If a GEP index simply advances by multiples of a type of zero size,
then replace the index with zero.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119974 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index e617ff2..4b6320b 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -714,7 +714,7 @@
// getelementptr P, N -> P if P points to a type of zero size.
if (TD) {
const Type *Ty = PtrTy->getElementType();
- if (Ty->isSized() && !TD->getTypeAllocSize(Ty))
+ if (Ty->isSized() && TD->getTypeAllocSize(Ty) == 0)
return Ops[0];
}
}
diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index 89d5bfb..cfc4182 100644
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -523,25 +523,35 @@
Value *PtrOp = GEP.getOperand(0);
- // Eliminate unneeded casts for indices.
+ // Eliminate unneeded casts for indices, and replace indices which displace
+ // by multiples of a zero size type with zero.
if (TD) {
bool MadeChange = false;
- unsigned PtrSize = TD->getPointerSizeInBits();
-
+ const Type *IntPtrTy = TD->getIntPtrType(GEP.getContext());
+
gep_type_iterator GTI = gep_type_begin(GEP);
for (User::op_iterator I = GEP.op_begin() + 1, E = GEP.op_end();
I != E; ++I, ++GTI) {
- if (!isa<SequentialType>(*GTI)) continue;
-
- // If we are using a wider index than needed for this platform, shrink it
- // to what we need. If narrower, sign-extend it to what we need. This
- // explicit cast can make subsequent optimizations more obvious.
- unsigned OpBits = cast<IntegerType>((*I)->getType())->getBitWidth();
- if (OpBits == PtrSize)
- continue;
-
- *I = Builder->CreateIntCast(*I, TD->getIntPtrType(GEP.getContext()),true);
- MadeChange = true;
+ // Skip indices into struct types.
+ const SequentialType *SeqTy = dyn_cast<SequentialType>(*GTI);
+ if (!SeqTy) continue;
+
+ // If the element type has zero size then any index over it is equivalent
+ // to an index of zero, so replace it with zero if it is not zero already.
+ if (SeqTy->getElementType()->isSized() &&
+ TD->getTypeAllocSize(SeqTy->getElementType()) == 0)
+ if (!isa<Constant>(*I) || !cast<Constant>(*I)->isNullValue()) {
+ *I = Constant::getNullValue(IntPtrTy);
+ MadeChange = true;
+ }
+
+ if ((*I)->getType() != IntPtrTy) {
+ // If we are using a wider index than needed for this platform, shrink
+ // it to what we need. If narrower, sign-extend it to what we need.
+ // This explicit cast can make subsequent optimizations more obvious.
+ *I = Builder->CreateIntCast(*I, IntPtrTy, true);
+ MadeChange = true;
+ }
}
if (MadeChange) return &GEP;
}