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[clang][fat-lto-objects] Make module flags match non-FatLTO pipelines (…
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…#83159)

In addition to being rather hard to follow, there isn't a good reason
why FatLTO shouldn't just share the same code for setting module flags
for (Thin)LTO. This patch simplifies the logic and makes sure we use set
these flags in a consistent way, independent of FatLTO.

Additionally, we now test that output in the .llvm.lto section actually
matches the output from Full and Thin LTO compilation.
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@ilovepi
ilovepi committed Feb 29, 2024
1 parent daf3079 commit 7d8b50a
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Showing 2 changed files with 36 additions and 17 deletions.
32 changes: 16 additions & 16 deletions clang/lib/CodeGen/BackendUtil.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -186,6 +186,14 @@ class EmitAssemblyHelper {
TargetTriple.getVendor() != llvm::Triple::Apple;
}

/// Check whether we should emit a flag for UnifiedLTO.
/// The UnifiedLTO module flag should be set when UnifiedLTO is enabled for
/// ThinLTO or Full LTO with module summaries.
bool shouldEmitUnifiedLTOModueFlag() const {
return CodeGenOpts.UnifiedLTO &&
(CodeGenOpts.PrepareForThinLTO || shouldEmitRegularLTOSummary());
}

public:
EmitAssemblyHelper(DiagnosticsEngine &_Diags,
const HeaderSearchOptions &HeaderSearchOpts,
Expand Down Expand Up @@ -1036,7 +1044,8 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
if (!actionRequiresCodeGen(Action) && CodeGenOpts.VerifyModule)
MPM.addPass(VerifierPass());

if (Action == Backend_EmitBC || Action == Backend_EmitLL) {
if (Action == Backend_EmitBC || Action == Backend_EmitLL ||
CodeGenOpts.FatLTO) {
if (CodeGenOpts.PrepareForThinLTO && !CodeGenOpts.DisableLLVMPasses) {
if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
TheModule->addModuleFlag(llvm::Module::Error, "EnableSplitLTOUnit",
Expand All @@ -1047,11 +1056,9 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
if (!ThinLinkOS)
return;
}
if (CodeGenOpts.UnifiedLTO)
TheModule->addModuleFlag(llvm::Module::Error, "UnifiedLTO", uint32_t(1));
MPM.addPass(ThinLTOBitcodeWriterPass(
*OS, ThinLinkOS ? &ThinLinkOS->os() : nullptr));
} else {
} else if (Action == Backend_EmitLL) {
MPM.addPass(PrintModulePass(*OS, "", CodeGenOpts.EmitLLVMUseLists,
/*EmitLTOSummary=*/true));
}
Expand All @@ -1065,24 +1072,17 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
TheModule->addModuleFlag(llvm::Module::Error, "EnableSplitLTOUnit",
uint32_t(1));
if (CodeGenOpts.UnifiedLTO)
TheModule->addModuleFlag(llvm::Module::Error, "UnifiedLTO", uint32_t(1));
}
if (Action == Backend_EmitBC)
if (Action == Backend_EmitBC) {
MPM.addPass(BitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists,
EmitLTOSummary));
else
} else if (Action == Backend_EmitLL) {
MPM.addPass(PrintModulePass(*OS, "", CodeGenOpts.EmitLLVMUseLists,
EmitLTOSummary));
}
}
}
if (CodeGenOpts.FatLTO) {
// Set the EnableSplitLTOUnit and UnifiedLTO module flags, since FatLTO
// uses a different action than Backend_EmitBC or Backend_EmitLL.
if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
TheModule->addModuleFlag(llvm::Module::Error, "EnableSplitLTOUnit",
uint32_t(CodeGenOpts.EnableSplitLTOUnit));
if (CodeGenOpts.UnifiedLTO && !TheModule->getModuleFlag("UnifiedLTO"))

if (shouldEmitUnifiedLTOModueFlag())
TheModule->addModuleFlag(llvm::Module::Error, "UnifiedLTO", uint32_t(1));
}

