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IR: Do not consider available_externally linkage to be linker-weak.

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From the linker's perspective, an available_externally global is equivalent
to an external declaration (per isDeclarationForLinker()), so it is incorrect
to consider it to be a weak definition.

Also clean up some logic in the dead argument elimination pass and clarify
its comments to better explain how its behavior depends on linkage,
introduce GlobalValue::isStrongDefinitionForLinker() and start using
it throughout the optimizers and backend.

Differential Revision: http://reviews.llvm.org/D10941

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241413 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Peter Collingbourne 2015-07-05 20:52:35 +00:00
parent 3b19ca3a2e
commit ce2b45bd7d
14 changed files with 55 additions and 71 deletions
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13
include/llvm/IR/GlobalValue.h
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@ -252,10 +252,9 @@ public:
/// mistake: when working at the IR level use mayBeOverridden instead as it
/// knows about ODR semantics.
static bool isWeakForLinker(LinkageTypes Linkage) {
return Linkage == AvailableExternallyLinkage || Linkage == WeakAnyLinkage ||
Linkage == WeakODRLinkage || Linkage == LinkOnceAnyLinkage ||
Linkage == LinkOnceODRLinkage || Linkage == CommonLinkage ||
Linkage == ExternalWeakLinkage;
return Linkage == WeakAnyLinkage || Linkage == WeakODRLinkage ||
Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage ||
Linkage == CommonLinkage || Linkage == ExternalWeakLinkage;
}
bool hasExternalLinkage() const { return isExternalLinkage(Linkage); }
@ -349,6 +348,12 @@ public:
return isDeclaration();
}
/// Returns true if this global's definition will be the one chosen by the
/// linker.
bool isStrongDefinitionForLinker() const {
return !(isDeclarationForLinker() || isWeakForLinker());
}
/// This method unlinks 'this' from the containing module, but does not delete
/// it.
virtual void removeFromParent() = 0;

2
lib/Analysis/ValueTracking.cpp
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@ -1464,7 +1464,7 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
// If the object is defined in the current Module, we'll be giving
// it the preferred alignment. Otherwise, we have to assume that it
// may only have the minimum ABI alignment.
if (!GVar->isDeclaration() && !GVar->isWeakForLinker())
if (GVar->isStrongDefinitionForLinker())
Align = DL.getPreferredAlignment(GVar);
else
Align = DL.getABITypeAlignment(ObjectType);

4
lib/CodeGen/SelectionDAG/TargetLowering.cpp
View File

@ -265,9 +265,7 @@ TargetLowering::isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const {
// In dynamic-no-pic mode, assume that known defined values are safe.
if (getTargetMachine().getRelocationModel() == Reloc::DynamicNoPIC &&
GA &&
!GA->getGlobal()->isDeclaration() &&
!GA->getGlobal()->isWeakForLinker())
GA && GA->getGlobal()->isStrongDefinitionForLinker())
return true;
// Otherwise assume nothing is safe.

8
lib/Target/AArch64/AArch64Subtarget.cpp
View File

@ -57,7 +57,7 @@ AArch64Subtarget::AArch64Subtarget(const Triple &TT, const std::string &CPU,
unsigned char
AArch64Subtarget::ClassifyGlobalReference(const GlobalValue *GV,
const TargetMachine &TM) const {
bool isDecl = GV->isDeclarationForLinker();
bool isDef = GV->isStrongDefinitionForLinker();
// MachO large model always goes via a GOT, simply to get a single 8-byte
// absolute relocation on all global addresses.
@ -66,8 +66,7 @@ AArch64Subtarget::ClassifyGlobalReference(const GlobalValue *GV,
// The small code mode's direct accesses use ADRP, which cannot necessarily
// produce the value 0 (if the code is above 4GB).
if (TM.getCodeModel() == CodeModel::Small &&
GV->isWeakForLinker() && isDecl) {
if (TM.getCodeModel() == CodeModel::Small && GV->hasExternalWeakLinkage()) {
// In PIC mode use the GOT, but in absolute mode use a constant pool load.
if (TM.getRelocationModel() == Reloc::Static)
return AArch64II::MO_CONSTPOOL;
@ -85,8 +84,7 @@ AArch64Subtarget::ClassifyGlobalReference(const GlobalValue *GV,
// defined could end up in unexpected places. Use a GOT.
if (TM.getRelocationModel() != Reloc::Static && GV->hasDefaultVisibility()) {
if (isTargetMachO())
return (isDecl || GV->isWeakForLinker()) ? AArch64II::MO_GOT
: AArch64II::MO_NO_FLAG;
return isDef ? AArch64II::MO_NO_FLAG : AArch64II::MO_GOT;
else
// No need to go through the GOT for local symbols on ELF.
return GV->hasLocalLinkage() ? AArch64II::MO_NO_FLAG : AArch64II::MO_GOT;

