[llvm] [InstCombine] Simplification for (-a * b) / (a * b) and (a - b) / (b - a). (PR #71768)

[via llvm-commits]

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@@ -1544,6 +1544,20 @@ Instruction *InstCombinerImpl::visitSDiv(BinaryOperator &I) {
     }
   }
 
+  // -(X * Y) / (X * Y) --> -1
+  if ((match(Op0, m_Neg(m_c_Mul(m_Value(X), m_Value(Y)))) &&
+       match(Op1, m_c_Mul(m_Specific(X), m_Specific(Y)))) ||
+      (match(Op0, m_c_Mul(m_Value(X), m_Value(Y))) &&
+       match(Op1, m_Neg(m_c_Mul(m_Specific(X), m_Specific(Y)))))) {
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goldsteinn wrote:

You could also:
1) check knownbits to see that X/Y are not INT_MIN
2) You could also handle `((-a) * b) / (a * b)` (which doesn't get canonicalized to `(-(a * b)) / (a * b)`)

https://github.com/llvm/llvm-project/pull/71768