[PATCH, i386] V4DF __builtin_shuffle

[Marc Glisse <marc dot glisse at inria dot fr>]

Hello,

this patch expands __builtin_shuffle for V4DF mode in at most 3 insn. It 
is simple and works really well, often generates only 2 insn. It is not 
very generic, because other modes don't have an instruction equivalent to 
vshufpd. For V8SF (and likely V4DI and V8SI with AVX2, but I still need to 
do that), my patch "default case" in PR 52607 seems more interesting.

I tried calling this new function after expand_vec_perm_vperm2f128_vblend 
(instead of before as in the patch), but it generated more instructions 
for some permutations, and never less. That function is still useful for 
V8SF though.

I bootstrapped gcc on a non-avx platform, compiled a program that tests 
all 4096 shuffles with -mavx/-mavx2, and ran the result using Intel's 
emulator (SDE).

There are still a few V4DF permutations that don't generate an optimal 
sequence (3 insn instead of 2), but not that many I think. Of course, I am 
assuming a constant cost of 1 per insn, which is completely false, but 
seems like a sensible first approximation.

(note that I can't commit)


2012-04-17  Marc Glisse  <marc.glisse@inria.fr>

	PR target/502607
	* config/i386/i386.c (ix86_expand_vec_perm_const): Move code to ...
	(canonicalize_perm): ... new function.
	(expand_vec_perm_2vperm2f128_vshuf): New function.
	(ix86_expand_vec_perm_const_1): Call it.

--
Marc Glisse

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