[llvm] r275474 - [ThinLTO/gold] Perform index-based weak/linkonce resolution
Teresa Johnson via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 14 14:13:24 PDT 2016
Author: tejohnson
Date: Thu Jul 14 16:13:24 2016
New Revision: 275474
URL: http://llvm.org/viewvc/llvm-project?rev=275474&view=rev
Log:
[ThinLTO/gold] Perform index-based weak/linkonce resolution
Summary:
Invoke the weak/linkonce symbol resolution support (already used by
libLTO) that operates via the summary index.
This ensures prevailing linkonce are kept, by making them weak, and
marks preempted copies as available_externally when possible.
With this change, the older support for keeping the prevailing linkonce
(by changing their symbol resolution) is removed.
Reviewers: mehdi_amini
Subscribers: llvm-commits, mehdi_amini
Differential Revision: http://reviews.llvm.org/D22302
Added:
llvm/trunk/test/tools/gold/X86/Inputs/thinlto_weak_resolution.ll
llvm/trunk/test/tools/gold/X86/thinlto_weak_resolution.ll
Modified:
llvm/trunk/tools/gold/gold-plugin.cpp
Added: llvm/trunk/test/tools/gold/X86/Inputs/thinlto_weak_resolution.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/gold/X86/Inputs/thinlto_weak_resolution.ll?rev=275474&view=auto
==============================================================================
--- llvm/trunk/test/tools/gold/X86/Inputs/thinlto_weak_resolution.ll (added)
+++ llvm/trunk/test/tools/gold/X86/Inputs/thinlto_weak_resolution.ll Thu Jul 14 16:13:24 2016
@@ -0,0 +1,37 @@
+target triple = "x86_64-unknown-linux-gnu"
+
+; Alias are not optimized
+ at linkonceodralias = linkonce_odr alias void (), void ()* @linkonceodrfuncwithalias
+
+; Alias are not optimized
+ at linkoncealias = linkonce alias void (), void ()* @linkoncefuncwithalias
+
+; Function with an alias are not optimized
+define linkonce_odr void @linkonceodrfuncwithalias() #0 {
+entry:
+ ret void
+}
+
+; Function with an alias are not optimized
+define linkonce void @linkoncefuncwithalias() #0 {
+entry:
+ ret void
+}
+
+define linkonce_odr void @linkonceodrfunc() #0 {
+entry:
+ ret void
+}
+define linkonce void @linkoncefunc() #0 {
+entry:
+ ret void
+}
+define weak_odr void @weakodrfunc() #0 {
+entry:
+ ret void
+}
+define weak void @weakfunc() #0 {
+entry:
+ ret void
+}
+
Added: llvm/trunk/test/tools/gold/X86/thinlto_weak_resolution.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/gold/X86/thinlto_weak_resolution.ll?rev=275474&view=auto
==============================================================================
--- llvm/trunk/test/tools/gold/X86/thinlto_weak_resolution.ll (added)
+++ llvm/trunk/test/tools/gold/X86/thinlto_weak_resolution.ll Thu Jul 14 16:13:24 2016
@@ -0,0 +1,87 @@
+; RUN: opt -module-summary %s -o %t.o
+; RUN: opt -module-summary %p/Inputs/thinlto_weak_resolution.ll -o %t2.o
+
+; Verify that prevailing weak for linker symbol is kept.
+; Note that gold picks the first copy of a function as the prevailing one,
+; so listing %t.o first is sufficient to ensure that its copies are prevailing.
+; RUN: %gold -m elf_x86_64 -plugin %llvmshlibdir/LLVMgold.so \
+; RUN: --plugin-opt=thinlto \
+; RUN: --plugin-opt=save-temps \
+; RUN: -shared \
+; RUN: -o %t3.o %t.o %t2.o
+
+; RUN: llvm-nm %t3.o | FileCheck %s
+; CHECK: weakfunc
+
+; All of the preempted functions should have been eliminated (the plugin will
+; not link them in).
