether we know an alloca has escaped or not. If
|
|
|
312 // it has, then we can't trust Tracker.AllocaUsers to be accurate.
|
|
|
313 bool SafeToTail = true;
|
|
|
314 for (auto &Arg : CI->arg_operands()) {
|
|
|
315 if (isa<Constant>(Arg.getUser()))
|
|
|
316 continue;
|
|
|
317 if (Argument *A = dyn_cast<Argument>(Arg.getUser()))
|
|
|
318 if (!A->hasByValAttr())
|
|
|
319 continue;
|
|
|
320 SafeToTail = false;
|
|
|
321 break;
|
|
|
322 }
|
|
|
323 if (SafeToTail) {
|
|
|
324 emitOptimizationRemark(
|
|
|
325 F.getContext(), "tailcallelim", F, CI->getDebugLoc(),
|
|
|
326 "marked this readnone call a tail call candidate");
|
|
|
327 CI->setTailCall();
|
|
|
328 Modified = true;
|
|
|
329 continue;
|
|
|
330 }
|
|
|
331 }
|
|
|
332
|
|
|
333 if (Escaped == UNESCAPED && !Tracker.AllocaUsers.count(CI)) {
|
|
|
334 DeferredTails.push_back(CI);
|
|
|
335 } else {
|
|
|
336 AllCallsAreTailCalls = false;
|
|
|
337 }
|
|
|
338 }
|
|
|
339
|
|
|
340 for (auto *SuccBB : make_range(succ_begin(BB), succ_end(BB))) {
|
|
|
341 auto &State = Visited[SuccBB];
|
|
|
342 if (State < Escaped) {
|
|
|
343 State = Escaped;
|
|
|
344 if (State == ESCAPED)
|
|
|
345 WorklistEscaped.push_back(SuccBB);
|
|
|
346 else
|
|
|
347 WorklistUnescaped.push_back(SuccBB);
|
|
|
348 }
|
|
|
349 }
|
|
|
350
|
|
|
351 if (!WorklistEscaped.empty()) {
|
|
|
352 BB = WorklistEscaped.pop_back_val();
|
|
|
353 Escaped = ESCAPED;
|
|
|
354 } else {
|
|
|
355 BB = nullptr;
|
|
|
356 while (!WorklistUnescaped.empty()) {
|
|
|
357 auto *NextBB = WorklistUnescaped.pop_back_val();
|
|
|
358 if (Visited[NextBB] == UNESCAPED) {
|
|
|
359 BB = NextBB;
|
|
|
360 Escaped = UNESCAPED;
|
|
|
361 break;
|
|
|
362 }
|
|
|
363 }
|
|
|
364 }
|
|
|
365 } while (BB);
|
|
|
366
|
|
|
367 for (CallInst *CI : DeferredTails) {
|
|
|
368 if (Visited[CI->getParent()] != ESCAPED) {
|
|
|
369 // If the escape point was part way through the block, calls after the
|
|
|
370 // escape point wouldn't have been put into DeferredTails.
|
|
|
371 emitOptimizationRemark(F.getContext(), "tailcallelim", F,
|
|
|
372 CI->getDebugLoc(),
|
|
|
373 "marked this call a tail call candidate");
|
|
|
374 CI->setTailCall();
|
|
|
375 Modified = true;
|
|
|
376 } else {
|
|
|
377 AllCallsAreTailCalls = false;
|
|
|
378 }
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
379 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
380
|
|
77
|
381 return Modified;
|
|
|
382 }
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
383
|
|
77
|
384 bool TailCallElim::runTRE(Function &F) {
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
385 // If this function is a varargs function, we won't be able to PHI the args
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
386 // right, so don't even try to convert it...
