<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Wed, May 4, 2016 at 10:14 PM, Mehdi Amini via llvm-commits <span dir="ltr"><<a href="mailto:llvm-commits@lists.llvm.org" target="_blank">llvm-commits@lists.llvm.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: mehdi_amini<br>
Date: Thu May 5 00:14:24 2016<br>
New Revision: 268607<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=268607&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=268607&view=rev</a><br>
Log:<br>
LTOCodeGenerator: add linkonce(_odr) to "llvm.compiler.used" when present in "MustPreserve" set<br>
<br>
If the linker requested to preserve a linkonce function, we should<br>
honor this even if we drop all uses.<br>
We explicitely avoid turning them into weak_odr (unlike the first<br>
version of this patch in r267644), because the codegen can be<br>
different on Darwin: because of `llvm::canBeOmittedFromSymbolTable()`<br>
we may emit the symbol as weak_def_can_be_hidden instead of<br>
weak_definition.<br></blockquote><div><br></div><div>Do we only do this on Darwin then, and otherwise turn it into weak_odr everywhere else?</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
From: Mehdi Amini <<a href="mailto:mehdi.amini@apple.com">mehdi.amini@apple.com</a>><br>
<br>
Modified:<br>
llvm/trunk/lib/LTO/LTOCodeGenerator.cpp<br>
llvm/trunk/test/tools/lto/hide-linkonce-odr.ll<br>
<br>
Modified: llvm/trunk/lib/LTO/LTOCodeGenerator.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/LTO/LTOCodeGenerator.cpp?rev=268607&r1=268606&r2=268607&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/LTO/LTOCodeGenerator.cpp?rev=268607&r1=268606&r2=268607&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/lib/LTO/LTOCodeGenerator.cpp (original)<br>
+++ llvm/trunk/lib/LTO/LTOCodeGenerator.cpp Thu May 5 00:14:24 2016<br>
@@ -348,8 +348,73 @@ std::unique_ptr<TargetMachine> LTOCodeGe<br>
RelocModel, CodeModel::Default, CGOptLevel));<br>
}<br>
<br>
+// If a linkonce global is present in the MustPreserveSymbols, we need to make<br>
+// sure we honor this. To force the compiler to not drop it, we add it to the<br>
+// "llvm.compiler.used" global.<br>
+static void preserveDiscardableGVs(<br>
+ Module &TheModule,<br>
+ llvm::function_ref<bool(const GlobalValue &)> mustPreserveGV) {<br>
+ SetVector<Constant *> UsedValuesSet;<br>
+ if (GlobalVariable *LLVMUsed =<br>
+ TheModule.getGlobalVariable("llvm.compiler.used")) {<br>
+ ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());<br>
+ for (auto &V : Inits->operands())<br>
+ UsedValuesSet.insert(cast<Constant>(&V));<br>
+ LLVMUsed->eraseFromParent();<br>
+ }<br>
+ llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(TheModule.getContext());<br>
+ auto mayPreserveGlobal = [&](GlobalValue &GV) {<br>
+ if (!GV.isDiscardableIfUnused() || GV.isDeclaration())<br>
+ return;<br>
+ if (!mustPreserveGV(GV))<br>
+ return;<br>
+ assert(!GV.hasAvailableExternallyLinkage() && !GV.hasInternalLinkage());<br>
+ UsedValuesSet.insert(ConstantExpr::getBitCast(&GV, i8PTy));<br>
+ };<br>
+ for (auto &GV : TheModule)<br>
+ mayPreserveGlobal(GV);<br>
+ for (auto &GV : TheModule.globals())<br>
+ mayPreserveGlobal(GV);<br>
+ for (auto &GV : TheModule.aliases())<br>
+ mayPreserveGlobal(GV);<br>
+<br>
+ if (UsedValuesSet.empty())<br>
+ return;<br>
+<br>
+ llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, UsedValuesSet.size());<br>
+ auto *LLVMUsed = new llvm::GlobalVariable(<br>
+ TheModule, ATy, false, llvm::GlobalValue::AppendingLinkage,<br>
+ llvm::ConstantArray::get(ATy, UsedValuesSet.getArrayRef()),<br>
+ "llvm.compiler.used");<br>
+ LLVMUsed->setSection("llvm.metadata");<br>
+}<br>
+<br>
void LTOCodeGenerator::applyScopeRestrictions() {<br>
- if (ScopeRestrictionsDone || !ShouldInternalize)<br>
+ if (ScopeRestrictionsDone)<br>
+ return;<br>
+<br>
