http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50251
--- Comment #14 from vries at gcc dot gnu.org 2011-09-02 10:28:52 UTC ---
> but for some reason it doesn't trigger?
The bb containing the __builtin_stack_restore has 2 successors:
...
<bb 6>:
D.2099_18 = MEM[(int *)&D.2129][5]{lb: 0 sz: 4};
__builtin_stack_restore (saved_stack.3_5);
if (D.2099_18 != 15)
goto <bb 7>;
else
goto <bb 8>;
...
This case doesn't fall into the cases described in the header comment.
...
/* Try to optimize out __builtin_stack_restore. Optimize it out
if there is another __builtin_stack_restore in the same basic
block and no calls or ASM_EXPRs are in between, or if this block's
only outgoing edge is to EXIT_BLOCK and there are no calls or
ASM_EXPRs after this __builtin_stack_restore. */
...
It hits this piece of code in optimize_stack_restore and returns, so it doesn't
reach second_stack_restore:
...
/* Allow one successor of the exit block, or zero successors. */
switch (EDGE_COUNT (bb->succs))
{
case 0:
break;
case 1:
if (single_succ_edge (bb)->dest != EXIT_BLOCK_PTR)
return NULL_TREE;
break;
default:
return NULL_TREE;
}
second_stack_restore:
...
For the stack-save-restore.c, if I declare p inside the function, cse creates a
(set (sp) (sp)), which is eliminated.
But for the 20010209-1.c example, that doesn't happen.
