[Bug target/91323] New: LTGT rtx produces UCOMISS instead of COMISS

[iii at linux dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91323

            Bug ID: 91323
           Summary: LTGT rtx produces UCOMISS instead of COMISS
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: iii at linux dot ibm.com
  Target Milestone: ---

I'm implementing signaling comparisons on S/390 and I'm trying to figure out
whether or not LTGT is supposed to be signaling.
I've decided to check what Intel does, and ran into what appears to be a bug.

Consider the following functions:

int f1(float a, float b) { return a < b || a > b; }
int f2(float a, float b) { return __builtin_isless(a, b) ||
__builtin_isgreater(a, b); }
int f3(float a, float b) { return __builtin_islessgreater(a, b); }

gcc creates LTGT rtx for f1 and UNEQ for f2 and f3.
However, for all 3 variants it then emits UCOMISS instruction.
I would expect f1 to be compiled to COMISS, since I believe that comparison
operators in C are supposed to be signaling.