[llvm] [KnownFPClass] Fix fsub input denormal handling (PR #225605)

[Eric Ross via llvm-commits]

================
@@ -341,8 +341,18 @@ define float @fsub_p0_commute_ieee_daz(float %arg0) #2 {
   ret float %sub
 }
 
-define float @fsub_n0_commute_ieee_daz(float %arg0) #1 {
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ZERICO2005 wrote:

The test name and attribute value disagree, so I split this test into two.
```
attributes #1 = { denormal_fpenv(preservesign|ieee) }
attributes #2 = { denormal_fpenv(ieee|preservesign) }
```

https://github.com/llvm/llvm-project/pull/225605