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Set alignment of .llvmbc and .llvmcmd to 1

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Otherwise their alignment is dependent on the size of the section.  If the size
is large than 16, the alignment will be 16.

16 is a bad choice for both .llvmbc and .llvmcmd because the padding between two
contributions from input sections is of a variable size.

A bitstream is actually guaranteed to be 4-byte aligned, but consumers don't
need this property.
This commit is contained in:
Fangrui Song
2020-08-29 18:27:34 -07:00
parent 4fbf0636a2
commit 6ae7b403c3
4 changed files with 12 additions and 8 deletions
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4
llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
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@@ -4852,6 +4852,9 @@ void llvm::EmbedBitcodeInModule(llvm::Module &M, llvm::MemoryBufferRef Buf,
M, ModuleConstant->getType(), true, llvm::GlobalValue::PrivateLinkage,
ModuleConstant);
GV->setSection(getSectionNameForBitcode(T));
// Set alignment to 1 to prevent padding between two contributions from input
// sections after linking.
GV->setAlignment(Align(1));
UsedArray.push_back(
ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
if (llvm::GlobalVariable *Old =
@@ -4875,6 +4878,7 @@ void llvm::EmbedBitcodeInModule(llvm::Module &M, llvm::MemoryBufferRef Buf,
llvm::GlobalValue::PrivateLinkage,
CmdConstant);
GV->setSection(getSectionNameForCommandline(T));
GV->setAlignment(Align(1));
UsedArray.push_back(
ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
if (llvm::GlobalVariable *Old = M.getGlobalVariable("llvm.cmdline", true)) {