http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54900



Jakub Jelinek <jakub at gcc dot gnu.org> changed:



           What    |Removed                     |Added

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                 CC|                            |aldyh at gcc dot gnu.org,

                   |                            |jakub at gcc dot gnu.org



--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-10-11 
11:59:14 UTC ---

This is ifcvt.c in action.

This is the if (!set_b && MEM_P (orig_x)) case where we already do some checks:

if (noce_mem_write_may_trap_or_fault_p (orig_x)) return FALSE; and

if (!noce_can_store_speculate_p (test_bb, orig_x)) return FALSE;

I'd say noce_can_store_speculate_p is buggy, it uses

          if (memory_modified_in_insn_p (mem, insn))

            return true;

but memory_modified_in_insn_p is pessimistic, it doesn't tell whether mem is

surely set, but whether it might be set.  I guess it would need to use

note_stores that would just do rtx_equal_p on the addresses or similarly prove

it is surely (and unconditionally) written.  So even note_stores might not be

the right thing, perhaps just looking at single_set SET_DEST.  And avoiding

inline asm, that doesn't have to store unconditionally.

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