[PATCH] D143191: DAG: Handle inversion of fcSubnormal | fcZero

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


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Comment at: llvm/test/CodeGen/X86/is_fpclass.ll:894-901
+; CHECK-32-NEXT:    flds {{[0-9]+}}(%esp)
+; CHECK-32-NEXT:    fldz
+; CHECK-32-NEXT:    fucompp
+; CHECK-32-NEXT:    fnstsw %ax
+; CHECK-32-NEXT:    # kill: def $ah killed $ah killed $ax
+; CHECK-32-NEXT:    sahf
+; CHECK-32-NEXT:    setp %cl
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sepavloff wrote:
> arsenm wrote:
> > sepavloff wrote:
> > > This code looks incorrect. The argument is compared against 0.0 and the result is true if the comparison is unordered or not equal.
> > Looks like I broke the inverted case and ended up fixing it in one of my later patches
> Not sure if x87 has DAZ mode. Corresponding flag is in MXCSR only and it is not clear if MXCSR affects operations in x87. @jcranmer-intel, could you please clarify this point?
The attribute says codegen can assume this. If the hardware doesn't actually support the mode this is just undefined usage which doesn't matter


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  https://reviews.llvm.org/D143191/new/

https://reviews.llvm.org/D143191