[llvm] r268607 - LTOCodeGenerator: add linkonce(_odr) to "llvm.compiler.used" when present in "MustPreserve" set
David Blaikie via llvm-commits
llvm-commits at lists.llvm.org
Thu May 5 11:25:31 PDT 2016
On Wed, May 4, 2016 at 10:14 PM, Mehdi Amini via llvm-commits <
llvm-commits at lists.llvm.org> wrote:
> Author: mehdi_amini
> Date: Thu May 5 00:14:24 2016
> New Revision: 268607
>
> URL: http://llvm.org/viewvc/llvm-project?rev=268607&view=rev
> Log:
> LTOCodeGenerator: add linkonce(_odr) to "llvm.compiler.used" when present
> in "MustPreserve" set
>
> If the linker requested to preserve a linkonce function, we should
> honor this even if we drop all uses.
> We explicitely avoid turning them into weak_odr (unlike the first
> version of this patch in r267644), because the codegen can be
> different on Darwin: because of `llvm::canBeOmittedFromSymbolTable()`
> we may emit the symbol as weak_def_can_be_hidden instead of
> weak_definition.
>
Do we only do this on Darwin then, and otherwise turn it into weak_odr
everywhere else?
>
> From: Mehdi Amini <mehdi.amini at apple.com>
>
> Modified:
> llvm/trunk/lib/LTO/LTOCodeGenerator.cpp
> llvm/trunk/test/tools/lto/hide-linkonce-odr.ll
>
> Modified: llvm/trunk/lib/LTO/LTOCodeGenerator.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/LTO/LTOCodeGenerator.cpp?rev=268607&r1=268606&r2=268607&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/LTO/LTOCodeGenerator.cpp (original)
> +++ llvm/trunk/lib/LTO/LTOCodeGenerator.cpp Thu May 5 00:14:24 2016
> @@ -348,8 +348,73 @@ std::unique_ptr<TargetMachine> LTOCodeGe
> RelocModel, CodeModel::Default,
> CGOptLevel));
> }
>
> +// If a linkonce global is present in the MustPreserveSymbols, we need to
> make
> +// sure we honor this. To force the compiler to not drop it, we add it to
> the
> +// "llvm.compiler.used" global.
> +static void preserveDiscardableGVs(
> + Module &TheModule,
> + llvm::function_ref<bool(const GlobalValue &)> mustPreserveGV) {
> + SetVector<Constant *> UsedValuesSet;
> + if (GlobalVariable *LLVMUsed =
> + TheModule.getGlobalVariable("llvm.compiler.used")) {
> + ConstantArray *Inits =
> cast<ConstantArray>(LLVMUsed->getInitializer());
> + for (auto &V : Inits->operands())
> + UsedValuesSet.insert(cast<Constant>(&V));
> + LLVMUsed->eraseFromParent();
> + }
> + llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(TheModule.getContext());
> + auto mayPreserveGlobal = [&](GlobalValue &GV) {
> + if (!GV.isDiscardableIfUnused() || GV.isDeclaration())
> + return;
> + if (!mustPreserveGV(GV))
> + return;
> + assert(!GV.hasAvailableExternallyLinkage() &&
> !GV.hasInternalLinkage());
> + UsedValuesSet.insert(ConstantExpr::getBitCast(&GV, i8PTy));
> + };
> + for (auto &GV : TheModule)
> + mayPreserveGlobal(GV);
> + for (auto &GV : TheModule.globals())
> + mayPreserveGlobal(GV);
> + for (auto &GV : TheModule.aliases())
> + mayPreserveGlobal(GV);
> +
> + if (UsedValuesSet.empty())
> + return;
> +
> + llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy,
> UsedValuesSet.size());
> + auto *LLVMUsed = new llvm::GlobalVariable(
> + TheModule, ATy, false, llvm::GlobalValue::AppendingLinkage,
> + llvm::ConstantArray::get(ATy, UsedValuesSet.getArrayRef()),
> + "llvm.compiler.used");
> + LLVMUsed->setSection("llvm.metadata");
> +}
> +
> void LTOCodeGenerator::applyScopeRestrictions() {
> - if (ScopeRestrictionsDone || !ShouldInternalize)
> + if (ScopeRestrictionsDone)
> + return;
> +
> + // Declare a callback for the internalize pass that will ask for every
> + // candidate GlobalValue if it can be internalized or not.
