http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50603
--- Comment #4 from H.J. Lu <hjl.tools at gmail dot com> 2011-10-06 19:19:23 UTC --- Combine failed: (set (mem:SI (and:DI (plus:DI (subreg:DI (mult:SI (reg/v:SI 84 [ i ]) (const_int 4 [0x4])) 0) (subreg:DI (reg:SI 106) 0)) (const_int 4294967292 [0xfffffffc])) [3 MEM[symbol: x, index: D.2741_12, step: 4, offset: 4294967292B]+0 S4 A32]) (reg/v:SI 84 [ i ])) for (insn 37 35 39 3 (set (reg:SI 90) (plus:SI (mult:SI (reg/v:SI 84 [ i ]) (const_int 4 [0x4])) (reg:SI 106))) x.i:11 247 {*leasi_2} (nil)) (insn 39 37 41 3 (set (mem:SI (zero_extend:DI (reg:SI 90)) [3 MEM[symbol: x, index: D.2741_12, step: 4, offset: 4294967292B]+0 S4 A32]) (reg/v:SI 84 [ i ])) x.i:11 64 {*movsi_internal} (expr_list:REG_DEAD (reg:SI 90) (nil))) Since address is 32bit aligned, 0xfffffffc is the same as 0xffffffff. But we don't have this information.