+ // Declare a callback for the internalize pass that will ask for every<br>
+ // candidate GlobalValue if it can be internalized or not.<br>
+ SmallString<64> MangledName;<br>
+ auto mustPreserveGV = [&](const GlobalValue &GV) -> bool {<br>
+ // Unnamed globals can't be mangled, but they can't be preserved either.<br>
+ if (!GV.hasName())<br>
+ return false;<br>
+<br>
+ // Need to mangle the GV as the "MustPreserveSymbols" StringSet is filled<br>
+ // with the linker supplied name, which on Darwin includes a leading<br>
+ // underscore.<br>
+ MangledName.clear();<br>
+ MangledName.reserve(GV.getName().size() + 1);<br>
+ Mangler::getNameWithPrefix(MangledName, GV.getName(),<br>
+ MergedModule->getDataLayout());<br>
+ return MustPreserveSymbols.count(MangledName);<br>
+ };<br>
+<br>
+ // Preserve linkonce value on linker request<br>
+ preserveDiscardableGVs(*MergedModule, mustPreserveGV);<br>
+<br>
+ if (!ShouldInternalize)<br>
return;<br>
<br>
if (ShouldRestoreGlobalsLinkage) {<br>
@@ -373,22 +438,7 @@ void LTOCodeGenerator::applyScopeRestric<br>
// symbols referenced from asm<br>
UpdateCompilerUsed(*MergedModule, *TargetMach, AsmUndefinedRefs);<br>
<br>
- // Declare a callback for the internalize pass that will ask for every<br>
- // candidate GlobalValue if it can be internalized or not.<br>
- Mangler Mangler;<br>
- SmallString<64> MangledName;<br>
- auto MustPreserveGV = [&](const GlobalValue &GV) -> bool {<br>
- // Need to mangle the GV as the "MustPreserveSymbols" StringSet is filled<br>
- // with the linker supplied name, which on Darwin includes a leading<br>
- // underscore.<br>
- MangledName.clear();<br>
- MangledName.reserve(GV.getName().size() + 1);<br>
- Mangler::getNameWithPrefix(MangledName, GV.getName(),<br>
- MergedModule->getDataLayout());<br>
- return MustPreserveSymbols.count(MangledName);<br>
- };<br>
-<br>
- internalizeModule(*MergedModule, MustPreserveGV);<br>
+ internalizeModule(*MergedModule, mustPreserveGV);<br>
<br>
ScopeRestrictionsDone = true;<br>
}<br>
<br>
Modified: llvm/trunk/test/tools/lto/hide-linkonce-odr.ll<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/lto/hide-linkonce-odr.ll?rev=268607&r1=268606&r2=268607&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/lto/hide-linkonce-odr.ll?rev=268607&r1=268606&r2=268607&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/test/tools/lto/hide-linkonce-odr.ll (original)<br>
+++ llvm/trunk/test/tools/lto/hide-linkonce-odr.ll Thu May 5 00:14:24 2016<br>
@@ -1,21 +1,28 @@<br>
; RUN: llvm-as %s -o %t.o<br>
-; 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<br>
+; 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<br>
<br>
; RUN: llvm-dis %t.dylib.lto.opt.bc -o - | FileCheck --check-prefix=IR %s<br>
-; check that @a is still a linkonce_odr definition<br>
-; IR: define linkonce_odr void @a()<br>
+; check that @a is no longer a linkonce_odr definition<br>
+; IR-NOT: define linkonce_odr void @a()<br>
+; check that @b is appended in llvm.used<br>
+; 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"<br>
<br>
; RUN: llvm-nm %t.dylib | FileCheck --check-prefix=NM %s<br>
-; check that the linker can hide @a but not @b<br>
+; check that the linker can hide @a but not @b, nor @GlobLinkonce<br>
+; NM: 0000000000000f48 S _GlobLinkonce<br>
; NM: 0000000000000f10 t _a<br>
; NM: 0000000000000f20 T _b<br>
; NM: 0000000000000f00 T _c<br>
<br>
+<br>
target triple = "x86_64-apple-macosx10.10.0"<br>
<br>
declare void @external()<br>
<br>
+@GlobLinkonce = linkonce_odr unnamed_addr constant [1 x i8*] [i8* null], align 8<br>
+<br>
define linkonce_odr void @a() noinline {<br>
+ %use_of_GlobLinkonce = load [1 x i8*], [1 x i8*] *@GlobLinkonce<br>
call void @external()<br>
ret void<br>
}<br>
<br>
<br>
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</blockquote></div><br></div></div>