> + SmallString<64> MangledName;
> + auto mustPreserveGV = [&](const GlobalValue &GV) -> bool {
> + // Unnamed globals can't be mangled, but they can't be preserved
> either.
> + if (!GV.hasName())
> + return false;
> +
> + // Need to mangle the GV as the "MustPreserveSymbols" StringSet is
> filled
> + // with the linker supplied name, which on Darwin includes a leading
> + // underscore.
> + MangledName.clear();
> + MangledName.reserve(GV.getName().size() + 1);
> + Mangler::getNameWithPrefix(MangledName, GV.getName(),
> + MergedModule->getDataLayout());
> + return MustPreserveSymbols.count(MangledName);
> + };
> +
> + // Preserve linkonce value on linker request
> + preserveDiscardableGVs(*MergedModule, mustPreserveGV);
> +
> + if (!ShouldInternalize)
> return;
>
> if (ShouldRestoreGlobalsLinkage) {
> @@ -373,22 +438,7 @@ void LTOCodeGenerator::applyScopeRestric
> // symbols referenced from asm
> UpdateCompilerUsed(*MergedModule, *TargetMach, AsmUndefinedRefs);
>
> - // Declare a callback for the internalize pass that will ask for every
> - // candidate GlobalValue if it can be internalized or not.
> - Mangler Mangler;
> - SmallString<64> MangledName;
> - auto MustPreserveGV = [&](const GlobalValue &GV) -> bool {
> - // Need to mangle the GV as the "MustPreserveSymbols" StringSet is
> filled
> - // with the linker supplied name, which on Darwin includes a leading
> - // underscore.
> - MangledName.clear();
> - MangledName.reserve(GV.getName().size() + 1);
> - Mangler::getNameWithPrefix(MangledName, GV.getName(),
> - MergedModule->getDataLayout());
> - return MustPreserveSymbols.count(MangledName);
> - };
> -
> - internalizeModule(*MergedModule, MustPreserveGV);
> + internalizeModule(*MergedModule, mustPreserveGV);
>
> ScopeRestrictionsDone = true;
> }
>
> Modified: llvm/trunk/test/tools/lto/hide-linkonce-odr.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/lto/hide-linkonce-odr.ll?rev=268607&r1=268606&r2=268607&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/tools/lto/hide-linkonce-odr.ll (original)
> +++ llvm/trunk/test/tools/lto/hide-linkonce-odr.ll Thu May 5 00:14:24 2016
> @@ -1,21 +1,28 @@
> ; RUN: llvm-as %s -o %t.o
> -; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -dylib -arch x86_64
> -macosx_version_min 10.10.0 -lSystem -o %t.dylib %t.o -save-temps
> -undefined dynamic_lookup
> +; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -dylib -arch x86_64
> -macosx_version_min 10.10.0 -lSystem -o %t.dylib %t.o -save-temps
> -undefined dynamic_lookup -exported_symbol _c -exported_symbol _b
> -exported_symbol _GlobLinkonce
>
> ; RUN: llvm-dis %t.dylib.lto.opt.bc -o - | FileCheck --check-prefix=IR %s
> -; check that @a is still a linkonce_odr definition
> -; IR: define linkonce_odr void @a()
> +; check that @a is no longer a linkonce_odr definition
> +; IR-NOT: define linkonce_odr void @a()
> +; check that @b is appended in llvm.used
> +; IR: @llvm.compiler.used = appending global [2 x i8*] [i8* bitcast ([1 x
> i8*]* @GlobLinkonce to i8*), i8* bitcast (void ()* @b to i8*)], section
> "llvm.metadata"
>
> ; RUN: llvm-nm %t.dylib | FileCheck --check-prefix=NM %s
> -; check that the linker can hide @a but not @b
> +; check that the linker can hide @a but not @b, nor @GlobLinkonce
> +; NM: 0000000000000f48 S _GlobLinkonce
> ; NM: 0000000000000f10 t _a
> ; NM: 0000000000000f20 T _b
> ; NM: 0000000000000f00 T _c
>
> +
> target triple = "x86_64-apple-macosx10.10.0"
>
> declare void @external()
>
> + at GlobLinkonce = linkonce_odr unnamed_addr constant [1 x i8*] [i8* null],
> align 8
> +
> define linkonce_odr void @a() noinline {
> + %use_of_GlobLinkonce = load [1 x i8*], [1 x i8*] *@GlobLinkonce
> call void @external()
> ret void
> }
>
>
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