https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105123
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:ecc6450668326e52d019b3c298f2c61734ee32c2 commit r11-9755-gecc6450668326e52d019b3c298f2c61734ee32c2 Author: Jakub Jelinek <ja...@redhat.com> Date: Sun Apr 3 21:50:43 2022 +0200 i386: Fix up ix86_expand_vector_init_general [PR105123] The following testcase is miscompiled on ia32. The problem is that at -O0 we end up with: vector(4) short unsigned int _1; short unsigned int u.0_3; ... _1 = {u.0_3, u.0_3, u.0_3, u.0_3}; statement (dead) which is wrongly expanded. elt is (subreg:HI (reg:SI 83 [ u.0_3 ]) 0), tmp_mode SImode, so after convert_mode we start with word (reg:SI 83 [ u.0_3 ]). The intent is to manually broadcast that value to 2 SImode parts, but because we pass word as target to expand_simple_binop, it will overwrite (reg:SI 83 [ u.0_3 ]) and we end up with 0: 10: {r83:SI=r83:SI<<0x10;clobber flags:CC;} 11: {r83:SI=r83:SI|r83:SI;clobber flags:CC;} 12: {r83:SI=r83:SI<<0x10;clobber flags:CC;} 13: {r83:SI=r83:SI|r83:SI;clobber flags:CC;} 14: clobber r110:V4HI 15: r110:V4HI#0=r83:SI 16: r110:V4HI#4=r83:SI as the two ors do nothing and two shifts each by 16 left shift it all away. The following patch fixes that by using NULL_RTX target, so we expand it as 10: {r110:SI=r83:SI<<0x10;clobber flags:CC;} 11: {r111:SI=r110:SI|r83:SI;clobber flags:CC;} 12: {r112:SI=r83:SI<<0x10;clobber flags:CC;} 13: {r113:SI=r112:SI|r83:SI;clobber flags:CC;} 14: clobber r114:V4HI 15: r114:V4HI#0=r111:SI 16: r114:V4HI#4=r113:SI instead. Another possibility would be to pass NULL_RTX only when word == elt and word otherwise, where word would necessarily be a pseudo from the first shift after passing NULL_RTX there once or pass NULL_RTX for the shift and word for ior. 2022-04-03 Jakub Jelinek <ja...@redhat.com> PR target/105123 * config/i386/i386-expand.c (ix86_expand_vector_init_general): Avoid using word as target for expand_simple_binop when doing ASHIFT and IOR. * gcc.target/i386/pr105123.c: New test. (cherry picked from commit e1a74058b784c845e84a0cf1997b54b984df483d)
