[Bug target/30970] Register zeroing by xor N,N should be moved out of loop

[ubizjak at gmail dot com]

------- Comment #3 from ubizjak at gmail dot com  2007-02-26 19:51 -------
(In reply to comment #2)
> Shouldn't rtl invariant motion catch this?

It would be nice, but the problem is again in the fact that we lie to the
compiler about supported instructions. This one is not a valid x86 insn:

(insn 12 8 13 2 (set (mem:V4SI (symbol_ref:DI ("b") <var_decl 0x2aaaae15b000
b>) [3 S16 A128])
        (const_vector:V4SI [
                (const_int 0 [0x0])
                (const_int 0 [0x0])
                (const_int 0 [0x0])
                (const_int 0 [0x0])
            ])) 919 {*movv4si_internal} (nil)
    (nil))

This sequence is later split into pxor+store, unfortunatelly a bit late in the
game, after RTL optimizers have already done their job.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30970