clang  3.7.0
ScratchBuffer.cpp
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1 //===--- ScratchBuffer.cpp - Scratch space for forming tokens -------------===//
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 file implements the ScratchBuffer interface.
11 //
12 //===----------------------------------------------------------------------===//
13 
16 #include "llvm/Support/MemoryBuffer.h"
17 #include <cstring>
18 using namespace clang;
19 
20 // ScratchBufSize - The size of each chunk of scratch memory. Slightly less
21 //than a page, almost certainly enough for anything. :)
22 static const unsigned ScratchBufSize = 4060;
23 
25  : SourceMgr(SM), CurBuffer(nullptr) {
26  // Set BytesUsed so that the first call to getToken will require an alloc.
27  BytesUsed = ScratchBufSize;
28 }
29 
30 /// getToken - Splat the specified text into a temporary MemoryBuffer and
31 /// return a SourceLocation that refers to the token. This is just like the
32 /// method below, but returns a location that indicates the physloc of the
33 /// token.
34 SourceLocation ScratchBuffer::getToken(const char *Buf, unsigned Len,
35  const char *&DestPtr) {
36  if (BytesUsed+Len+2 > ScratchBufSize)
37  AllocScratchBuffer(Len+2);
38 
39  // Prefix the token with a \n, so that it looks like it is the first thing on
40  // its own virtual line in caret diagnostics.
41  CurBuffer[BytesUsed++] = '\n';
42 
43  // Return a pointer to the character data.
44  DestPtr = CurBuffer+BytesUsed;
45 
46  // Copy the token data into the buffer.
47  memcpy(CurBuffer+BytesUsed, Buf, Len);
48 
49  // Remember that we used these bytes.
50  BytesUsed += Len+1;
51 
52  // Add a NUL terminator to the token. This keeps the tokens separated, in
53  // case they get relexed, and puts them on their own virtual lines in case a
54  // diagnostic points to one.
55  CurBuffer[BytesUsed-1] = '\0';
56 
57  return BufferStartLoc.getLocWithOffset(BytesUsed-Len-1);
58 }
59 
60 void ScratchBuffer::AllocScratchBuffer(unsigned RequestLen) {
61  // Only pay attention to the requested length if it is larger than our default
62  // page size. If it is, we allocate an entire chunk for it. This is to
63  // support gigantic tokens, which almost certainly won't happen. :)
64  if (RequestLen < ScratchBufSize)
65  RequestLen = ScratchBufSize;
66 
67  // Get scratch buffer. Zero-initialize it so it can be dumped into a PCH file
68  // deterministically.
69  std::unique_ptr<llvm::MemoryBuffer> OwnBuf =
70  llvm::MemoryBuffer::getNewMemBuffer(RequestLen, "<scratch space>");
71  llvm::MemoryBuffer &Buf = *OwnBuf;
72  FileID FID = SourceMgr.createFileID(std::move(OwnBuf));
73  BufferStartLoc = SourceMgr.getLocForStartOfFile(FID);
74  CurBuffer = const_cast<char*>(Buf.getBufferStart());
75  BytesUsed = 0;
76 }
SourceLocation getToken(const char *Buf, unsigned Len, const char *&DestPtr)
Defines the SourceManager interface.
SourceLocation getLocWithOffset(int Offset) const
Return a source location with the specified offset from this SourceLocation.
static const unsigned ScratchBufSize
SourceManager & SM
FileID createFileID(const FileEntry *SourceFile, SourceLocation IncludePos, SrcMgr::CharacteristicKind FileCharacter, int LoadedID=0, unsigned LoadedOffset=0)
Create a new FileID that represents the specified file being #included from the specified IncludePosi...
SourceManager & SourceMgr
Definition: Format.cpp:1205
Encodes a location in the source. The SourceManager can decode this to get at the full include stack...
An opaque identifier used by SourceManager which refers to a source file (MemoryBuffer) along with it...
ScratchBuffer(SourceManager &SM)
SourceLocation getLocForStartOfFile(FileID FID) const
Return the source location corresponding to the first byte of the specified file. ...
This class handles loading and caching of source files into memory.