[llvm] [InstCombine] Add fold `(x * z) % (y * z) == 0` -> `x % y == 0` (PR #171655)

[Nikita Popov via llvm-commits]

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@@ -2735,6 +2735,61 @@ Instruction *InstCombinerImpl::foldICmpSRemConstant(ICmpInst &Cmp,
   return new ICmpInst(ICmpInst::ICMP_UGT, And, ConstantInt::get(Ty, SignMask));
 }
 
+/// Fold icmp {eq, ne} ({us}rem (mul n{us}w XZ, YZ)), 0 ->
+/// icmp {eq, ne} ({us}rem (mul n{us}w X, Y)), 0
+Instruction *InstCombinerImpl::foldICmpRemConstant(ICmpInst &Cmp,
+                                                   BinaryOperator *Rem,
+                                                   const APInt &C) {
+  assert((Rem->getOpcode() == Instruction::SRem ||
+          Rem->getOpcode() == Instruction::URem) &&
+         "foldICmpRemConstant is only for srem/urem.");
+
+  if (!C.isZero() || !Rem->hasOneUse())
+    return nullptr;
+
+  const ICmpInst::Predicate Pred = Cmp.getPredicate();
+  if (Pred != ICmpInst::ICMP_EQ && Pred != ICmpInst::ICMP_NE)
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nikic wrote:

Use `Cmp.isEquality()` instead.

https://github.com/llvm/llvm-project/pull/171655