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
387 if (F.getFunctionType()->isVarArg()) return false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
388
|
|
83
|
389 TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
|
|
77
|
390 BasicBlock *OldEntry = nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
391 bool TailCallsAreMarkedTail = false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
392 SmallVector<PHINode*, 8> ArgumentPHIs;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
393 bool MadeChange = false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
394
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
395 // CanTRETailMarkedCall - If false, we cannot perform TRE on tail calls
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
396 // marked with the 'tail' attribute, because doing so would cause the stack
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
397 // size to increase (real TRE would deallocate variable sized allocas, TRE
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
398 // doesn't).
|
|
77
|
399 bool CanTRETailMarkedCall = CanTRE(F);
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
400
|
|
77
|
401 // Change any tail recursive calls to loops.
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
402 //
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
403 // FIXME: The code generator produces really bad code when an 'escaping
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
404 // alloca' is changed from being a static alloca to being a dynamic alloca.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
405 // Until this is resolved, disable this transformation if that would ever
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
406 // happen. This bug is PR962.
|
|
83
|
407 SmallVector<BasicBlock*, 8> BBToErase;
|
|
77
|
408 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
|
|
|
409 if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) {
|
|
|
410 bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
|
|
|
411 ArgumentPHIs, !CanTRETailMarkedCall);
|
|
83
|
412 if (!Change && BB->getFirstNonPHIOrDbg() == Ret) {
|
|
77
|
413 Change = FoldReturnAndProcessPred(BB, Ret, OldEntry,
|
|
|
414 TailCallsAreMarkedTail, ArgumentPHIs,
|
|
|
415 !CanTRETailMarkedCall);
|
|
83
|
416 // FoldReturnAndProcessPred may have emptied some BB. Remember to
|
|
|
417 // erase them.
|
|
|
418 if (Change && BB->empty())
|
|
|
419 BBToErase.push_back(BB);
|
|
|
420
|
|
|
421 }
|
|
77
|
422 MadeChange |= Change;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
423 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
424 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
425
|
|
83
|
426 for (auto BB: BBToErase)
|
|
|
427 BB->eraseFromParent();
|
|
|
428
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
429 // If we eliminated any tail recursions, it's possible that we inserted some
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
430 // silly PHI nodes which just merge an initial value (the incoming operand)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
431 // with themselves. Check to see if we did and clean up our mess if so. This
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
432 // occurs when a function passes an argument straight through to its tail
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
433 // call.
|
|
77
|
434 for (unsigned i = 0, e = ArgumentPHIs.size(); i != e; ++i) {
|
|
|
435 PHINode *PN = ArgumentPHIs[i];
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
436
|
|
77
|
437 // If the PHI Node is a dynamic constant, replace it with the value it is.
|
|
|
438 if (Value *PNV = SimplifyInstruction(PN)) {
|
|
|
439 PN->replaceAllUsesWith(PNV);
|
|
|
440 PN->eraseFromParent();
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
441 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
442 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
443
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
444 return MadeChange;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
445 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
446
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
447
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
448 /// CanMoveAboveCall - Return true if it is safe to move the specified
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
449 /// instruction from after the call to before the call, assuming that all
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
450 /// instructions between the call and this instruction are movable.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
451 ///
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
452 bool TailCallElim::CanMoveAboveCall(Instruction *I, CallInst *CI) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
453 // FIXME: We can move load/store/call/free instructions above the call if the
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
454 // call does not mod/ref the memory location being processed.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
455 if (I->mayHaveSideEffects()) // This also handles volatile loads.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
456 return false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
457
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
458 if (LoadInst *L = dyn_cast<LoadInst>(I)) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
459 // Loads may always be moved above calls without side effects.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
460 if (CI->mayHaveSideEffects()) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
461 // Non-volatile loads may be moved above a call with side effects if it
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
462 // does not write to memory and the load provably won't trap.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
463 // FIXME: Writes to memory only matter if they may alias the pointer
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
464 // being loaded from.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
465 if (CI->mayWriteToMemory() ||
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
466 !isSafeToLoadUnconditionally(L->getPointerOperand(), L,
|
|
83
|
467 L->getAlignment(), DL))
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
468 return false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
469 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
470 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
471
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
472 // Otherwise, if this is a side-effect free instruction, check to make sure
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
473 // that it does not use the return value of the call. If it doesn't use the
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
474 // return value of the call, it must only use things that are defined before
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
475 // the call, or movable instructions between the call and the instruction
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
476 // itself.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
477 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
478 if (I->getOperand(i) == CI)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
479 return false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
480 return true;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
481 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
482
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
483 // isDynamicConstant - Return true if the specified value is the same when the
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
484 // return would exit as it was when the initial iteration of the recursive
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
485 // function was executed.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
486 //
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
487 // We currently handle static constants and arguments that are not modified as
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
488 // part of the recursion.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
489 //
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
490 static bool isDynamicConstant(Value *V, CallInst *CI, ReturnInst *RI) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
491 if (isa<Constant>(V)) return true; // Static constants are always dyn consts
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
492
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
493 // Check to see if this is an immutable argument, if so, the value
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
494 // will be available to initialize the accumulator.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
495 if (Argument *Arg = dyn_cast<Argument>(V)) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
496 // Figure out which argument number this is...
