https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107404
rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |sayle at gcc dot gnu.org, | |uros at gcc dot gnu.org Status|ASSIGNED |NEW Assignee|rsandifo at gcc dot gnu.org |unassigned at gcc dot gnu.org --- Comment #3 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> --- This is due to the peephole2 added in r12-2640-gf7bf03cf69cc: ;; Eliminate a reg-reg mov by inverting the condition of a cmov (#2). ;; mov r2,r3; mov r0,r1; dec r0; cmov r0,r2 -> dec r1; mov r0,r3; cmov r0, r1 (define_peephole2 [(set (match_operand:SWI248 2 "general_reg_operand") (match_operand:SWI248 3 "general_gr_operand")) (set (match_operand:SWI248 0 "general_reg_operand") (match_operand:SWI248 1 "general_reg_operand")) (parallel [(set (reg FLAGS_REG) (match_operand 5)) (set (match_dup 0) (match_operand:SWI248 6))]) (set (match_dup 0) (if_then_else:SWI248 (match_operator 4 "ix86_comparison_operator" [(reg FLAGS_REG) (const_int 0)]) (match_dup 0) (match_dup 2)))] "TARGET_CMOVE && REGNO (operands[2]) != REGNO (operands[0]) && REGNO (operands[2]) != REGNO (operands[1]) && peep2_reg_dead_p (2, operands[1]) && peep2_reg_dead_p (4, operands[2]) && !reg_overlap_mentioned_p (operands[0], operands[3])" [(parallel [(set (match_dup 7) (match_dup 8)) (set (match_dup 1) (match_dup 9))]) (set (match_dup 0) (match_dup 3)) (set (match_dup 0) (if_then_else:SWI248 (match_dup 4) (match_dup 1) (match_dup 0)))] { operands[7] = SET_DEST (XVECEXP (PATTERN (peep2_next_insn (2)), 0, 0)); operands[8] = replace_rtx (operands[5], operands[0], operands[1], true); operands[9] = replace_rtx (operands[6], operands[0], operands[1], true); }) The conditions make sure that the 2<-3 and 0<-1 moves are independent, but they don't check what effect the 2<-3 move has on the third instruction. I don't know if the intention was to exclude cases where operands 5 and 6 reference operand 2, or whether the intention was to cope with those cases where possible.