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

[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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mahesh-attarde wrote:

```
Optimized type-legalized selection DAG: %bb.0 'oeq:'
SelectionDAG has 11 nodes:
  t0: ch,glue = EntryToken
      t2: f32,ch = CopyFromReg t0, Register:f32 %0
      t4: f32,ch = CopyFromReg t0, Register:f32 %1
    t14: i8 = setcc t2, t4, setoeq:ch
  t10: ch,glue = CopyToReg t0, Register:i8 $al, t14
  t11: ch = X86ISD::RET_GLUE t10, TargetConstant:i32<0>, Register:i8 $al, t10:1

Legalized selection DAG: %bb.0 'oeq:'
SelectionDAG has 15 nodes:
  t0: ch,glue = EntryToken
      t24: i8 = X86ISD::SETCC TargetConstant:i8<4>, t20
      t22: i8 = X86ISD::SETCC TargetConstant:i8<11>, t20
    t19: i8 = and t24, t22
  t10: ch,glue = CopyToReg t0, Register:i8 $al, t19
    t2: f32,ch = CopyFromReg t0, Register:f32 %0
    t4: f32,ch = CopyFromReg t0, Register:f32 %1
  t20: i32 = X86ISD::FCMP t2, t4
  t11: ch = X86ISD::RET_GLUE t10, TargetConstant:i32<0>, Register:i8 $al, t10:1
```
If i understand correctly you are asking to remove t19, t22 and t24, is that correct?

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