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
497 unsigned ArgNo = 0;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
498 Function *F = CI->getParent()->getParent();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
499 for (Function::arg_iterator AI = F->arg_begin(); &*AI != Arg; ++AI)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
500 ++ArgNo;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
501
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
502 // If we are passing this argument into call as the corresponding
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
503 // argument operand, then the argument is dynamically constant.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
504 // Otherwise, we cannot transform this function safely.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
505 if (CI->getArgOperand(ArgNo) == Arg)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
506 return true;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
507 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
508
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
509 // Switch cases are always constant integers. If the value is being switched
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
510 // on and the return is only reachable from one of its cases, it's
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
511 // effectively constant.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
512 if (BasicBlock *UniquePred = RI->getParent()->getUniquePredecessor())
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
513 if (SwitchInst *SI = dyn_cast<SwitchInst>(UniquePred->getTerminator()))
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
514 if (SI->getCondition() == V)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
515 return SI->getDefaultDest() != RI->getParent();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
516
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
517 // Not a constant or immutable argument, we can't safely transform.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
518 return false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
519 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
520
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
521 // getCommonReturnValue - Check to see if the function containing the specified
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
522 // tail call consistently returns the same runtime-constant value at all exit
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
523 // points except for IgnoreRI. If so, return the returned value.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
524 //
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
525 static Value *getCommonReturnValue(ReturnInst *IgnoreRI, CallInst *CI) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
526 Function *F = CI->getParent()->getParent();
|
|
77
|
527 Value *ReturnedValue = nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
528
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
529 for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
530 ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator());
|
|
77
|
531 if (RI == nullptr || RI == IgnoreRI) continue;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
532
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
533 // We can only perform this transformation if the value returned is
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
534 // evaluatable at the start of the initial invocation of the function,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
535 // instead of at the end of the evaluation.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
536 //
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
537 Value *RetOp = RI->getOperand(0);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
538 if (!isDynamicConstant(RetOp, CI, RI))
|
|
77
|
539 return nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
540
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
541 if (ReturnedValue && RetOp != ReturnedValue)
|
|
77
|
542 return nullptr; // Cannot transform if differing values are returned.
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
543 ReturnedValue = RetOp;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
544 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
545 return ReturnedValue;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
546 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
547
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
548 /// CanTransformAccumulatorRecursion - If the specified instruction can be
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
549 /// transformed using accumulator recursion elimination, return the constant
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
550 /// which is the start of the accumulator value. Otherwise return null.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
551 ///
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
552 Value *TailCallElim::CanTransformAccumulatorRecursion(Instruction *I,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
553 CallInst *CI) {
|
|
77
|
554 if (!I->isAssociative() || !I->isCommutative()) return nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
555 assert(I->getNumOperands() == 2 &&
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
556 "Associative/commutative operations should have 2 args!");
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
557
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
558 // Exactly one operand should be the result of the call instruction.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
559 if ((I->getOperand(0) == CI && I->getOperand(1) == CI) ||
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
560 (I->getOperand(0) != CI && I->getOperand(1) != CI))
|
|
77
|
561 return nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
562
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
563 // The only user of this instruction we allow is a single return instruction.
