[Bug middle-end/106805] New: Undue optimisation of floating-point comparisons

[fxcoudert at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106805

            Bug ID: 106805
           Summary: Undue optimisation of floating-point comparisons
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fxcoudert at gcc dot gnu.org
  Target Milestone: ---

With current gcc trunk, on x86_64-linux:

$ cat a.c
#include <math.h>
#include <stdio.h>
#include <fenv.h>

void foo (void) {
 if (fetestexcept (FE_INVALID) & FE_INVALID)
   printf("Invalid raised\n");
 feclearexcept (FE_ALL_EXCEPT);
}

static inline int iseqsig(float x, float y) { return (x >= y && x <= y); }

int main (void) {
 float x = __builtin_nanf("");
 float y;

 printf("%d\n", iseqsig(__builtin_nanf(""), 1.));
 foo();

 printf("%d\n", iseqsig(x, __builtin_inff()));
 foo();
}

$ ./bin/gcc a.c -lm -fno-unsafe-math-optimizations -frounding-math
-fsignaling-nans -O0 && ./a.out
0
Invalid raised
0
Invalid raised

$ ./bin/gcc a.c -lm -fno-unsafe-math-optimizations -frounding-math
-fsignaling-nans -O1 && ./a.out
0
0


The comparisons should raise FE_INVALID in all cases, and not be optimised
away.