Add a rather pointless InstructionSimplify transform, inspired by recent constant
folding improvements: if P points to a type of size zero, turn "gep P, N" into "P".
More generally, if a gep index type has size zero, instcombine could replace the
index with zero, but that is not done here.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119942 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 97612f4..6b51b22 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -18,6 +18,7 @@
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/Support/ValueHandle.h"
+#include "llvm/Target/TargetData.h"
using namespace llvm;
using namespace llvm::PatternMatch;
@@ -698,11 +699,18 @@
//if (isa<UndefValue>(Ops[0]))
// return UndefValue::get(GEP.getType());
- // getelementptr P, 0 -> P.
- if (NumOps == 2)
+ if (NumOps == 2) {
+ // getelementptr P, 0 -> P.
if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
if (C->isZero())
return Ops[0];
+ // getelementptr P, N -> P if P points to a type of zero size.
+ if (TD) {
+ const Type *Ty = cast<PointerType>(Ops[0]->getType())->getElementType();
+ if (Ty->isSized() && !TD->getTypeAllocSize(Ty))
+ return Ops[0];
+ }
+ }
// Check to see if this is constant foldable.
for (unsigned i = 0; i != NumOps; ++i)