[Bug tree-optimization/48973] [4.3/4.4/4.5/4.6/4.7 Regression] Inliner bug with one-bit (1-bit) bitfield

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48973

--- Comment #2 from Jakub Jelinek jakub at gcc dot gnu.org 2011-05-12 
07:20:30 UTC ---
extern void abort (void);
struct S { int f : 1; } s;
int v = -1;

void
foo (void)
{
  s.f = (v  1)  0;
}

void
bar (unsigned int x)
{
  if (x != -1U)
abort ();
}

int
main ()
{
  foo ();
  bar (s.f);
  return 0;
}

[Bug tree-optimization/48973] [4.3/4.4/4.5/4.6/4.7 Regression] Inliner bug with one-bit (1-bit) bitfield

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48973

--- Comment #3 from Jakub Jelinek jakub at gcc dot gnu.org 2011-05-12 
07:29:37 UTC ---
extern void abort (void);
struct S { int f : 1; } s;
int v = -1;

void
foo (unsigned int x)
{
  if (x != -1U)
abort ();
}

int
main ()
{
  s.f = (v  1)  0;
  foo (s.f);
  return 0;
}

Smaller testcase which failed already in 4.2, apparently introduced in between
r97500 and r98750.

[Bug tree-optimization/48973] [4.3/4.4/4.5/4.6/4.7 Regression] Inliner bug with one-bit (1-bit) bitfield

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48973

--- Comment #4 from Jakub Jelinek jakub at gcc dot gnu.org 2011-05-12 
07:36:07 UTC ---
And even more reduced:
extern void abort (void);
struct S { int f : 1; } s;
int v = -1;

int
main ()
{
  s.f = (v  1)  0;
  if ((unsigned int) s.f != -1U)
abort ();
  return 0;
}

[Bug tree-optimization/48973] [4.3/4.4/4.5/4.6/4.7 Regression] Inliner bug with one-bit (1-bit) bitfield

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48973

Jakub Jelinek jakub at gcc dot gnu.org changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2011.05.12 07:19:50
 CC||jakub at gcc dot gnu.org
  Known to work||4.2.3
   Target Milestone|--- |4.3.6
Summary|Inliner bug with one-bit|[4.3/4.4/4.5/4.6/4.7
   |(1-bit) bitfield|Regression] Inliner bug
   ||with one-bit (1-bit)
   ||bitfield
 Ever Confirmed|0   |1
  Known to fail||4.3.3, 4.6.0, 4.7.0

--- Comment #1 from Jakub Jelinek jakub at gcc dot gnu.org 2011-05-12 
07:19:50 UTC ---
Confirmed, started in between r11 and r112000, but strangely works in 4.2
which has branched off in r117923.  Looking into it.

[Bug tree-optimization/48973] [4.3/4.4/4.5/4.6/4.7 Regression] Inliner bug with one-bit (1-bit) bitfield

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48973

--- Comment #5 from Jakub Jelinek jakub at gcc dot gnu.org 2011-05-12 
08:29:09 UTC ---
Even smaller:

extern void abort (void);
struct S { int f : 1; } s;
int v = -1;

int
main ()
{
  s.f = v  0;
  if ((unsigned int) s.f != -1U)
abort ();
  return 0;
}

I'd say the bug is during expansion of a comparison with signed 1 bit type. 
Then the comparison needs to result 0 / -1 instead of 0 / 1.  I think it would
be difficult to adjust all the conditional expansion to handle this very rare
special case, so probably it will be better to expand such conditionals as
if it was unsigned:1 or unsigned char typed comparison, followed by cast from
that type to signed:1.