nicolas/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Add an (optional) identification block in the bitcode

Browse Source 
Processing bitcode from a different LLVM version can lead to
unexpected behavior. The LLVM project guarantees autoupdating
bitcode from a previous minor revision for the same major, but
can't make any promise when reading bitcode generated from a
either a non-released LLVM, a vendor toolchain, or a "future"
LLVM release. This patch aims at being more user-friendly and
allows a bitcode produce to emit an optional block at the
beginning of the bitcode that will contains an opaque string
intended to describe the bitcode producer information. The
bitcode reader will dump this information alongside any error it
reports.

The optional block also includes an "epoch" number, monotonically
increasing when incompatible changes are made to the bitcode. The
reader will reject bitcode whose epoch is different from the one
expected.

Differential Revision: http://reviews.llvm.org/D13666

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 251325
This commit is contained in:
Mehdi Amini
2015-10-26 18:37:00 +00:00
parent d1aad26589
commit 5d303285b9
5 changed files with 142 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files

25
llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
View File

@@ -2829,6 +2829,29 @@ static void WriteCombinedFunctionSummary(const FunctionInfoIndex &I,
Stream.ExitBlock();
}
// Create the "IDENTIFICATION_BLOCK_ID" containing a single string with the
// current llvm version, and a record for the epoch number.
static void WriteIdentificationBlock(const Module *M, BitstreamWriter &Stream) {
Stream.EnterSubblock(bitc::IDENTIFICATION_BLOCK_ID, 5);
// Write the "user readable" string identifying the bitcode producer
BitCodeAbbrev *Abbv = new BitCodeAbbrev();
Abbv->Add(BitCodeAbbrevOp(bitc::IDENTIFICATION_CODE_STRING));
Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Char6));
auto StringAbbrev = Stream.EmitAbbrev(Abbv);
WriteStringRecord(bitc::IDENTIFICATION_CODE_STRING,
"LLVM" LLVM_VERSION_STRING, StringAbbrev, Stream);
// Write the epoch version
Abbv = new BitCodeAbbrev();
Abbv->Add(BitCodeAbbrevOp(bitc::IDENTIFICATION_CODE_EPOCH));
Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
SmallVector<unsigned, 1> Vals = {bitc::BITCODE_CURRENT_EPOCH};
Stream.EmitRecord(bitc::IDENTIFICATION_CODE_EPOCH, Vals);
Stream.ExitBlock();
}
/// WriteModule - Emit the specified module to the bitstream.
static void WriteModule(const Module *M, BitstreamWriter &Stream,
bool ShouldPreserveUseListOrder,
@@ -3000,6 +3023,8 @@ void llvm::WriteBitcodeToFile(const Module *M, raw_ostream &Out,
// Emit the file header.
WriteBitcodeHeader(Stream);
WriteIdentificationBlock(M, Stream);
// Emit the module.
WriteModule(M, Stream, ShouldPreserveUseListOrder, BitcodeStartBit,
EmitFunctionSummary);