On Tue, Mar 27, 2018 at 11:11 PM, Jakub Jelinek <ja...@redhat.com> wrote:
> Hi!
>
> In 6.x we've changed unsigned if (a < b) a++; into ADD_OVERFLOW ifn,
> which results in different expanded code, which on the following testcase
> unfortunately doesn't combine anymore into the optimal 3 instructions.
>
> The problem is that we want adc[lq] $0, %reg instruction, but simplify-rtx.c
> leaves the apparently useless (plus something const0_rtx) out, just uses
> something, and there is no pattern that matches that.
>
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
> trunk?
>
> 2018-03-27 Jakub Jelinek <ja...@redhat.com>
>
> PR target/85095
> * config/i386/i386.md (*add<mode>3_carry0): New pattern.
>
> * gcc.target/i386/pr85095.c: New test.
>
> --- gcc/config/i386/i386.md.jj 2018-03-27 12:54:54.685244368 +0200
> +++ gcc/config/i386/i386.md 2018-03-27 19:38:43.891451026 +0200
> @@ -6854,6 +6854,23 @@ (define_insn "add<mode>3_carry"
> (set_attr "pent_pair" "pu")
> (set_attr "mode" "<MODE>")])
>
> +(define_insn "*add<mode>3_carry0"
Please name this "*add<mode>3_carry_0". You will also need to
introduce "*addsi3_carry_zext_0". Probably minus patterns have the
same problem, simplify-rtx probably removes (minus ... const_rtx0),
too.
> + [(set (match_operand:SWI 0 "nonimmediate_operand" "=<r>m")
> + (plus:SWI
> + (match_operator:SWI 3 "ix86_carry_flag_operator"
> + [(match_operand 2 "flags_reg_operand") (const_int 0)])
> + (match_operand:SWI 1 "nonimmediate_operand" "0")))
> + (clobber (reg:CC FLAGS_REG))]
> + "ix86_unary_operator_ok (PLUS, <MODE>mode, operands)"
> +{
> + operands[4] = const0_rtx;
> + return "adc{<imodesuffix>}\t{%4, %0|%0, %4}";
Just use "$0" ("0" in intel syntax) in the insn template.
Uros.
