http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56442
Georg-Johann Lay <gjl at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |wrong-code Status|UNCONFIRMED |NEW Last reconfirmed| |2013-02-25 CC| |gjl at gcc dot gnu.org Component|target |other Ever Confirmed|0 |1 Severity|major |normal --- Comment #2 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2013-02-25 10:56:02 UTC --- Enabling others to understand this... In .reload dump, we have correct code: (insn 418 417 113 3 (set (reg:HI 24 r24) (const:HI (plus:HI (symbol_ref:HI ("array") [flags 0x2] <var_decl 0x1e405a0 array>) (const_int 4 [0x4])))) 32 {*movhi} (nil)) (insn 113 418 114 3 (set (reg:HI 14 r14 [94]) (minus:HI (reg:HI 14 r14 [94]) (reg:HI 24 r24))) 65 {subhi3} (nil)) (insn 114 113 115 3 (set (reg:HI 14 r14 [94]) (lshiftrt:HI (reg:HI 14 r14 [94]) (const_int 2 [0x2]))) 217 {lshrhi3} (nil)) (insn 115 114 118 3 (parallel [ (set (reg:HI 14 r14 [94]) (and:HI (reg:HI 14 r14 [94]) (const_int 3 [0x3]))) (clobber (reg:QI 25 r25)) ]) 175 {andhi3} (nil)) (insn 118 115 119 3 (set (reg:SF 18 r18 [orig:65 D.1335 ] [65]) (mem:SF (symbol_ref:HI ("array") [flags 0x2] <var_decl 0x1e405a0 array>) [2 MEM[base: D.1358_18, offset: 0B]+0 S4 A8])) foo.c:15 37 {*movsf} (nil)) (insn 119 118 122 3 (set (reg:HI 28 r28 [orig:96 ivtmp.10 ] [96]) (const:HI (plus:HI (symbol_ref:HI ("array") [flags 0x2] <var_decl 0x1e405a0 array>) (const_int 4 [0x4])))) 32 {*movhi} (expr_list:REG_EQUAL (const:HI (plus:HI (symbol_ref:HI ("array") [flags 0x2] <var_decl 0x1e405a0 array>) (const_int 4 [0x4]))) (nil))) This is changed by .postreload to: (insn 119 118 122 3 (set (reg:HI 28 r28 [orig:96 ivtmp.10 ] [96]) (reg:HI 24 r24)) 32 {*movhi} (expr_list:REG_EQUAL (const:HI (plus:HI (symbol_ref:HI ("array") [flags 0x2] <var_decl 0x1e405a0 array>) (const_int 4 [0x4]))) (nil))) This is wrong because reg:HI 24 is (partly) clobbered by insn 115 and thus reg:HI 24 must not be used past insn 115. Component is not target, the target description of andhi3 insn is all right. According to S, the bad transformation happens in: postreload.c:reload_cse_move2add()