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 
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.
34 SourceLocation ScratchBuffer::getToken(const char *Buf, unsigned Len,
35                                        const char *&DestPtr) {
36   if (BytesUsed+Len+2 > ScratchBufSize)
37     AllocScratchBuffer(Len+2);
38   else {
39     // Clear out the source line cache if it's already been computed.
40     // FIXME: Allow this to be incrementally extended.
41     auto *ContentCache = const_cast<SrcMgr::ContentCache *>(
42         SourceMgr.getSLocEntry(SourceMgr.getFileID(BufferStartLoc))
43                  .getFile().getContentCache());
44     ContentCache->SourceLineCache = nullptr;
45   }
46 
47   // Prefix the token with a \n, so that it looks like it is the first thing on
48   // its own virtual line in caret diagnostics.
49   CurBuffer[BytesUsed++] = '\n';
50 
51   // Return a pointer to the character data.
52   DestPtr = CurBuffer+BytesUsed;
53 
54   // Copy the token data into the buffer.
55   memcpy(CurBuffer+BytesUsed, Buf, Len);
56 
57   // Remember that we used these bytes.
58   BytesUsed += Len+1;
59 
60   // Add a NUL terminator to the token.  This keeps the tokens separated, in
61   // case they get relexed, and puts them on their own virtual lines in case a
62   // diagnostic points to one.
63   CurBuffer[BytesUsed-1] = '\0';
64 
65   return BufferStartLoc.getLocWithOffset(BytesUsed-Len-1);
66 }
67 
68 void ScratchBuffer::AllocScratchBuffer(unsigned RequestLen) {
69   // Only pay attention to the requested length if it is larger than our default
70   // page size.  If it is, we allocate an entire chunk for it.  This is to
71   // support gigantic tokens, which almost certainly won't happen. :)
72   if (RequestLen < ScratchBufSize)
73     RequestLen = ScratchBufSize;
74 
75   // Get scratch buffer. Zero-initialize it so it can be dumped into a PCH file
76   // deterministically.
77   std::unique_ptr<llvm::WritableMemoryBuffer> OwnBuf =
78       llvm::WritableMemoryBuffer::getNewMemBuffer(RequestLen,
79                                                   "<scratch space>");
80   CurBuffer = OwnBuf->getBufferStart();
81   FileID FID = SourceMgr.createFileID(std::move(OwnBuf));
82   BufferStartLoc = SourceMgr.getLocForStartOfFile(FID);
83   BytesUsed = 0;
84 }
85