|
|
77
|
564 if (!I->hasOneUse() || !isa<ReturnInst>(I->user_back()))
|
|
|
565 return nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
566
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
567 // Ok, now we have to check all of the other return instructions in this
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
568 // function. If they return non-constants or differing values, then we cannot
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
569 // transform the function safely.
|
|
77
|
570 return getCommonReturnValue(cast<ReturnInst>(I->user_back()), CI);
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
571 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
572
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
573 static Instruction *FirstNonDbg(BasicBlock::iterator I) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
574 while (isa<DbgInfoIntrinsic>(I))
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
575 ++I;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
576 return &*I;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
577 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
578
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
579 CallInst*
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
580 TailCallElim::FindTRECandidate(Instruction *TI,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
581 bool CannotTailCallElimCallsMarkedTail) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
582 BasicBlock *BB = TI->getParent();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
583 Function *F = BB->getParent();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
584
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
585 if (&BB->front() == TI) // Make sure there is something before the terminator.
|
|
77
|
586 return nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
587
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
588 // Scan backwards from the return, checking to see if there is a tail call in
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
589 // this block. If so, set CI to it.
|
|
77
|
590 CallInst *CI = nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
591 BasicBlock::iterator BBI = TI;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
592 while (true) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
593 CI = dyn_cast<CallInst>(BBI);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
594 if (CI && CI->getCalledFunction() == F)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
595 break;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
596
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
597 if (BBI == BB->begin())
|
|
77
|
598 return nullptr; // Didn't find a potential tail call.
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
599 --BBI;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
600 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
601
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
602 // If this call is marked as a tail call, and if there are dynamic allocas in
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
603 // the function, we cannot perform this optimization.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
604 if (CI->isTailCall() && CannotTailCallElimCallsMarkedTail)
|
|
77
|
605 return nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
606
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
607 // As a special case, detect code like this:
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
608 // double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
609 // and disable this xform in this case, because the code generator will
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
610 // lower the call to fabs into inline code.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
611 if (BB == &F->getEntryBlock() &&
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
612 FirstNonDbg(BB->front()) == CI &&
|
|
77
|
613 FirstNonDbg(std::next(BB->begin())) == TI &&
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
614 CI->getCalledFunction() &&
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
615 !TTI->isLoweredToCall(CI->getCalledFunction())) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
616 // A single-block function with just a call and a return. Check that
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
617 // the arguments match.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
618 CallSite::arg_iterator I = CallSite(CI).arg_begin(),
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
619 E = CallSite(CI).arg_end();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
620 Function::arg_iterator FI = F->arg_begin(),
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
621 FE = F->arg_end();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
622 for (; I != E && FI != FE; ++I, ++FI)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
623 if (*I != &*FI) break;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
624 if (I == E && FI == FE)
|
|
77
|
625 return nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
626 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
627
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
628 return CI;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
629 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
630
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
631 bool TailCallElim::EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
632 BasicBlock *&OldEntry,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
633 bool &TailCallsAreMarkedTail,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
634 SmallVectorImpl<PHINode *> &ArgumentPHIs,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
635 bool CannotTailCallElimCallsMarkedTail) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
636 // If we are introducing accumulator recursion to eliminate operations after
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
637 // the call instruction that are both associative and commutative, the initial
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
638 // value for the accumulator is placed in this variable. If this value is set
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
639 // then we actually perform accumulator recursion elimination instead of
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
640 // simple tail recursion elimination. If the operation is an LLVM instruction
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
641 // (eg: "add") then it is recorded in AccumulatorRecursionInstr. If not, then
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
642 // we are handling the case when the return instruction returns a constant C
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
643 // which is different to the constant returned by other return instructions
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
644 // (which is recorded in AccumulatorRecursionEliminationInitVal). This is a
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
645 // special case of accumulator recursion, the operation being "return C".
