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(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    auto *ContentCache = const_cast<SrcMgr::ContentCache *>(
41        SourceMgr.getSLocEntry(SourceMgr.getFileID(BufferStartLoc))
42                 .getFile().getContentCache());
43    ContentCache->SourceLineCache = nullptr;
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
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(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