[llvm] [InstCombine] optimize unnecessary sext instruction with add + cmp (PR #152291)

[Nikita Popov via llvm-commits]

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@@ -6381,6 +6381,36 @@ Instruction *InstCombinerImpl::foldICmpWithZextOrSext(ICmpInst &ICmp) {
   return new ICmpInst(CmpInst::ICMP_SLT, X, Constant::getNullValue(SrcTy));
 }
 
+Instruction *InstCombinerImpl::foldICmpWithSextAndAdd(ICmpInst &ICmp) {
+  Value *X;
+  ConstantInt *Y, *Z;
+  // Match the pattern: icmp ult (add (sext X), Y), Z
+  // where X is a value, Y and Z are integer constants
+  // icmp ult (add(sext(X), Y)), Z  -> icmp ult (add(X, Y)), Z
+  if (match(&ICmp, m_SpecificICmp(CmpInst::ICMP_ULT,
+                            m_Add(m_SExt(m_Value(X)), m_ConstantInt(Y)),
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nikic wrote:

m_ConstantInt -> m_APInt and then work on APInt instead of int64_t returned by getSExtValue().

https://github.com/llvm/llvm-project/pull/152291