6
lib/Target/ARM/ARMISelLowering.cpp
View File

@ -1734,12 +1734,12 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
} else if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
const GlobalValue *GV = G->getGlobal();
isDirect = true;
bool isExt = GV->isDeclaration() || GV->isWeakForLinker();
bool isStub = (isExt && Subtarget->isTargetMachO()) &&
bool isDef = GV->isStrongDefinitionForLinker();
bool isStub = (!isDef && Subtarget->isTargetMachO()) &&
getTargetMachine().getRelocationModel() != Reloc::Static;
isARMFunc = !Subtarget->isThumb() || (isStub && !Subtarget->isMClass());
// ARM call to a local ARM function is predicable.
isLocalARMFunc = !Subtarget->isThumb() && (!isExt || !ARMInterworking);
isLocalARMFunc = !Subtarget->isThumb() && (isDef || !ARMInterworking);
// tBX takes a register source operand.
if (isStub && Subtarget->isThumb1Only() && !Subtarget->hasV5TOps()) {
assert(Subtarget->isTargetMachO() && "WrapperPIC use on non-MachO?");

36
lib/Target/ARM/ARMSubtarget.cpp
View File

@ -286,7 +286,7 @@ ARMSubtarget::GVIsIndirectSymbol(const GlobalValue *GV,
if (RelocM == Reloc::Static)
return false;
bool isDecl = GV->isDeclarationForLinker();
bool isDef = GV->isStrongDefinitionForLinker();
if (!isTargetMachO()) {
// Extra load is needed for all externally visible.
@ -294,34 +294,22 @@ ARMSubtarget::GVIsIndirectSymbol(const GlobalValue *GV,
return false;
return true;
} else {
// If this is a strong reference to a definition, it is definitely not
// through a stub.
if (isDef)
return false;
// Unless we have a symbol with hidden visibility, we have to go through a
// normal $non_lazy_ptr stub because this symbol might be resolved late.
if (!GV->hasHiddenVisibility()) // Non-hidden $non_lazy_ptr reference.
return true;
if (RelocM == Reloc::PIC_) {
// If this is a strong reference to a definition, it is definitely not
// through a stub.
if (!isDecl && !GV->isWeakForLinker())
return false;
// Unless we have a symbol with hidden visibility, we have to go through a
// normal $non_lazy_ptr stub because this symbol might be resolved late.
if (!GV->hasHiddenVisibility()) // Non-hidden $non_lazy_ptr reference.
return true;
// If symbol visibility is hidden, we have a stub for common symbol
// references and external declarations.
if (isDecl || GV->hasCommonLinkage())
if (GV->isDeclarationForLinker() || GV->hasCommonLinkage())
// Hidden $non_lazy_ptr reference.
return true;
return false;
} else {
// If this is a strong reference to a definition, it is definitely not
// through a stub.
if (!isDecl && !GV->isWeakForLinker())
return false;
// Unless we have a symbol with hidden visibility, we have to go through a
// normal $non_lazy_ptr stub because this symbol might be resolved late.
if (!GV->hasHiddenVisibility()) // Non-hidden $non_lazy_ptr reference.
return true;
}
}