+; RUN: llvm-dis %t2.o.opt.bc -o - | FileCheck --check-prefix=OPT2 %s
+; OPT2-NOT: @
+
+; RUN: llvm-dis %t.o.opt.bc -o - | FileCheck --check-prefix=OPT %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+
+define i32 @main() #0 {
+entry:
+ call void @linkonceodralias()
+ call void @linkoncealias()
+ call void @linkonceodrfuncwithalias()
+ call void @linkoncefuncwithalias()
+ call void @linkonceodrfunc()
+ call void @linkoncefunc()
+ call void @weakodrfunc()
+ call void @weakfunc()
+ call void @linkonceodrfuncInSingleModule()
+ ret i32 0
+}
+
+; Alias are resolved
+; OPT: @linkonceodralias = weak_odr alias void (), void ()* @linkonceodrfuncwithalias
+ at linkonceodralias = linkonce_odr alias void (), void ()* @linkonceodrfuncwithalias
+
+; Alias are resolved
+; OPT: @linkoncealias = weak alias void (), void ()* @linkoncefuncwithalias
+ at linkoncealias = linkonce alias void (), void ()* @linkoncefuncwithalias
+
+; Function with an alias are not optimized
+; OPT: define linkonce_odr void @linkonceodrfuncwithalias()
+define linkonce_odr void @linkonceodrfuncwithalias() #0 {
+entry:
+ ret void
+}
+
+; Function with an alias are not optimized
+; OPT: define linkonce void @linkoncefuncwithalias()
+define linkonce void @linkoncefuncwithalias() #0 {
+entry:
+ ret void
+}
+
+; OPT: define weak_odr void @linkonceodrfunc()
+define linkonce_odr void @linkonceodrfunc() #0 {
+entry:
+ ret void
+}
+; OPT: define weak void @linkoncefunc()
+define linkonce void @linkoncefunc() #0 {
+entry:
+ ret void
+}
+; OPT: define weak_odr void @weakodrfunc()
+define weak_odr void @weakodrfunc() #0 {
+entry:
+ ret void
+}
+; OPT: define weak void @weakfunc()
+define weak void @weakfunc() #0 {
+entry:
+ ret void
+}
+
+; OPT: weak_odr void @linkonceodrfuncInSingleModule()
+define linkonce_odr void @linkonceodrfuncInSingleModule() #0 {
+entry:
+ ret void
+}
Modified: llvm/trunk/tools/gold/gold-plugin.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/gold/gold-plugin.cpp?rev=275474&r1=275473&r2=275474&view=diff
==============================================================================
--- llvm/trunk/tools/gold/gold-plugin.cpp (original)
+++ llvm/trunk/tools/gold/gold-plugin.cpp Thu Jul 14 16:13:24 2016
@@ -735,16 +735,6 @@ getModuleForFile(LLVMContext &Context, c
if (Resolution == LDPR_PREVAILING_DEF_IRONLY_EXP && !Res.IsLinkonceOdr)
Resolution = LDPR_PREVAILING_DEF;
- // In ThinLTO mode change all prevailing resolutions to LDPR_PREVAILING_DEF.
- // For ThinLTO the IR files are compiled through the backend independently,
- // so we need to ensure that any prevailing linkonce copy will be emitted
- // into the object file by making it weak. Additionally, we can skip the
- // IRONLY handling for internalization, which isn't performed in ThinLTO
- // mode currently anyway.
- if (options::thinlto && (Resolution == LDPR_PREVAILING_DEF_IRONLY_EXP ||
- Resolution == LDPR_PREVAILING_DEF_IRONLY))
- Resolution = LDPR_PREVAILING_DEF;
-
GV->setUnnamedAddr(Res.UnnamedAddr);
GV->setVisibility(Res.Visibility);
@@ -998,6 +988,9 @@ void CodeGen::runLTOPasses() {
M->setDataLayout(TM->createDataLayout());
if (CombinedIndex) {
+ // Apply summary-based LinkOnce/Weak resolution decisions.
