[llvm] [InstCombine] fold `sub(zext(ptrtoint), zext(ptrtoint))` (PR #115369)

[Nikolay Panchenko via llvm-commits]

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@@ -2631,6 +2631,21 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
                                                /* IsNUW */ false))
       return replaceInstUsesWith(I, Res);
 
+  if (match(Op0, m_ZExt(m_PtrToInt(m_Value(LHSOp)))) &&
+      match(Op1, m_ZExtOrSelf(m_PtrToInt(m_Value(RHSOp))))) {
+    if (auto *GEP = dyn_cast<GEPOperator>(LHSOp)) {
+      if (GEP->getPointerOperand() == RHSOp) {
+        if (GEP->hasNoUnsignedWrap() || GEP->hasNoUnsignedSignedWrap()) {
+          Value *Offset = EmitGEPOffset(GEP);
+          Value *Res = GEP->hasNoUnsignedWrap()
+                           ? Builder.CreateZExt(Offset, I.getType())
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npanchen wrote:

it's only possible if both nowrap flags are set: https://alive2.llvm.org/ce/z/QXHkTH

https://github.com/llvm/llvm-project/pull/115369