[Bug c++/86586] New: [6/7/8/9 Regression] -Wsign-compare affects code generation

[amonakov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86586

            Bug ID: 86586
           Summary: [6/7/8/9 Regression] -Wsign-compare affects code
                    generation
           Product: gcc
           Version: 6.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amonakov at gcc dot gnu.org
            Blocks: 86518
  Target Milestone: ---

void f ()
{
  __builtin_cpu_supports ("avx2") && __builtin_cpu_supports ("ssse3");
}

ICEs with 'g++ -std=c++98 -fcompare-debug=-Wsign-compare'. This is minimized
from mv1.C in the testsuite.

I know it's inconvenient that this test depends on an x86-specific builtin, but
unfortunately I don't see other tests failing (apart from cp/mangle.c
miscomparing on bootstrap with/without the warning).

This may be similar to PR 86567: there's a use of maybe_constant_value guarded
by warn_sign_compare.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86518
[Bug 86518] Strengthen bootstrap comparison by not enabling warnings at stage3