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[ThinLTO] Don't internalize weak writeable variables

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Variables with linkonce_odr and weak_odr linkage shouldn't be internalized
if they're not readonly. Otherwise we may end up with multiple copies of
such variable, so reads and writes will become inconsistent

Differential revision: https://reviews.llvm.org/D61255

llvm-svn: 360577
This commit is contained in:
Eugene Leviant 2019-05-13 11:53:05 +00:00
parent de2fa23e3a
commit 46dffcf69f
2 changed files with 55 additions and 1 deletions
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15
lib/LTO/LTO.cpp
View File

@ -371,6 +371,14 @@ void llvm::thinLTOResolvePrevailingInIndex(
GUIDPreservedSymbols);
}
static bool isWeakWriteableObject(GlobalValueSummary *GVS) {
if (auto *VarSummary = dyn_cast<GlobalVarSummary>(GVS->getBaseObject()))
return !VarSummary->isReadOnly() &&
(VarSummary->linkage() == GlobalValue::WeakODRLinkage ||
VarSummary->linkage() == GlobalValue::LinkOnceODRLinkage);
return false;
}
static void thinLTOInternalizeAndPromoteGUID(
GlobalValueSummaryList &GVSummaryList, GlobalValue::GUID GUID,
function_ref<bool(StringRef, GlobalValue::GUID)> isExported) {
@ -385,7 +393,12 @@ static void thinLTOInternalizeAndPromoteGUID(
S->linkage() != GlobalValue::AppendingLinkage &&
// We can't internalize available_externally globals because this
// can break function pointer equality.
S->linkage() != GlobalValue::AvailableExternallyLinkage)
S->linkage() != GlobalValue::AvailableExternallyLinkage &&
// Functions and read-only variables with linkonce_odr and weak_odr
// linkage can be internalized. We can't internalize linkonce_odr
// and weak_odr variables which are modified somewhere in the
// program because reads and writes will become inconsistent.
!isWeakWriteableObject(S.get()))
S->setLinkage(GlobalValue::InternalLinkage);
}
}

41
test/ThinLTO/X86/weak_externals.ll Normal file
View File

@ -0,0 +1,41 @@
; Test that linkonce_odr and weak_odr variables which are visible to regular
; object (and so are not readonly) are not internalized by thin LTO.
; RUN: opt -module-summary %s -o %t.bc
; RUN: llvm-lto2 run -save-temps %t.bc -o %t.out \
; RUN: -r=%t.bc,_ZL5initSv,plx \
; RUN: -r=%t.bc,_ZN9SingletonI1SE11getInstanceEv,lx \
; RUN: -r=%t.bc,_ZZN9SingletonI1SE11getInstanceEvE8instance,lx \
; RUN: -r=%t.bc,_ZZN9SingletonI1SE11getInstanceEvE13instance_weak,lx
; RUN: llvm-dis %t.out.1.1.promote.bc -o - | FileCheck %s
; CHECK: @_ZZN9SingletonI1SE11getInstanceEvE8instance = available_externally dso_local global %struct.S zeroinitializer
; CHECK: @_ZZN9SingletonI1SE11getInstanceEvE13instance_weak = available_externally dso_local global %struct.S* null, align 8
; CHECK: define internal dereferenceable(16) %struct.S* @_ZN9SingletonI1SE11getInstanceEv() comdat
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
%struct.S = type { i64, i64 }
$_ZN9SingletonI1SE11getInstanceEv = comdat any
$_ZZN9SingletonI1SE11getInstanceEvE8instance = comdat any
$_ZZN9SingletonI1SE11getInstanceEvE13instance_weak = comdat any
@_ZZN9SingletonI1SE11getInstanceEvE8instance = linkonce_odr dso_local global %struct.S zeroinitializer, comdat, align 8
@_ZZN9SingletonI1SE11getInstanceEvE13instance_weak = weak_odr dso_local global %struct.S* null, comdat, align 8
define dso_local void @_ZL5initSv() {
%1 = call dereferenceable(16) %struct.S* @_ZN9SingletonI1SE11getInstanceEv()
store %struct.S* %1, %struct.S** @_ZZN9SingletonI1SE11getInstanceEvE13instance_weak
%2 = getelementptr inbounds %struct.S, %struct.S* %1, i32 0, i32 0
store i64 1, i64* %2, align 8
ret void
}
define linkonce_odr dso_local dereferenceable(16) %struct.S* @_ZN9SingletonI1SE11getInstanceEv() #0 comdat align 2 {
ret %struct.S* @_ZZN9SingletonI1SE11getInstanceEvE8instance
}