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comparison lib/CodeGen/SpillPlacement.h @ 0:95c75e76d11b LLVM3.4

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LLVM 3.4
author Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date Thu, 12 Dec 2013 13:56:28 +0900
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children 54457678186b
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-1:000000000000 0:95c75e76d11b
1 //===-- SpillPlacement.h - Optimal Spill Code Placement --------*- C++ -*--===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This analysis computes the optimal spill code placement between basic blocks.
11 //
12 // The runOnMachineFunction() method only precomputes some profiling information
13 // about the CFG. The real work is done by prepare(), addConstraints(), and
14 // finish() which are called by the register allocator.
15 //
16 // Given a variable that is live across multiple basic blocks, and given
17 // constraints on the basic blocks where the variable is live, determine which
18 // edge bundles should have the variable in a register and which edge bundles
19 // should have the variable in a stack slot.
20 //
21 // The returned bit vector can be used to place optimal spill code at basic
22 // block entries and exits. Spill code placement inside a basic block is not
23 // considered.
24 //
25 //===----------------------------------------------------------------------===//
26
27 #ifndef LLVM_CODEGEN_SPILLPLACEMENT_H
28 #define LLVM_CODEGEN_SPILLPLACEMENT_H
29
30 #include "llvm/ADT/ArrayRef.h"
31 #include "llvm/ADT/SmallVector.h"
32 #include "llvm/CodeGen/MachineFunctionPass.h"
33 #include "llvm/Support/BlockFrequency.h"
34
35 namespace llvm {
36
37 class BitVector;
38 class EdgeBundles;
39 class MachineBasicBlock;
40 class MachineLoopInfo;
41
42 class SpillPlacement : public MachineFunctionPass {
43 struct Node;
44 const MachineFunction *MF;
45 const EdgeBundles *bundles;
46 const MachineLoopInfo *loops;
47 Node *nodes;
48
49 // Nodes that are active in the current computation. Owned by the prepare()
50 // caller.
51 BitVector *ActiveNodes;
52
53 // Nodes with active links. Populated by scanActiveBundles.
54 SmallVector<unsigned, 8> Linked;
55
56 // Nodes that went positive during the last call to scanActiveBundles or
57 // iterate.
58 SmallVector<unsigned, 8> RecentPositive;
59
60 // Block frequencies are computed once. Indexed by block number.
61 SmallVector<BlockFrequency, 4> BlockFrequencies;
62
63 public:
64 static char ID; // Pass identification, replacement for typeid.
65
66 SpillPlacement() : MachineFunctionPass(ID), nodes(0) {}
67 ~SpillPlacement() { releaseMemory(); }
68
69 /// BorderConstraint - A basic block has separate constraints for entry and
70 /// exit.
71 enum BorderConstraint {
72 DontCare, ///< Block doesn't care / variable not live.
73 PrefReg, ///< Block entry/exit prefers a register.
74 PrefSpill, ///< Block entry/exit prefers a stack slot.
75 PrefBoth, ///< Block entry prefers both register and stack.
76 MustSpill ///< A register is impossible, variable must be spilled.
77 };
78
79 /// BlockConstraint - Entry and exit constraints for a basic block.
80 struct BlockConstraint {
81 unsigned Number; ///< Basic block number (from MBB::getNumber()).
82 BorderConstraint Entry : 8; ///< Constraint on block entry.
83 BorderConstraint Exit : 8; ///< Constraint on block exit.
84
85 /// True when this block changes the value of the live range. This means
86 /// the block has a non-PHI def. When this is false, a live-in value on
87 /// the stack can be live-out on the stack without inserting a spill.
88 bool ChangesValue;
89 };
90
91 /// prepare - Reset state and prepare for a new spill placement computation.
92 /// @param RegBundles Bit vector to receive the edge bundles where the
93 /// variable should be kept in a register. Each bit
94 /// corresponds to an edge bundle, a set bit means the
95 /// variable should be kept in a register through the
96 /// bundle. A clear bit means the variable should be
97 /// spilled. This vector is retained.
98 void prepare(BitVector &RegBundles);
99
100 /// addConstraints - Add constraints and biases. This method may be called
101 /// more than once to accumulate constraints.
102 /// @param LiveBlocks Constraints for blocks that have the variable live in or
103 /// live out.
104 void addConstraints(ArrayRef<BlockConstraint> LiveBlocks);
105
106 /// addPrefSpill - Add PrefSpill constraints to all blocks listed. This is
107 /// equivalent to calling addConstraint with identical BlockConstraints with
108 /// Entry = Exit = PrefSpill, and ChangesValue = false.
109 ///
110 /// @param Blocks Array of block numbers that prefer to spill in and out.
111 /// @param Strong When true, double the negative bias for these blocks.
112 void addPrefSpill(ArrayRef<unsigned> Blocks, bool Strong);
113
114 /// addLinks - Add transparent blocks with the given numbers.
115 void addLinks(ArrayRef<unsigned> Links);
116
117 /// scanActiveBundles - Perform an initial scan of all bundles activated by
118 /// addConstraints and addLinks, updating their state. Add all the bundles
119 /// that now prefer a register to RecentPositive.
120 /// Prepare internal data structures for iterate.
121 /// Return true is there are any positive nodes.
122 bool scanActiveBundles();
123
124 /// iterate - Update the network iteratively until convergence, or new bundles
125 /// are found.
126 void iterate();
127
128 /// getRecentPositive - Return an array of bundles that became positive during
129 /// the previous call to scanActiveBundles or iterate.
130 ArrayRef<unsigned> getRecentPositive() { return RecentPositive; }
131
132 /// finish - Compute the optimal spill code placement given the
133 /// constraints. No MustSpill constraints will be violated, and the smallest
134 /// possible number of PrefX constraints will be violated, weighted by
135 /// expected execution frequencies.
136 /// The selected bundles are returned in the bitvector passed to prepare().
137 /// @return True if a perfect solution was found, allowing the variable to be
138 /// in a register through all relevant bundles.
139 bool finish();
140
141 /// getBlockFrequency - Return the estimated block execution frequency per
142 /// function invocation.
143 BlockFrequency getBlockFrequency(unsigned Number) const {
144 return BlockFrequencies[Number];
145 }
146
147 private:
148 virtual bool runOnMachineFunction(MachineFunction&);
149 virtual void getAnalysisUsage(AnalysisUsage&) const;
150 virtual void releaseMemory();
151
152 void activate(unsigned);
153 };
154
155 } // end namespace llvm
156
157 #endif