6
lib/Target/PowerPC/PPCAsmPrinter.cpp
View File

@ -197,7 +197,7 @@ void PPCAsmPrinter::printOperand(const MachineInstr *MI, unsigned OpNo,
// External or weakly linked global variables need non-lazily-resolved stubs
if (TM.getRelocationModel() != Reloc::Static &&
(GV->isDeclaration() || GV->isWeakForLinker())) {
!GV->isStrongDefinitionForLinker()) {
if (!GV->hasHiddenVisibility()) {
SymToPrint = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr");
MachineModuleInfoImpl::StubValueTy &StubSym =
@ -624,7 +624,7 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
IsExternal = GV->isDeclaration();
IsCommon = GV->hasCommonLinkage();
IsNonLocalFunction = GV->getType()->getElementType()->isFunctionTy() &&
(GV->isDeclaration() || GV->isWeakForLinker());
!GV->isStrongDefinitionForLinker();
IsAvailExt = GV->hasAvailableExternallyLinkage();
} else if (MO.isCPI())
MOSymbol = GetCPISymbol(MO.getIndex());
@ -706,7 +706,7 @@ void PPCAsmPrinter::EmitInstruction(const MachineInstr *MI) {
MOSymbol = getSymbol(GV);
IsExternal = GV->isDeclaration();
IsNonLocalFunction = GV->getType()->getElementType()->isFunctionTy() &&
(GV->isDeclaration() || GV->isWeakForLinker());
!GV->isStrongDefinitionForLinker();
} else if (MO.isCPI())
MOSymbol = GetCPISymbol(MO.getIndex());

2
lib/Target/PowerPC/PPCFastISel.cpp
View File

@ -1979,7 +1979,7 @@ unsigned PPCFastISel::PPCMaterializeGV(const GlobalValue *GV, MVT VT) {
// on the "if" path here.
if (CModel == CodeModel::Large ||
(GV->getType()->getElementType()->isFunctionTy() &&
(GV->isDeclaration() || GV->isWeakForLinker())) ||
!GV->isStrongDefinitionForLinker()) ||
GV->isDeclaration() || GV->hasCommonLinkage() ||
GV->hasAvailableExternallyLinkage())
BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(PPC::LDtocL),

2
lib/Target/PowerPC/PPCISelDAGToDAG.cpp
View File

@ -2901,7 +2901,7 @@ SDNode *PPCDAGToDAGISel::Select(SDNode *N) {
if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(GA)) {
const GlobalValue *GValue = G->getGlobal();
if ((GValue->getType()->getElementType()->isFunctionTy() &&
(GValue->isDeclaration() || GValue->isWeakForLinker())) ||
!GValue->isStrongDefinitionForLinker()) ||
GValue->isDeclaration() || GValue->hasCommonLinkage() ||
GValue->hasAvailableExternallyLinkage())
return transferMemOperands(N, CurDAG->getMachineNode(PPC::LDtocL, dl,

6
lib/Target/PowerPC/PPCISelLowering.cpp
View File

@ -4084,8 +4084,7 @@ unsigned PrepareCall(SelectionDAG &DAG, SDValue &Callee, SDValue &InFlag,
if ((DAG.getTarget().getRelocationModel() != Reloc::Static &&
(Subtarget.getTargetTriple().isMacOSX() &&
Subtarget.getTargetTriple().isMacOSXVersionLT(10, 5)) &&
(G->getGlobal()->isDeclaration() ||
G->getGlobal()->isWeakForLinker())) ||
!G->getGlobal()->isStrongDefinitionForLinker()) ||
(Subtarget.isTargetELF() && !isPPC64 &&
!G->getGlobal()->hasLocalLinkage() &&
DAG.getTarget().getRelocationModel() == Reloc::PIC_)) {
@ -4254,8 +4253,7 @@ static
bool isLocalCall(const SDValue &Callee)
{
if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee))
return !G->getGlobal()->isDeclaration() &&
!G->getGlobal()->isWeakForLinker();
return G->getGlobal()->isStrongDefinitionForLinker();
return false;
}

2
lib/Target/X86/X86FastISel.cpp
View File

@ -3108,7 +3108,7 @@ bool X86FastISel::fastLowerCall(CallLoweringInfo &CLI) {
GV->hasDefaultVisibility() && !GV->hasLocalLinkage()) {
OpFlags = X86II::MO_PLT;
} else if (Subtarget->isPICStyleStubAny() &&
(GV->isDeclaration() || GV->isWeakForLinker()) &&
!GV->isStrongDefinitionForLinker() &&
(!Subtarget->getTargetTriple().isMacOSX() ||
Subtarget->getTargetTriple().isMacOSXVersionLT(10, 5))) {
// PC-relative references to external symbols should go through $stub,

