[Bug target/52607] v4df __builtin_shuffle with {0,2,1,3} or {1,3,0,2}

[marc.glisse at normalesup dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52607

--- Comment #28 from Marc Glisse <marc.glisse at normalesup dot org> 2012-04-11 
16:48:47 UTC ---
A difficulty I hadn't foreseen is that the code that canonicalizes permutations
(and in particular checks if one of the operands is unused) is in
ix86_expand_vec_perm_const. So if I ask expand_vec_perm_1 to generate the
2-operand 0,1,2,3 permutation, it will happily generate vperm2f128 with
immediate 16 without noticing that it is the identity on the first operand. I
should probably move that code into its own function so I can call it before
expand_vec_perm_1.