|
|
77
|
646 Value *AccumulatorRecursionEliminationInitVal = nullptr;
|
|
|
647 Instruction *AccumulatorRecursionInstr = nullptr;
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
648
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
649 // Ok, we found a potential tail call. We can currently only transform the
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
650 // tail call if all of the instructions between the call and the return are
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
651 // movable to above the call itself, leaving the call next to the return.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
652 // Check that this is the case now.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
653 BasicBlock::iterator BBI = CI;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
654 for (++BBI; &*BBI != Ret; ++BBI) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
655 if (CanMoveAboveCall(BBI, CI)) continue;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
656
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
657 // If we can't move the instruction above the call, it might be because it
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
658 // is an associative and commutative operation that could be transformed
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
659 // using accumulator recursion elimination. Check to see if this is the
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
660 // case, and if so, remember the initial accumulator value for later.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
661 if ((AccumulatorRecursionEliminationInitVal =
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
662 CanTransformAccumulatorRecursion(BBI, CI))) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
663 // Yes, this is accumulator recursion. Remember which instruction
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
664 // accumulates.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
665 AccumulatorRecursionInstr = BBI;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
666 } else {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
667 return false; // Otherwise, we cannot eliminate the tail recursion!
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
668 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
669 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
670
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
671 // We can only transform call/return pairs that either ignore the return value
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
672 // of the call and return void, ignore the value of the call and return a
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
673 // constant, return the value returned by the tail call, or that are being
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
674 // accumulator recursion variable eliminated.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
675 if (Ret->getNumOperands() == 1 && Ret->getReturnValue() != CI &&
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
676 !isa<UndefValue>(Ret->getReturnValue()) &&
|
|
77
|
677 AccumulatorRecursionEliminationInitVal == nullptr &&
|
|
|
678 !getCommonReturnValue(nullptr, CI)) {
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
679 // One case remains that we are able to handle: the current return
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
680 // instruction returns a constant, and all other return instructions
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
681 // return a different constant.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
682 if (!isDynamicConstant(Ret->getReturnValue(), CI, Ret))
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
683 return false; // Current return instruction does not return a constant.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
684 // Check that all other return instructions return a common constant. If
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
685 // so, record it in AccumulatorRecursionEliminationInitVal.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
686 AccumulatorRecursionEliminationInitVal = getCommonReturnValue(Ret, CI);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
687 if (!AccumulatorRecursionEliminationInitVal)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
688 return false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
689 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
690
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
691 BasicBlock *BB = Ret->getParent();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
692 Function *F = BB->getParent();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
693
|
|
77
|
694 emitOptimizationRemark(F->getContext(), "tailcallelim", *F, CI->getDebugLoc(),
|
|
|
695 "transforming tail recursion to loop");
|
|
|
696
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
697 // OK! We can transform this tail call. If this is the first one found,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
698 // create the new entry block, allowing us to branch back to the old entry.
|
|
77
|
699 if (!OldEntry) {
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
700 OldEntry = &F->getEntryBlock();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
701 BasicBlock *NewEntry = BasicBlock::Create(F->getContext(), "", F, OldEntry);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
702 NewEntry->takeName(OldEntry);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
703 OldEntry->setName("tailrecurse");
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
704 BranchInst::Create(OldEntry, NewEntry);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
705
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
706 // If this tail call is marked 'tail' and if there are any allocas in the
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
707 // entry block, move them up to the new entry block.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
708 TailCallsAreMarkedTail = CI->isTailCall();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
709 if (TailCallsAreMarkedTail)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
710 // Move all fixed sized allocas from OldEntry to NewEntry.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
711 for (BasicBlock::iterator OEBI = OldEntry->begin(), E = OldEntry->end(),
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
712 NEBI = NewEntry->begin(); OEBI != E; )
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
713 if (AllocaInst *AI = dyn_cast<AllocaInst>(OEBI++))
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
714 if (isa<ConstantInt>(AI->getArraySize()))
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
715 AI->moveBefore(NEBI);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
716
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
717 // Now that we have created a new block, which jumps to the entry
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
718 // block, insert a PHI node for each argument of the function.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