2
lib/Target/X86/X86ISelLowering.cpp
View File

@ -3109,7 +3109,7 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
GV->hasDefaultVisibility() && !GV->hasLocalLinkage()) {
OpFlags = X86II::MO_PLT;
} else if (Subtarget->isPICStyleStubAny() &&
(GV->isDeclaration() || GV->isWeakForLinker()) &&
!GV->isStrongDefinitionForLinker() &&
(!Subtarget->getTargetTriple().isMacOSX() ||
Subtarget->getTargetTriple().isMacOSXVersionLT(10, 5))) {
// PC-relative references to external symbols should go through $stub,

11
lib/Target/X86/X86Subtarget.cpp
View File

@ -68,7 +68,7 @@ ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
if (GV->hasDLLImportStorageClass())
return X86II::MO_DLLIMPORT;
bool isDecl = GV->isDeclarationForLinker();
bool isDef = GV->isStrongDefinitionForLinker();
// X86-64 in PIC mode.
if (isPICStyleRIPRel()) {
@ -80,8 +80,7 @@ ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
// If symbol visibility is hidden, the extra load is not needed if
// target is x86-64 or the symbol is definitely defined in the current
// translation unit.
if (GV->hasDefaultVisibility() &&
(isDecl || GV->isWeakForLinker()))
if (GV->hasDefaultVisibility() && !isDef)
return X86II::MO_GOTPCREL;
} else if (!isTargetWin64()) {
assert(isTargetELF() && "Unknown rip-relative target");
@ -107,7 +106,7 @@ ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
// If this is a strong reference to a definition, it is definitely not
// through a stub.
if (!isDecl && !GV->isWeakForLinker())
if (isDef)
return X86II::MO_PIC_BASE_OFFSET;
// Unless we have a symbol with hidden visibility, we have to go through a
@ -117,7 +116,7 @@ ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
// If symbol visibility is hidden, we have a stub for common symbol
// references and external declarations.
if (isDecl || GV->hasCommonLinkage()) {
if (GV->isDeclarationForLinker() || GV->hasCommonLinkage()) {
// Hidden $non_lazy_ptr reference.
return X86II::MO_DARWIN_HIDDEN_NONLAZY_PIC_BASE;
}
@ -131,7 +130,7 @@ ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
// If this is a strong reference to a definition, it is definitely not
// through a stub.
if (!isDecl && !GV->isWeakForLinker())
if (isDef)
return X86II::MO_NO_FLAG;
// Unless we have a symbol with hidden visibility, we have to go through a

26
lib/Transforms/IPO/DeadArgumentElimination.cpp
View File

@ -326,7 +326,18 @@ bool DAE::DeleteDeadVarargs(Function &Fn) {
/// instead.
bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
{
if (Fn.isDeclaration() || Fn.mayBeOverridden())
// We cannot change the arguments if this TU does not define the function or
// if the linker may choose a function body from another TU, even if the
// nominal linkage indicates that other copies of the function have the same
// semantics. In the below example, the dead load from %p may not have been
// eliminated from the linker-chosen copy of f, so replacing %p with undef
// in callers may introduce undefined behavior.
//
// define linkonce_odr void @f(i32* %p) {
// %v = load i32 %p
// ret void
// }
if (!Fn.isStrongDefinitionForLinker())
return false;
// Functions with local linkage should already have been handled, except the
@ -334,19 +345,6 @@ bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
return false;
// If a function seen at compile time is not necessarily the one linked to
// the binary being built, it is illegal to change the actual arguments
// passed to it. These functions can be captured by isWeakForLinker().
// *NOTE* that mayBeOverridden() is insufficient for this purpose as it
// doesn't include linkage types like AvailableExternallyLinkage and
// LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of
// *EQUIVALENT* globals that can be merged at link-time. However, the
// semantic of *EQUIVALENT*-functions includes parameters. Changing
// parameters breaks this assumption.
//
if (Fn.isWeakForLinker())
return false;
if (Fn.use_empty())
return false;