When building 64 bit with an optimization setting of -O2, -O3, or -Os, some
binary comparisons with nan values fail to produce false. All comparisons (==,
>, <, etc) where one (or both) of the two values is nan should produce false.
There are no warnings or other error messages during compilation. The attached
test demonstrates the error with the final assert failing. The max() function
should return the maximum of the two values, ignoring nans. i.e., max(5, nan)
should be 5. This fails with gcc3.4.6 -O2 -m64.
Strangely, switching the order of the final portion of the return to something
like:
return (a > b ? a : (b > a ? b : (isNaN(b) ? a : b)));
causes it to work.
Also, replacing isNaN() with a call to the slower, non-inline isnan() also
makes the function work.
--
Summary: Incorrect optization with nan values
Product: gcc
Version: 3.4.6
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: scott at minsters dot us
GCC build triplet: x86_64-redhat-linux
GCC host triplet: x86_64-redhat-linux
GCC target triplet: x86_64-redhat-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31542