719 // For now, we initialize each PHI to only have the real arguments
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
720 // which are passed in.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
721 Instruction *InsertPos = OldEntry->begin();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
722 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
723 I != E; ++I) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
724 PHINode *PN = PHINode::Create(I->getType(), 2,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
725 I->getName() + ".tr", InsertPos);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
726 I->replaceAllUsesWith(PN); // Everyone use the PHI node now!
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
727 PN->addIncoming(I, NewEntry);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
728 ArgumentPHIs.push_back(PN);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
729 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
730 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
731
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
732 // If this function has self recursive calls in the tail position where some
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
733 // are marked tail and some are not, only transform one flavor or another. We
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
734 // have to choose whether we move allocas in the entry block to the new entry
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
735 // block or not, so we can't make a good choice for both. NOTE: We could do
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
736 // slightly better here in the case that the function has no entry block
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
737 // allocas.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
738 if (TailCallsAreMarkedTail && !CI->isTailCall())
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
739 return false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
740
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
741 // Ok, now that we know we have a pseudo-entry block WITH all of the
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
742 // required PHI nodes, add entries into the PHI node for the actual
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
743 // parameters passed into the tail-recursive call.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
744 for (unsigned i = 0, e = CI->getNumArgOperands(); i != e; ++i)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
745 ArgumentPHIs[i]->addIncoming(CI->getArgOperand(i), BB);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
746
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
747 // If we are introducing an accumulator variable to eliminate the recursion,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
748 // do so now. Note that we _know_ that no subsequent tail recursion
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
749 // eliminations will happen on this function because of the way the
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
750 // accumulator recursion predicate is set up.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
751 //
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
752 if (AccumulatorRecursionEliminationInitVal) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
753 Instruction *AccRecInstr = AccumulatorRecursionInstr;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
754 // Start by inserting a new PHI node for the accumulator.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
755 pred_iterator PB = pred_begin(OldEntry), PE = pred_end(OldEntry);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
756 PHINode *AccPN =
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
757 PHINode::Create(AccumulatorRecursionEliminationInitVal->getType(),
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
758 std::distance(PB, PE) + 1,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
759 "accumulator.tr", OldEntry->begin());
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
760
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
761 // Loop over all of the predecessors of the tail recursion block. For the
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
762 // real entry into the function we seed the PHI with the initial value,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
763 // computed earlier. For any other existing branches to this block (due to
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
764 // other tail recursions eliminated) the accumulator is not modified.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
765 // Because we haven't added the branch in the current block to OldEntry yet,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
766 // it will not show up as a predecessor.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
767 for (pred_iterator PI = PB; PI != PE; ++PI) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
768 BasicBlock *P = *PI;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
769 if (P == &F->getEntryBlock())
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
770 AccPN->addIncoming(AccumulatorRecursionEliminationInitVal, P);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
771 else
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
772 AccPN->addIncoming(AccPN, P);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
773 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
774
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
775 if (AccRecInstr) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
776 // Add an incoming argument for the current block, which is computed by
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
777 // our associative and commutative accumulator instruction.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
778 AccPN->addIncoming(AccRecInstr, BB);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
779
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
780 // Next, rewrite the accumulator recursion instruction so that it does not
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
781 // use the result of the call anymore, instead, use the PHI node we just
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
782 // inserted.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
783 AccRecInstr->setOperand(AccRecInstr->getOperand(0) != CI, AccPN);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
784 } else {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
785 // Add an incoming argument for the current block, which is just the
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
786 // constant returned by the current return instruction.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
787 AccPN->addIncoming(Ret->getReturnValue(), BB);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
788 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
789
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
790 // Finally, rewrite any return instructions in the program to return the PHI
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
791 // node instead of the "initval" that they do currently. This loop will
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
792 // actually rewrite the return value we are destroying, but that's ok.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
793 for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
794 if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator()))
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
795 RI->setOperand(0, AccPN);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
796 ++NumAccumAdded;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
797 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
798
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
799 // Now that all of the PHI nodes are in place, remove the call and
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
800 // ret instructions, replacing them with an unconditional branch.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
