------- Comment #8 from jakub at gcc dot gnu dot org  2010-09-14 17:15 -------
I've looked at the combiner with the second patch, but I'm afraid this isn't
fixable in the combiner easily.  While combiner is able for i3
(set (reg:V2DI res) (plus:V2DI (reg:V2DI temp) (mem:V2DI (symbol_ref:P t))))
, i2
(set (reg:V2DI temp) (minus:V2DI zero) (mem:V2DI (reg:V2DI a)))
and i1
(set (reg:V2DI zero) (const_vector:V2DI [0 0]))
to figure this is
(set (reg:V2DI res) (minus:V2DI (mem:V2DI (symbol_ref:P t)) (reg:V2DI a))
(plus repeating i1, as its result is not dead), this pattern doesn't match
as minus obviously isn't commutative and combiner doesn't try to make 3 insns
out of 3.  So I'd prefer if we could either apply the first patch, or try TER
on the PLUS_EXPR to see if the second operand isn't negation and expand it as
MINUS_EXPR, even when MINUS_EXPR isn't allowed on such arguments in GIMPLE.



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