[Bug tree-optimization/65425] New: code optimization leads to spurious FP exception

[p.vanhoof at oma dot be]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65425

            Bug ID: 65425
           Summary: code optimization leads to spurious FP exception
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: p.vanhoof at oma dot be

Created attachment 35035
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35035&action=edit
program that triggers the bug

Compile the attached test case with

gcc -O3 -ftrapping-math -fno-math-errno bug.c -lm

This produces no output. Running the executable will result in a spurious FP
exception. This happens with all gcc versions I tested since 4.7.0. Versions
4.6.4 and earlier work correctly, so this is a regression. It looks like the
code is being optimized with the implicit assumption that FP exceptions are not
trapped. However, using the -ftrapping-math flag should prevent such
optimizations (and should be the default as well).

% gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/gcc492/libexec/gcc/x86_64-unknown-linux-gnu/4.9.2/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc492/configure --prefix=/usr/local/gcc492
--enable-languages=c,c++,fortran
Thread model: posix
gcc version 4.9.2 (GCC)