Expand Down
21 changes: 20 additions & 1 deletion clang/test/CodeGen/fat-lto-objects.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -11,10 +11,11 @@
// RUN: llvm-objcopy --dump-section=.llvm.lto=%t.full.split.bc %t.full.split.o
// RUN: llvm-dis %t.full.split.bc -o - | FileCheck %s --check-prefixes=FULL,SPLIT,NOUNIFIED

/// Full LTO always sets EnableSplitLTOUnit when the summary is used.
// RUN: %clang -cc1 -triple x86_64-unknown-linux-gnu -flto=full -ffat-lto-objects -emit-obj < %s -o %t.full.nosplit.o
// RUN: llvm-readelf -S %t.full.nosplit.o | FileCheck %s --check-prefixes=ELF
// RUN: llvm-objcopy --dump-section=.llvm.lto=%t.full.nosplit.bc %t.full.nosplit.o
// RUN: llvm-dis %t.full.nosplit.bc -o - | FileCheck %s --check-prefixes=FULL,NOSPLIT,NOUNIFIED
// RUN: llvm-dis %t.full.nosplit.bc -o - | FileCheck %s --check-prefixes=FULL,SPLIT,NOUNIFIED

// RUN: %clang -cc1 -triple x86_64-unknown-linux-gnu -flto=thin -fsplit-lto-unit -ffat-lto-objects -emit-obj < %s -o %t.thin.split.o
// RUN: llvm-readelf -S %t.thin.split.o | FileCheck %s --check-prefixes=ELF
Expand All @@ -34,6 +35,21 @@
// RUN: %clang -cc1 -triple x86_64-unknown-linux-gnu -flto=full -ffat-lto-objects -fsplit-lto-unit -S < %s -o - \
// RUN: | FileCheck %s --check-prefixes=ASM

/// Make sure that FatLTO generates .llvm.lto sections that are the same as the output from normal LTO compilations
// RUN: %clang -O2 --target=x86_64-unknown-linux-gnu -fPIE -flto=full -ffat-lto-objects -c %s -o %t.fatlto.full.o
// RUN: llvm-objcopy --dump-section=.llvm.lto=%t.fatlto.full.bc %t.fatlto.full.o
// RUN: llvm-dis < %t.fatlto.full.bc -o %t.fatlto.full.ll
// RUN: %clang -O2 --target=x86_64-unknown-linux-gnu -fPIE -flto=full -c %s -o %t.nofat.full.bc
// RUN: llvm-dis < %t.nofat.full.bc -o %t.nofat.full.ll
// RUN: diff %t.fatlto.full.ll %t.nofat.full.ll

// RUN: %clang -O2 --target=x86_64-unknown-linux-gnu -fPIE -flto=thin -ffat-lto-objects -c %s -o %t.fatlto.thin.o
// RUN: llvm-objcopy --dump-section=.llvm.lto=%t.fatlto.thin.bc %t.fatlto.thin.o
// RUN: llvm-dis < %t.fatlto.thin.bc -o %t.fatlto.thin.ll
// RUN: %clang -O2 --target=x86_64-unknown-linux-gnu -fPIE -flto=thin -c %s -o %t.nofat.thin.bc
// RUN: llvm-dis < %t.nofat.thin.bc -o %t.nofat.thin.ll
// RUN: diff %t.fatlto.thin.ll %t.nofat.thin.ll

/// Be sure we enable split LTO units correctly under -ffat-lto-objects.
// SPLIT: ![[#]] = !{i32 1, !"EnableSplitLTOUnit", i32 1}
// NOSPLIT: ![[#]] = !{i32 1, !"EnableSplitLTOUnit", i32 0}
Expand All @@ -51,6 +67,9 @@
// ASM-NEXT: .asciz "BC
// ASM-NEXT: .size .Lllvm.embedded.object

const char* foo = "foo";

int test(void) {
const char* bar = "bar";
return 0xabcd;
}

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