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
14 #include "clang/Lex/ScratchBuffer.h"
15 #include "clang/Basic/SourceManager.h"
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
ScratchBuffer(SourceManager & SM)24 ScratchBuffer::ScratchBuffer(SourceManager &SM)
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.
getToken(const char * Buf,unsigned Len,const char * & DestPtr)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
AllocScratchBuffer(unsigned RequestLen)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 }
77