[llvm] [X86][AVX512] Use comx for compare (PR #113098)

[Phoebe Wang via llvm-commits]

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@@ -49520,6 +49520,15 @@ static SDValue combineCompareEqual(SDNode *N, SelectionDAG &DAG,
           // FIXME: need symbolic constants for these magic numbers.
           // See X86ATTInstPrinter.cpp:printSSECC().
           unsigned x86cc = (cc0 == X86::COND_E) ? 0 : 4;
+
+          // VCOMXSS simplifies conditional code sequence into single setcc node.
+          // Earlier until COMI, it required upto 2 SETCC's to test CC.
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phoebewang wrote:

I don't understand the logic here. Why do we require 2 CC for comx? I don't see a test case using 2 CC. Can we just return `SDValue()` to break combine?

https://github.com/llvm/llvm-project/pull/113098