https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106602
--- Comment #14 from Vineet Gupta <vineetg at rivosinc dot com> --- (In reply to Jeffrey A. Law from comment #13) > Trying 7, 8, 9 -> 10: > 7: r140:DI=0x1 > 8: r141:DI=r140:DI<<0x26 > REG_DEAD r140:DI > REG_EQUAL 0x4000000000 > 9: r139:DI=r141:DI-0x40 > REG_DEAD r141:DI > REG_EQUAL 0x3fffffffc0 > 10: r137:DI=r138:DI&r139:DI > REG_DEAD r139:DI > REG_DEAD r138:DI > Failed to match this instruction: > (set (reg:DI 137) > (and:DI (reg:DI 138) > (const_int 274877906880 [0x3fffffffc0]))) > > > That's what we're looking for. I think I had a wrong switch somewhere. > Match that with a define_split and you should be good to go. I think you are missing the original left shift 6. So insn 6 from my dumps is important if we are to match zero_extendsidi2_shifted which matches and+shift (iff 3>>2==0xffffffff). But it feels like you agree on using REG_EQUAL note (if avail) to created merged pattern in try_combine() as opposed to my original thinking of only doing it if regular pattern match failed.