+ thinLTOResolveWeakForLinkerModule(*M, *DefinedGlobals);
+
// Apply summary-based internalization decisions. Skip if there are no
// defined globals from the summary since not only is it unnecessary, but
// if this module did not have a summary section the internalizer will
@@ -1322,6 +1315,10 @@ static ld_plugin_status thinLTOLink(raw_
// are referenced outside of a single IR module.
DenseSet<GlobalValue::GUID> Preserve;
+ // Keep track of the prevailing copy for each GUID, for use in resolving
+ // weak linkages.
+ DenseMap<GlobalValue::GUID, const GlobalValueSummary *> PrevailingCopy;
+
ModuleSummaryIndex CombinedIndex;
uint64_t NextModuleId = 0;
for (claimed_file &F : Modules) {
@@ -1342,19 +1339,27 @@ static ld_plugin_status thinLTOLink(raw_
std::unique_ptr<ModuleSummaryIndex> Index = getModuleSummaryIndexForFile(F);
- // Skip files without a module summary.
- if (Index)
- CombinedIndex.mergeFrom(std::move(Index), ++NextModuleId);
-
// Use gold's symbol resolution information to identify symbols referenced
- // by more than a single IR module (before importing, which is checked
- // separately).
+ // by more than a single IR module (i.e. referenced by multiple IR modules
+ // or by a non-IR module). Cross references introduced by importing are
+ // checked separately via the export lists. Also track the prevailing copy
+ // for later symbol resolution.
for (auto &Sym : F.syms) {
ld_plugin_symbol_resolution Resolution =
(ld_plugin_symbol_resolution)Sym.resolution;
+ GlobalValue::GUID SymGUID = GlobalValue::getGUID(Sym.name);
if (Resolution != LDPR_PREVAILING_DEF_IRONLY)
- Preserve.insert(GlobalValue::getGUID(Sym.name));
+ Preserve.insert(SymGUID);
+
+ if (Index && (Resolution == LDPR_PREVAILING_DEF ||
+ Resolution == LDPR_PREVAILING_DEF_IRONLY ||
+ Resolution == LDPR_PREVAILING_DEF_IRONLY_EXP))
+ PrevailingCopy[SymGUID] = Index->getGlobalValueSummary(SymGUID);
}
+
+ // Skip files without a module summary.
+ if (Index)
+ CombinedIndex.mergeFrom(std::move(Index), ++NextModuleId);
}
// Collect for each module the list of function it defines (GUID ->
@@ -1368,6 +1373,12 @@ static ld_plugin_status thinLTOLink(raw_
ComputeCrossModuleImport(CombinedIndex, ModuleToDefinedGVSummaries,
ImportLists, ExportLists);
+ auto isPrevailing = [&](GlobalValue::GUID GUID, const GlobalValueSummary *S) {
+ const auto &Prevailing = PrevailingCopy.find(GUID);
+ assert(Prevailing != PrevailingCopy.end());
+ return Prevailing->second == S;
+ };
+
// Callback for internalization, to prevent internalization of symbols
// that were not candidates initially, and those that are being imported
// (which introduces new cross references).
@@ -1378,6 +1389,11 @@ static ld_plugin_status thinLTOLink(raw_
Preserve.count(GUID);
};
+ thinLTOResolveWeakForLinkerInIndex(
+ CombinedIndex, isPrevailing,
+ [](StringRef ModuleIdentifier, GlobalValue::GUID GUID,
+ GlobalValue::LinkageTypes NewLinkage) {});
+
// Use global summary-based analysis to identify symbols that can be
// internalized (because they aren't exported or preserved as per callback).
// Changes are made in the index, consumed in the ThinLTO backends.
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