https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108355
--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #11)
> (In reply to Hans-Peter Nilsson from comment #10)
> > (In reply to Richard Biener from comment #9)
> > > gcc.dg/tree-ssa/ssa-fre-104.c has been XFAILed.
> >
> > Any obvious target-specific reason for this to XPASS on cris-elf, m68k-linux
> > and pru-elf?
> >
> > (per recent gcc-testresults posts)
>
> Most likely because
> int e[][1] = {0, 0, 0, 0, 0, 1};
>
> Is done as a copy from a const static decl vs done via stores to e[i][0].
>
> Maybe do s/5/2/ and change the number of elements down to 3 for the array
> and you will hit the issue again on those targets.
Huh, most likely, but I don't see how that would help ... that should
make it _fail_ to optimize this ...
So checking cris-elf I see
<bb 2> :
e[0][0] = 0;
e[1][0] = 0;
e[2][0] = 0;
e[3][0] = 0;
e[4][0] = 0;
e[5][0] = 1;
<bb 3> :
bar25_ ();
a.0_1 = a;
_2 = e[5][a.0_1];
if (_2 != 0)
goto <bb 5>; [INV]
else
goto <bb 4>; [INV]
<bb 4> :
a.1_3 = a;
e[a.1_3][0] = 0;
foo ();
goto <bb 3>; [INV]
before FRE, the same IL as on x86_64. A FRE dump diff reveals
Setting value number of a.0_1 to a.0_1 (changed)
Making available beyond BB3 a.0_1 for value a.0_1
Value numbering stmt = _2 = e[5][a.0_1];
-Skipping possible redundant definition e[5][0] = 1;
-Setting value number of _2 to _2 (changed)
-Using extra use virtual operand .MEM_5
-Making available beyond BB3 _2 for value _2
+Setting value number of _2 to 1 (changed)
that's exactly the reason for the regression - we're now trying to skip
the definition on x86_64. And we can do so there because of the alignment
of 'e' which on cris seems to be less than the size of 'int' (int is
aligned to 1 byte but its size is still 4 bytes).
So
int a;
int *b = &a;
int **c = &b;
int d;
void bar25_(void);
void foo(void);
int main() {
int __attribute__((aligned(sizeof(int)))) e[][1] = {0, 0, 0, 0, 0, 1};
for (;;) {
bar25_();
/* We should optimistically treat a == 0 because of the bounds of
the object. */
if (e[5][a])
break;
e[a][0] = 0;
foo();
}
*c = &d;
}
also fails on cris. Let me update the testcase.
