Don't load values out of global constants with weak

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).

llvm-svn: 67407

3 files changed, 8 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 4a7f4c74f33..10671cd908b 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -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()))
diff --git a/llvm/lib/Transforms/Scalar/SCCP.cpp b/llvm/lib/Transforms/Scalar/SCCP.cpp
index 7adc80fb5a5..a49bcc84547 100644
--- a/llvm/lib/Transforms/Scalar/SCCP.cpp
+++ b/llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -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);
diff --git a/llvm/lib/Transforms/Utils/CloneFunction.cpp b/llvm/lib/Transforms/Utils/CloneFunction.cpp
index 59211028f31..5dc2d1cdc3a 100644
--- a/llvm/lib/Transforms/Utils/CloneFunction.cpp
+++ b/llvm/lib/Transforms/Utils/CloneFunction.cpp
@@ -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);