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1 //===--- ScratchBuffer.cpp - Scratch space for forming tokens -------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8 //
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9 // This file implements the ScratchBuffer interface.
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10 //
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11 //===----------------------------------------------------------------------===//
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12
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13 #include "clang/Lex/ScratchBuffer.h"
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14 #include "clang/Basic/SourceManager.h"
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15 #include "llvm/Support/MemoryBuffer.h"
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16 #include <cstring>
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17 using namespace clang;
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18
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19 // ScratchBufSize - The size of each chunk of scratch memory. Slightly less
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20 //than a page, almost certainly enough for anything. :)
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21 static const unsigned ScratchBufSize = 4060;
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22
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23 ScratchBuffer::ScratchBuffer(SourceManager &SM)
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24 : SourceMgr(SM), CurBuffer(nullptr) {
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25 // Set BytesUsed so that the first call to getToken will require an alloc.
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26 BytesUsed = ScratchBufSize;
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27 }
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28
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29 /// getToken - Splat the specified text into a temporary MemoryBuffer and
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30 /// return a SourceLocation that refers to the token. This is just like the
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31 /// method below, but returns a location that indicates the physloc of the
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32 /// token.
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33 SourceLocation ScratchBuffer::getToken(const char *Buf, unsigned Len,
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34 const char *&DestPtr) {
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35 if (BytesUsed+Len+2 > ScratchBufSize)
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36 AllocScratchBuffer(Len+2);
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37 else {
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38 // Clear out the source line cache if it's already been computed.
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39 // FIXME: Allow this to be incrementally extended.
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40 auto *ContentCache = const_cast<SrcMgr::ContentCache *>(
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41 SourceMgr.getSLocEntry(SourceMgr.getFileID(BufferStartLoc))
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42 .getFile().getContentCache());
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43 ContentCache->SourceLineCache = nullptr;
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44 }
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45
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46 // Prefix the token with a \n, so that it looks like it is the first thing on
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47 // its own virtual line in caret diagnostics.
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48 CurBuffer[BytesUsed++] = '\n';
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49
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50 // Return a pointer to the character data.
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51 DestPtr = CurBuffer+BytesUsed;
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52
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53 // Copy the token data into the buffer.
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54 memcpy(CurBuffer+BytesUsed, Buf, Len);
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55
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56 // Remember that we used these bytes.
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57 BytesUsed += Len+1;
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58
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59 // Add a NUL terminator to the token. This keeps the tokens separated, in
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60 // case they get relexed, and puts them on their own virtual lines in case a
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61 // diagnostic points to one.
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62 CurBuffer[BytesUsed-1] = '\0';
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63
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64 return BufferStartLoc.getLocWithOffset(BytesUsed-Len-1);
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65 }
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66
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67 void ScratchBuffer::AllocScratchBuffer(unsigned RequestLen) {
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68 // Only pay attention to the requested length if it is larger than our default
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69 // page size. If it is, we allocate an entire chunk for it. This is to
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70 // support gigantic tokens, which almost certainly won't happen. :)
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71 if (RequestLen < ScratchBufSize)
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72 RequestLen = ScratchBufSize;
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73
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74 // Get scratch buffer. Zero-initialize it so it can be dumped into a PCH file
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75 // deterministically.
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76 std::unique_ptr<llvm::WritableMemoryBuffer> OwnBuf =
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77 llvm::WritableMemoryBuffer::getNewMemBuffer(RequestLen,
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78 "<scratch space>");
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79 CurBuffer = OwnBuf->getBufferStart();
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80 FileID FID = SourceMgr.createFileID(std::move(OwnBuf));
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81 BufferStartLoc = SourceMgr.getLocForStartOfFile(FID);
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82 BytesUsed = 0;
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83 }
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