[llvm] [InstCombine] fold (A + B - C == B) -> (A == C). (PR #76129)

[Yingwei Zheng via llvm-commits]

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@@ -4547,6 +4547,48 @@ static Instruction *foldICmpXorXX(ICmpInst &I, const SimplifyQuery &Q,
   return nullptr;
 }
 
+// extract common factors like ((A + B) - C == B) -> (A - C == 0)
+Instruction *InstCombinerImpl::foldICmpWithCommonFactors(ICmpInst &Cmp,
+                                                         BinaryOperator *LBO,
+                                                         Value *RHS) {
+  const CmpInst::Predicate Pred = Cmp.getPredicate();
+  if (!ICmpInst::isEquality(Pred))
+    return nullptr;
+
+  if (LBO->getOpcode() != Instruction::Add &&
+      LBO->getOpcode() != Instruction::Sub)
+    return nullptr;
+
+  SmallVector<BinaryOperator *, 16> worklist;
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dtcxzyw wrote:

What is the compile-time impact of the worklist based algorithm? Should we set a maximum size of the add-sub chain?

https://github.com/llvm/llvm-project/pull/76129