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

[Yingwei Zheng via llvm-commits]

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@@ -1207,6 +1207,50 @@ 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) {
+        if (OB1HasNSW && (match(B, m_APInt(C))) && (*C != -1))
+          return BinaryOperator::CreateSDiv(A, B);
+        if (auto *SV = simplifySDivInst(A, B, /*IsExact*/ true,
+                                        SQ.getWithInstruction(&I))) {
+          if (auto *CV = dyn_cast<Constant>(SV);
+              CV && !(isa<PoisonValue>(CV) || CV->containsPoisonElement()))
+            if (match(B, m_APInt(C)) && !C->abs().isPowerOf2() &&
+                C->abs().sqrt().sle((Ty->getScalarSizeInBits() - 2))) {
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dtcxzyw wrote:

Can you explain further about the condition? I think the condition here should be `!C->isSignMask()`. Please also add a negative test.



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