------- Comment #3 from hjl dot tools at gmail dot com 2010-02-25 15:06 ------- We expand
D.3242_4 = __builtin_ia32_vec_perm_v4si (D.3241_3, D.3240_2, { 4, 1, 2, 3 }); into (insn 27 24 28 3 x.i:22 (set (subreg:V8HI (reg:V4SI 75) 0) (vec_merge:V8HI (subreg:V8HI (reg:V4SI 75) 0) (subreg:V8HI (reg:V4SI 75) 0) (const_int 3 [0x3]))) -1 (nil)) (insn 28 27 29 3 x.i:22 (set (reg:V4SI 60 [ D.3242 ]) (reg:V4SI 75)) -1 (nil)) But reg 75 is never set. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43175