https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104914
--- Comment #8 from YunQiang Su <syq at gcc dot gnu.org> --- (In reply to Andrew Pinski from comment #7) > The initial RTL has a signed extend in there: > > > (insn 20 19 23 2 (set (reg/v:DI 200 [ val+-4 ]) > (sign_extend:DI (subreg:SI (reg/v:DI 200 [ val+-4 ]) 4))) > "/app/example.cpp":7:29 -1 > (nil)) > (jump_insn 23 20 24 2 (set (pc) > (if_then_else (le (subreg/s/u:SI (reg/v:DI 200 [ val+-4 ]) 4) > (const_int 0 [0])) > (label_ref 32) > (pc))) "/app/example.cpp":8:5 -1 > (int_list:REG_BR_PROB 440234148 (nil)) > -> 32) > > > Before combine also looks fine: > (insn 20 19 23 2 (set (reg/v:DI 200 [ val+-4 ]) > (sign_extend:DI (subreg:SI (reg/v:DI 200 [ val+-4 ]) 4))) > "/app/example.cpp":7:29 235 {extendsidi2} > (nil)) Yes. I noticed it. while in mips.md, extendsidi2 is expanded to no instructions at all. ``` ;; Extension insns. ;; Those for integer source operand are ordered widest source type first. ;; When TARGET_64BIT, all SImode integer and accumulator registers ;; should already be in sign-extended form (see TARGET_TRULY_NOOP_TRUNCATION ;; and truncdisi2). We can therefore get rid of register->register ;; instructions if we constrain the source to be in the same register as ;; the destination. ;; ;; Only the pre-reload scheduler sees the type of the register alternatives; ;; we split them into nothing before the post-reload scheduler runs. ;; These alternatives therefore have type "move" in order to reflect ;; what happens if the two pre-reload operands cannot be tied, and are ;; instead allocated two separate GPRs. We don't distinguish between ;; the GPR and LO cases because we don't usually know during pre-reload ;; scheduling whether an operand will be LO or not. (define_insn_and_split "extendsidi2" [(set (match_operand:DI 0 "register_operand" "=d,l,d") (sign_extend:DI (match_operand:SI 1 "nonimmediate_operand" "0,0,m")))] "TARGET_64BIT" "@ # # lw\t%0,%1" "&& reload_completed && register_operand (operands[1], VOIDmode)" [(const_int 0)] { emit_note (NOTE_INSN_DELETED); DONE; } [(set_attr "move_type" "move,move,load") (set_attr "mode" "DI")]) ```