801 BranchInst *NewBI = BranchInst::Create(OldEntry, Ret);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
802 NewBI->setDebugLoc(CI->getDebugLoc());
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
803
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
804 BB->getInstList().erase(Ret); // Remove return.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
805 BB->getInstList().erase(CI); // Remove call.
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
806 ++NumEliminated;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
807 return true;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
808 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
809
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
810 bool TailCallElim::FoldReturnAndProcessPred(BasicBlock *BB,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
811 ReturnInst *Ret, BasicBlock *&OldEntry,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
812 bool &TailCallsAreMarkedTail,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
813 SmallVectorImpl<PHINode *> &ArgumentPHIs,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
814 bool CannotTailCallElimCallsMarkedTail) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
815 bool Change = false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
816
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
817 // If the return block contains nothing but the return and PHI's,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
818 // there might be an opportunity to duplicate the return in its
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
819 // predecessors and perform TRC there. Look for predecessors that end
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
820 // in unconditional branch and recursive call(s).
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
821 SmallVector<BranchInst*, 8> UncondBranchPreds;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
822 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
823 BasicBlock *Pred = *PI;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
824 TerminatorInst *PTI = Pred->getTerminator();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
825 if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
826 if (BI->isUnconditional())
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
827 UncondBranchPreds.push_back(BI);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
828 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
829
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
830 while (!UncondBranchPreds.empty()) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
831 BranchInst *BI = UncondBranchPreds.pop_back_val();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
832 BasicBlock *Pred = BI->getParent();
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
833 if (CallInst *CI = FindTRECandidate(BI, CannotTailCallElimCallsMarkedTail)){
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
834 DEBUG(dbgs() << "FOLDING: " << *BB
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
835 << "INTO UNCOND BRANCH PRED: " << *Pred);
|
|
83
|
836 ReturnInst *RI = FoldReturnIntoUncondBranch(Ret, BB, Pred);
|
|
|
837
|
|
|
838 // Cleanup: if all predecessors of BB have been eliminated by
|
|
|
839 // FoldReturnIntoUncondBranch, we would like to delete it, but we
|
|
|
840 // can not just nuke it as it is being used as an iterator by our caller.
|
|
|
841 // Just empty it, and the caller will erase it when it is safe to do so.
|
|
|
842 // It is important to empty it, because the ret instruction in there is
|
|
|
843 // still using a value which EliminateRecursiveTailCall will attempt
|
|
|
844 // to remove.
|
|
|
845 if (!BB->hasAddressTaken() && pred_begin(BB) == pred_end(BB))
|
|
|
846 BB->getInstList().clear();
|
|
|
847
|
|
|
848 EliminateRecursiveTailCall(CI, RI, OldEntry, TailCallsAreMarkedTail,
|
|
|
849 ArgumentPHIs,
|
0
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
850 CannotTailCallElimCallsMarkedTail);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
851 ++NumRetDuped;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
852 Change = true;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
853 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
854 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
855
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
856 return Change;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
857 }
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
858
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
859 bool
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
860 TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
861 bool &TailCallsAreMarkedTail,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
862 SmallVectorImpl<PHINode *> &ArgumentPHIs,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
863 bool CannotTailCallElimCallsMarkedTail) {
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
864 CallInst *CI = FindTRECandidate(Ret, CannotTailCallElimCallsMarkedTail);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
865 if (!CI)
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
866 return false;
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
867
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
868 return EliminateRecursiveTailCall(CI, Ret, OldEntry, TailCallsAreMarkedTail,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
869 ArgumentPHIs,
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
870 CannotTailCallElimCallsMarkedTail);
|
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff
changeset
|
871 }
|
