[Bug tree-optimization/109581] [13/14 Regression] Comparing with -HUGE_VAL wrong result

[daschuer at mixxx dot org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109581

--- Comment #3 from Daniel Schürmann  ---
I can confirm that -fno-finite-math-only fixes the issue. 

Since this a new behavior in GCC 13 and it is also a hard to find issue, which
took us many hours to dig it down, it would be nice tho have at least a warning
something like: 

warning: comparison of infinity constant is always false.

The issue is that this happens silently after a compiler update. It can cause
real live issues, but is only recognized by a chance in a big code base. 

Is there a use case of explicit compare with HUGE_VAL/-HUGE_VAL and than
disable it with -ffinite-math-only?

[Bug c/109581] New: Comparing with -HUGE_VAL wrong result

[daschuer at mixxx dot org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109581

Bug ID: 109581
   Summary: Comparing with -HUGE_VAL wrong result
   Product: gcc
   Version: unknown
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
  Assignee: unassigned at gcc dot gnu.org
  Reporter: daschuer at mixxx dot org
  Target Milestone: ---

Comparing with -HUGE_VAL gives the wrong result with gcc (GCC) 13.0.1 20230401
(Red Hat 13.0.1-0).

GCC 12.2 is and clang are not effected. 

This bug breaks Mixxx after compiling it on openSUSE Tumbleweed and Fedora 38 
https://github.com/mixxxdj/mixxx/issues/11483

The workaround is to store -HUGE_VAL as a volatile first. 

This is a minimal code that demonstrates the issue: 

#include 
#include 

int main(int num) {
long long rawInf = 0xfff0;
volatile  double inf = *(double*)(void*)

if (inf == -HUGE_VAL) {
puts("Success");
} else {
puts("Error");
}

return 0;
}


The following flags are used: 
-g -pipe -O3 -ffast-math -funroll-loops -fomit-frame-pointer -mtune=generic
-Wall -Wextra -Wfloat-conversion -Werror=return-type


Result 
GCC 12.2 and lower "Success"
GCC 13.0 "Error"

Details: https://godbolt.org/z/7bnb77hv4