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>
17using namespace clang;
18
19// ScratchBufSize - The size of each chunk of scratch memory. Slightly less
20//than a page, almost certainly enough for anything. :)
21static const unsigned ScratchBufSize = 4060;
22
23ScratchBuffer::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.
33SourceLocation ScratchBuffer::getToken(const char *Buf, unsigned Len,
34 const char *&DestPtr) {
35 if (BytesUsed+Len+2 > ScratchBufSize)
36 AllocScratchBuffer(RequestLen: 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(FID: SourceMgr.getFileID(SpellingLoc: 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(dest: CurBuffer+BytesUsed, src: Buf, n: 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(Offset: BytesUsed-Len-1);
65}
66
67void 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(Size: RequestLen,
78 BufferName: "<scratch space>");
79 CurBuffer = OwnBuf->getBufferStart();
80 FileID FID = SourceMgr.createFileID(Buffer: std::move(OwnBuf));
81 BufferStartLoc = SourceMgr.getLocForStartOfFile(FID);
82 BytesUsed = 0;
83}
84

source code of clang/lib/Lex/ScratchBuffer.cpp