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Compare Elimination problems



For a 16 bit CPU the cmpelim pass is changing

(insn 33 84 85 6 (parallel [
            (set (reg:HI 1 r1)
                (ashift:HI (reg:HI 1 r1)
                    (const_int 1 [0x1])))
            (clobber (reg:CC_NOOV 7 flags))
]) ../gcc/testsuite/gcc.c-torture/execute/960311-3.c:18 33 {ashlhi3}

(insn 34 87 35 6 (set (reg:CC_NOOV 7 flags)
        (compare:CC_NOOV (reg:SI 0 r0)
(const_int 0 [0]))) ../gcc/testsuite/gcc.c-torture/execute/960311-3.c:20 39 {*comparesi3_nov}

(jump_insn 35 34 36 6 (set (pc)
        (if_then_else (ge (reg:CC_NOOV 7 flags)

to

(insn 33 84 85 6 (parallel [
            (set (reg:HI 1 r1)
                (ashift:HI (reg:HI 1 r1)
                    (const_int 1 [0x1])))
            (set (reg:CC_NOOV 7 flags)
                (compare:CC_NOOV (ashift:HI (reg:HI 1 r1)
                        (const_int 1 [0x1]))
                    (const_int 0 [0])))
]) ../gcc/testsuite/gcc.c-torture/execute/960311-3.c:18 29 {ashlhi3_cc}

(jump_insn 35 87 36 6 (set (pc)
        (if_then_else (ge (reg:CC_NOOV 7 flags)


(reg:HI r1) is a subreg of (reg:SI r0) however the cmpelim seems to be substituting the compare of (reg:HI r1 and 0) for the compare of (reg:SI r0 and 0) ?

While I'm here, in i386.md some of the flag setting operations specify a mode and some don't . Eg

(define_expand "cmp<mode>_1"
  [(set (reg:CC FLAGS_REG)
    (compare:CC (match_operand:SWI48 0 "nonimmediate_operand")


(define_insn "*add<mode>_3"
  [(set (reg FLAGS_REG)
    (compare

Can anyone explain the significance of this ?

Thanks, Paul.






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