[llvm] [llvm] Don't combine repeated subnormal divisors (PR #149333)

[Eli Friedman via llvm-commits]

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@@ -18235,6 +18235,16 @@ SDValue DAGCombiner::combineRepeatedFPDivisors(SDNode *N) {
   if (N0CFP && (N0CFP->isExactlyValue(1.0) || N0CFP->isExactlyValue(-1.0)))
     return SDValue();
 
+  // Skip if we have subnormals, multiplying with the reciprocal will introduce
+  // infinities.
+  ConstantFPSDNode *N1CFP = isConstOrConstSplatFP(N1, /* AllowUndefs */ true);
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efriedma-quic wrote:

Right, there's no way to consistently disable the transform for subnormals without completely disabling arcp for non-constant denominators.  I don't really want to deal with the bug report that SimplifyCFG is illegally transforming floating-point code...

https://github.com/llvm/llvm-project/pull/149333