http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50176
Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |ebotcazou at gcc dot
| |gnu.org
--- Comment #11 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-01-10
22:03:43 UTC ---
> thus there is a store between the load and the zero_extend (and combine
> only combines forward, not backward):
>
> /* Verify that I2 and I1 are valid for combining. */
> if (! can_combine_p (i2, i3, i0, i1, NULL_RTX, NULL_RTX, &i2dest, &i2src)
>
> already fails.
combine is a peephole optimizer so you cannot ask it to combine insns with 8
other intervening insns between them. It looks like we have a real problem
with extensions though and the good approach (backward combining) appears to be
that of the REE pass, but it's too limited for the time being.
