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Don't load values out of global constants with weak

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linkage: the value may be replaced with something
different at link time.  (Frontends that want to
allow values to be loaded out of weak constants can
give their constants weak_odr linkage).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@67407 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2009-03-20 21:53:29 +00:00
parent db95fa131a
commit ab6b226978
5 changed files with 58 additions and 6 deletions
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7
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -11215,14 +11215,15 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
// Instcombine load (constant global) into the value loaded.
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Op))
if (GV->isConstant() && !GV->isDeclaration())
if (GV->isConstant() && !GV->isDeclaration() && !GV->mayBeOverridden())
return ReplaceInstUsesWith(LI, GV->getInitializer());
// Instcombine load (constantexpr_GEP global, 0, ...) into the value loaded.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op)) {
if (CE->getOpcode() == Instruction::GetElementPtr) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
if (GV->isConstant() && !GV->isDeclaration())
if (GV->isConstant() && !GV->isDeclaration() &&
!GV->mayBeOverridden())
if (Constant *V =
ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE))
return ReplaceInstUsesWith(LI, V);
@ -11246,7 +11247,7 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
// If this load comes from anywhere in a constant global, and if the global
// is all undef or zero, we know what it loads.
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Op->getUnderlyingObject())){
if (GV->isConstant() && GV->hasInitializer()) {
if (GV->isConstant() && GV->hasInitializer() && !GV->mayBeOverridden()) {
if (GV->getInitializer()->isNullValue())
return ReplaceInstUsesWith(LI, Constant::getNullValue(LI.getType()));
else if (isa<UndefValue>(GV->getInitializer()))

4
lib/Transforms/Scalar/SCCP.cpp
View File

@ -1131,7 +1131,7 @@ void SCCPSolver::visitLoadInst(LoadInst &I) {
// Transform load (constant global) into the value loaded.
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
if (GV->isConstant()) {
if (!GV->isDeclaration()) {
if (!GV->isDeclaration() && !GV->mayBeOverridden()) {
markConstant(IV, &I, GV->getInitializer());
return;
}
@ -1150,7 +1150,7 @@ void SCCPSolver::visitLoadInst(LoadInst &I) {
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
if (CE->getOpcode() == Instruction::GetElementPtr)
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
if (GV->isConstant() && !GV->isDeclaration())
if (GV->isConstant() && !GV->isDeclaration() && !GV->mayBeOverridden())
if (Constant *V =
ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
markConstant(IV, &I, V);

3
lib/Transforms/Utils/CloneFunction.cpp
View File

@ -335,7 +335,8 @@ ConstantFoldMappedInstruction(const Instruction *I) {
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[0]))
if (!LI->isVolatile() && CE->getOpcode() == Instruction::GetElementPtr)
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
if (GV->isConstant() && !GV->isDeclaration())
if (GV->isConstant() && !GV->isDeclaration() &&
!GV->mayBeOverridden())
return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(),
CE);

38
test/Feature/weak_constant.ll Normal file
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@ -0,0 +1,38 @@
; RUN: llvm-as < %s | opt -std-compile-opts | llvm-dis > %t
; RUN: grep undef %t | count 1
; RUN: grep 5 %t | count 1
; RUN: grep 7 %t | count 1
; RUN: grep 9 %t | count 1
type { i32, i32 } ; type %0
@a = weak constant i32 undef ; <i32*> [#uses=1]
@b = weak constant i32 5 ; <i32*> [#uses=1]
@c = weak constant %0 { i32 7, i32 9 } ; <%0*> [#uses=1]
define i32 @la() {
%v = load i32* @a ; <i32> [#uses=1]
ret i32 %v
}
define i32 @lb() {
%v = load i32* @b ; <i32> [#uses=1]
ret i32 %v
}
define i32 @lc() {
%g = getelementptr %0* @c, i32 0, i32 0 ; <i32*> [#uses=1]
%u = load i32* %g ; <i32> [#uses=1]
%h = getelementptr %0* @c, i32 0, i32 1 ; <i32*> [#uses=1]
%v = load i32* %h ; <i32> [#uses=1]
%r = add i32 %u, %v
ret i32 %r
}
define i32 @f() {
%u = call i32 @la() ; <i32> [#uses=1]
%v = call i32 @lb() ; <i32> [#uses=1]
%w = call i32 @lc() ; <i32> [#uses=1]
%r = add i32 %u, %v ; <i32> [#uses=1]
%s = add i32 %r, %w ; <i32> [#uses=1]
ret i32 %s
}

12
test/FrontendC/weak_constant.c Normal file
View File

@ -0,0 +1,12 @@
// RUN: %llvmgcc -S %s -O1 -o - | grep {ret.*123}
// Check for bug compatibility with gcc.
const int x __attribute((weak)) = 123;
int* f(void) {
return &x;
}
int g(void) {
return *f();
}