https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109610
--- Comment #2 from Hongtao.liu <crazylht at gmail dot com> --- testcase: #ifndef TYPE #define TYPE vector double #endif struct foo { TYPE a, b, c, d; }; /* Make sure we don't use direct moves to get stuff into GPR registers. */ void gpr (struct foo *p) { TYPE x = p->c; __asm__ (" # reg = %0" : "+r" (x)); p->b = x; } Here's dump in ira. ------------- a2(r117,l0) costs: BASE_REGS:12000,12000 GENERAL_REGS:12000,12000 FLOAT_REGS:0,0 ALTIVEC_REGS:0,0 VSX_REGS:0,0 GEN_OR_FLOAT_REGS:12000,12000 GEN_OR_VSX_REGS:12000,12000 MEM:0,0 .... (insn 6 3 13 2 (set (reg/v:V2DF 117 [ x ]) (mem:V2DF (plus:DI (reg/v/f:DI 118 [ p ]) (const_int 32 [0x20])) [1 p_2(D)->c+0 S16 A128])) "testsuite/gcc.target/powerpc/dform-3.c":23:8 1148 {vsx_movv2df_64bit} (nil)) (insn 13 6 8 2 (set (reg:V2DF 119 [ x ]) (reg/v:V2DF 117 [ x ])) "testsuite/gcc.target/powerpc/dform-3.c":25:3 -1 (nil)) (insn 8 13 9 2 (parallel [ (set (reg:V2DF 119 [ x ]) (asm_operands:V2DF (" # reg = %0") ("=r") 0 [ (reg:V2DF 119 [ x ]) ] [ (asm_input:V2DF ("0") testsuite/gcc.target/powerpc/dform-3.c:25) ] [] testsuite/gcc.target/powerpc/dform-3.c:25)) (clobber (reg:SI 98 ca)) ]) "testsuite/gcc.target/powerpc/dform-3.c":25:3 -1 --------------- And after my commit, RA take best scenario when preferred reg_class is unkown, which make cost of MEM:0,0 of r117 same as VSX_REGS:0,0, and allocate r117 as VSX_REGS, which create an extra move and failed the testcase.