[llvm-bugs] [Bug 43374] New: arm: silent == and != and __builtin_isnan compile to signaling compare

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43374

            Bug ID: 43374
           Summary: arm: silent == and != and __builtin_isnan compile to
                    signaling compare
           Product: new-bugs
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: szabolcs.nagy at arm.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

for

int foo(float x) {
  return __builtin_isnan(x) ? 0 : 1;
}
int bar(float x) {
  return x!=x ? 0 : 1;
}

i get

foo:
        vcmpe.f32       s0, s0
        vmrs    APSR_nzcv, fpscr
        mov     r0, #0
        movvc   r0, #1
        bx      lr
bar:
        vcmpe.f32       s0, s0
        vmrs    APSR_nzcv, fpscr
        mov     r0, #0
        movvc   r0, #1
        bx      lr

in standard conform compilation mode, i expected vcmp.f32 instead of vcmpe.f32.

in principle the difference is not observable if FENV_ACCESS is off, but since
clang does not support toggling that switch it must be assumed to be always on
for conforming behaviour and then != and is* operations must be non-signaling
(iso c annex f requirement).

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