xref: /freebsd/contrib/llvm-project/clang/lib/Lex/ScratchBuffer.cpp (revision 7fdf597e96a02165cfe22ff357b857d5fa15ed8a)
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 }
84