[InstSimplify] Fold gep (gep V, C), (sub 0, V) to C
llvm-svn: 277952
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 69c60eb..e6aed6d 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3645,6 +3645,26 @@
}
}
+ // gep (gep V, C), (sub 0, V) -> C
+ if (Q.DL.getTypeAllocSize(LastType) == 1 &&
+ all_of(Ops.slice(1).drop_back(1),
+ [](Value *Idx) { return match(Idx, m_Zero()); })) {
+ unsigned PtrWidth =
+ Q.DL.getPointerSizeInBits(Ops[0]->getType()->getPointerAddressSpace());
+ if (Q.DL.getTypeSizeInBits(Ops.back()->getType()) == PtrWidth) {
+ APInt BasePtrOffset(PtrWidth, 0);
+ Value *StrippedBasePtr =
+ Ops[0]->stripAndAccumulateInBoundsConstantOffsets(Q.DL,
+ BasePtrOffset);
+
+ if (match(Ops.back(),
+ m_Sub(m_Zero(), m_PtrToInt(m_Specific(StrippedBasePtr))))) {
+ auto *CI = ConstantInt::get(GEPTy->getContext(), BasePtrOffset);
+ return ConstantExpr::getIntToPtr(CI, GEPTy);
+ }
+ }
+ }
+
// Check to see if this is constant foldable.
for (unsigned i = 0, e = Ops.size(); i != e; ++i)
if (!isa<Constant>(Ops[i]))