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

[Yingwei Zheng via llvm-commits]

================
@@ -1207,6 +1207,34 @@ 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(B, m_APInt(C))) &&
+          (*C != -1))
+        return BinaryOperator::CreateSDiv(A, B);
+      if (!IsSigned && OB0HasNUW && OB1HasNUW) {
----------------
dtcxzyw wrote:

Looks like the new version of your patch cannot handle the following pattern:
```
define i4 @src(i4 %a) {
  %add4 = mul i4 %a, 3
  %add5 = mul nuw i4 %a, 6
  %div = udiv i4 %add5, %add4
  ret i4 %div
}

define i4 @tgt(i4 %a) {
  ret i4 2
}
```
Alive2: https://alive2.llvm.org/ce/z/27Ei4q


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