clang/lib/Lex/ScratchBuffer.cpp

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