[llvm] [InstCombine] Fold zext(X) + C2 pred C -> X + C3 pred C4 (PR #110511)

[Yingwei Zheng via llvm-commits]

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@@ -3168,6 +3168,31 @@ Instruction *InstCombinerImpl::foldICmpAddConstant(ICmpInst &Cmp,
                         Builder.CreateAdd(X, ConstantInt::get(Ty, *C2 - C - 1)),
                         ConstantInt::get(Ty, ~C));
 
+  // zext(V) + C2 pred C -> V + C3 pred' C4
+  Value *V;
+  if (match(X, m_ZExt(m_Value(V)))) {
+    Type *NewCmpTy = V->getType();
+    unsigned CmpBW = Ty->getScalarSizeInBits();
+    unsigned NewCmpBW = NewCmpTy->getScalarSizeInBits();
+    if (shouldChangeType(Ty, NewCmpTy)) {
+      if (auto ZExtCR = CR.exactIntersectWith(ConstantRange(
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dtcxzyw wrote:

We need a new ConstantRange API to convert ranges for `zext(V)` to ranges for `V`.
For example, we can convert `zext(i8 X to i32) - 255 u< -4` to `X + 1 u< -4`. But current implementation cannot achieve this.


https://github.com/llvm/llvm-project/pull/110511