http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46883
Ulrich Weigand <uweigand at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |bernds at codesourcery dot | |com, uweigand at gcc dot | |gnu.org --- Comment #3 from Ulrich Weigand <uweigand at gcc dot gnu.org> 2010-12-13 18:54:48 UTC --- Confirmed. A somewhat shorter testcase is: void bar (unsigned char *q, unsigned short *data16s, int len) { int i; for (i = 0; i < len; i++) { q[2 * i] = (((data16s[i] & 0xFF) << 8) | ((data16s[i] >> 8) & 0xFF)) & 0xFF; q[2 * i + 1] = ((unsigned short) (((data16s[i] & 0xFF) << 8) | ((data16s[i] >> 8) & 0xFF))) >> 8; } } The problem seems to be that an insn: (insn 88 86 90 4 (set (reg:SI 240) (zero_extend:SI (subreg:QI (mem:HI (post_inc:SI (reg:SI 220 [ ivtmp.22 ])) [2 MEM[(short unsigned int *)D.2066_62 + 4294967294B]+0 S2 A16]) 0))) a.c:10 152 {*arm_zero_extendqisi2} (expr_list:REG_INC (reg:SI 220 [ ivtmp.22 ]) (nil))) gets transformed by a splitter into: (insn 122 86 90 4 (set (reg:SI 240) (and:SI (subreg:SI (mem:HI (post_inc:SI (reg:SI 220 [ ivtmp.22 ])) [2 MEM[(short unsigned int *)D.2066_62 + 4294967294B]+0 S2 A16]) 0) (const_int 255 [0xff]))) a.c:10 -1 (expr_list:REG_INC (reg:SI 220 [ ivtmp.22 ]) (nil))) But this isn't accepted by the andsi3 pattern, since the (subreg (mem ..)) does not match the s_register_operand predicate. The splitter (define_split [(set (match_operand:SI 0 "register_operand" "") (zero_extend:SI (match_operand:QI 1 "register_operand" "")))] "!arm_arch6" [(set (match_dup 0) (ashift:SI (match_dup 2) (const_int 24))) (set (match_dup 0) (lshiftrt:SI (match_dup 0) (const_int 24)))] { operands[2] = simplify_gen_subreg (SImode, operands[1], QImode, 0); if (TARGET_ARM) { emit_insn (gen_andsi3 (operands[0], operands[2], GEN_INT (255))); DONE; } }) was introduced by Bernd Schmidt's patch to improve zero- and sign-extension handling on ARM (committed 2010-07-02), PR 42172: http://gcc.gnu.org/ml/gcc-patches/2010-06/msg00832.html Bernd, do you have any suggestions how to fix this?