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LTO: Link non-prevailing weak_odr or linkonce_odr globals into the combined module with available_externally linkage.

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These linkages mean that the ultimately prevailing symbol will have the same
semantics as any non-prevailing copy of the symbol, so we are free to ignore
the linker's resolution.

Differential Revision: https://reviews.llvm.org/D29367

llvm-svn: 293865
This commit is contained in:
Peter Collingbourne 2017-02-02 05:22:42 +00:00
parent 4ab9ae596a
commit 615d8261c2
3 changed files with 36 additions and 4 deletions
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21
lib/LTO/LTO.cpp
View File

@ -446,6 +446,11 @@ Error LTO::addRegularLTO(BitcodeModule BM, const SymbolResolution *&ResI,
if (GV.hasAppendingLinkage())
Keep.push_back(&GV);
DenseSet<GlobalObject *> AliasedGlobals;
for (auto &GA : M.aliases())
if (GlobalObject *GO = GA.getBaseObject())
AliasedGlobals.insert(GO);
for (const InputFile::Symbol &Sym :
make_range(InputFile::symbol_iterator(SymTab.symbols().begin(), SymTab,
nullptr),
@ -471,13 +476,21 @@ Error LTO::addRegularLTO(BitcodeModule BM, const SymbolResolution *&ResI,
GV->setLinkage(GlobalValue::WeakODRLinkage);
break;
}
} else if (GV->hasAvailableExternallyLinkage()) {
// We can link available_externally symbols even if they are
// non-prevailing.
} else if (isa<GlobalObject>(GV) &&
(GV->hasLinkOnceODRLinkage() || GV->hasWeakODRLinkage() ||
GV->hasAvailableExternallyLinkage()) &&
!AliasedGlobals.count(cast<GlobalObject>(GV))) {
// Either of the above three types of linkage indicates that the
// chosen prevailing symbol will have the same semantics as this copy of
// the symbol, so we can link it with available_externally linkage. We
// only need to do this if the symbol is undefined.
GlobalValue *CombinedGV =
RegularLTO.CombinedModule->getNamedValue(GV->getName());
if (!CombinedGV || CombinedGV->isDeclaration())
if (!CombinedGV || CombinedGV->isDeclaration()) {
Keep.push_back(GV);
GV->setLinkage(GlobalValue::AvailableExternallyLinkage);
cast<GlobalObject>(GV)->setComdat(nullptr);
}
}
}
// Common resolution: collect the maximum size/alignment over all commons.

6
test/LTO/Resolution/X86/Inputs/link-odr-availextern-odr.ll Normal file
View File

@ -0,0 +1,6 @@
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
define linkonce_odr i32 @f() {
ret i32 2
}

13
test/LTO/Resolution/X86/link-odr-availextern.ll
View File

@ -3,16 +3,29 @@
; RUN: llvm-as %s -o %t1
; RUN: llvm-as %S/Inputs/link-odr-availextern-ae.ll -o %t2ae
; RUN: llvm-as %S/Inputs/link-odr-availextern-odr.ll -o %t2odr
; RUN: llvm-lto2 -o %t3 %t1 %t2ae -r %t1,f,p -r %t2ae,f, -save-temps
; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=PREVAILING %s
; RUN: llvm-lto2 -o %t3 %t1 %t2odr -r %t1,f,p -r %t2odr,f, -save-temps
; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=PREVAILING %s
; RUN: llvm-lto2 -o %t3 %t2ae %t1 -r %t1,f,p -r %t2ae,f, -save-temps
; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=PREVAILING %s
; RUN: llvm-lto2 -o %t3 %t2odr %t1 -r %t1,f,p -r %t2odr,f, -save-temps
; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=PREVAILING %s
; RUN: llvm-lto2 -o %t3 %t2ae -r %t2ae,f, -save-temps
; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=NONPREVAILING %s
; RUN: llvm-lto2 -o %t3 %t2odr -r %t2odr,f, -save-temps
; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=NONPREVAILING %s
; RUN: llvm-lto2 -o %t3 %t2odr %t1 -r %t1,f, -r %t2odr,f, -save-temps
; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=NONPREVAILING %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"