[Bug middle-end/40547] New: comparison in lhs of ?: incorrectly converted to unsigned min

[mikpe at it dot uu dot se]

Compiling this test program with gcc-4.4-20090623 fails with a linker error:

> cat pr39867-redux.c
int main (void)
{
  int exp = -1;
  /* Wrong folding of the LHS to an unsigned MIN leads to 2 != 4294967295. */
  if ((exp < 2 ? (unsigned int) exp : 2U) != -1U)
    link_error ();
  return 0;
}
> gcc -O2 pr39867-redux.c
/tmp/ccwtpmSD.o: In function `main':
pr39867-redux.c:(.text+0x7): undefined reference to `link_error'
collect2: ld returned 1 exit status

This is a regression from gcc-4.3.3 and earlier releases.

The test case is a variant of PR39867, which got fixed. That bug report was
about fold-const.c turning a ?: into MAX and wrongly changing a signed compare
to an unsigned compare in the process. There are additional cases that turn ?:
into MIN, but they weren't considered or fixed.

I'll attach the test case and a proposed fix.


-- 
           Summary: comparison in lhs of ?: incorrectly converted to
                    unsigned min
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mikpe at it dot uu dot se
  GCC host triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40547