[llvm] [InstCombine] simplify `(X * C0) / (X * C1)` into `C0 / C1`. (PR #73204)

[via llvm-commits]

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@@ -1207,6 +1207,45 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
     }
   }
 
+  // (X * Y) / (X * Z) --> Y / X (and commuted variants)
+  if (match(Op0, m_Mul(m_Value(X), m_Value(Y)))) {
+    auto OB0HasNSW = cast<OverflowingBinaryOperator>(Op0)->hasNoSignedWrap();
+    auto OB0HasNUW = cast<OverflowingBinaryOperator>(Op0)->hasNoUnsignedWrap();
+
+    auto CreateDivOrNull = [&](Value *A, Value *B) -> Instruction * {
+      auto OB1HasNSW = cast<OverflowingBinaryOperator>(Op1)->hasNoSignedWrap();
+      auto OB1HasNUW =
+          cast<OverflowingBinaryOperator>(Op1)->hasNoUnsignedWrap();
+      const APInt *C;
+      if (IsSigned && OB0HasNSW && OB1HasNSW && (match(A, m_APInt(C))) &&
+          (*C != -1 ||
+           *C != APInt::getSignedMinValue(Ty->getScalarSizeInBits())))
+        return BinaryOperator::CreateSDiv(A, B);
+      if (!IsSigned && OB0HasNUW && OB1HasNUW) {
+        return BinaryOperator::CreateUDiv(A, B);
+      };
+      if (isa<Constant>(A) && isa<Constant>(B)) {
+        if (IsSigned && OB0HasNSW) {
+          return BinaryOperator::CreateSDiv(A, B);
+        }
+        if (!IsSigned && OB0HasNUW) {
+          return BinaryOperator::CreateUDiv(A, B);
+        };
+      };
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Z572 wrote:

Maybe this is better? https://alive2.llvm.org/ce/z/HL3K6G

https://github.com/llvm/llvm-project/pull/73204