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.
