[llvm] r268607 - LTOCodeGenerator: add linkonce(_odr) to "llvm.compiler.used" when present in "MustPreserve" set
Mehdi Amini via llvm-commits
llvm-commits at lists.llvm.org
Wed May 4 22:14:24 PDT 2016
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.
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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