Re: [PATCHv2, rs6000] Enable have_cbranchcc4 on rs6000

[David Edelsohn <dje.gcc@gmail.com>]

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On Thu, Nov 17, 2022 at 1:39 AM HAO CHEN GUI <guihaoc@linux.ibm.com> wrote:

> Hi,
>   The patch enables have_cbrnachcc4 which is a flag in ifcvt.cc to
> indicate if branch by CC bits is invalid or not. The new expand pattern
> "cbranchcc4" is created which intend to match the pattern defined in
> "*cbranch", "*cbranch_2insn" and "*creturn". The operand sequence in
> "cbranchcc4" is inline with the definition in gccint. And the operand
> sequence doesn't matter in pattern matching. So I think it should work.
>
>   Compared to last version, one new predicate and one new expander are
> created.
>
>   Bootstrapped and tested on powerpc64-linux BE and LE with no regressions.
> Is this okay for trunk? Any recommendations? Thanks a lot.
>
> ChangeLog
> 2022-11-17  Haochen Gui <guihaoc@linux.ibm.com>
>
> gcc/
>         * config/rs6000/predicates.md (all_branch_comparison_operator):
> New,
>         and includes operators in branch_comparison_operator and
>         extra_insn_branch_comparison_operator.
>         * config/rs6000/rs6000.md (cbranchcc4): New expand pattern.
>
> gcc/testsuite/
>         * gcc.target/powerpc/cbranchcc4.c: New.
>
>
> patch.diff
> diff --git a/gcc/config/rs6000/predicates.md
> b/gcc/config/rs6000/predicates.md
> index b1fcc69bb60..843b6f39b84 100644
> --- a/gcc/config/rs6000/predicates.md
> +++ b/gcc/config/rs6000/predicates.md
> @@ -1308,6 +1308,7 @@ (define_special_predicate "equality_operator"
>
>  ;; Return 1 if OP is a comparison operation that is valid for a branch
>  ;; instruction.  We check the opcode against the mode of the CC value.
> +
>  ;; validate_condition_mode is an assertion.
>  (define_predicate "branch_comparison_operator"
>     (and (match_operand 0 "comparison_operator")
> @@ -1331,6 +1332,11 @@ (define_predicate
> "extra_insn_branch_comparison_operator"
>                                               GET_MODE (XEXP (op, 0))),
>                      1")))
>
> +;; Return 1 if OP is a comparison operation that is valid for a branch.
> +(define_predicate "all_branch_comparison_operator"
> +   (ior (match_operand 0 "branch_comparison_operator")
> +       (match_operand 0 "extra_insn_branch_comparison_operator")))
> +
>  ;; Return 1 if OP is an unsigned comparison operator.
>  (define_predicate "unsigned_comparison_operator"
>    (match_code "ltu,gtu,leu,geu"))
> diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
> index e9e5cd1e54d..7b7d747a85d 100644
> --- a/gcc/config/rs6000/rs6000.md
> +++ b/gcc/config/rs6000/rs6000.md
> @@ -13067,6 +13067,16 @@ (define_insn_and_split "*<code><mode>_cc"
>  ;; Conditional branches.
>  ;; These either are a single bc insn, or a bc around a b.
>
> +(define_expand "cbranchcc4"
> +  [(set (pc)
> +       (if_then_else (match_operator 0 "all_branch_comparison_operator"
> +                       [(match_operand 1 "cc_reg_operand")
> +                        (match_operand 2 "zero_constant")])
> +                     (label_ref (match_operand 3))
> +                     (pc)))]
> +  ""
> +  "")
> +
>

This is better, but the pattern should be near and after the existing
cbranch<mode>4 patterns earlier in the file, not the *cbranch pattern.  It
doesn't match the comment.

Why are you using zero_constant predicate instead of matching (const_int 0)
for operand 2?

Why does this need the new all_branch_comparison_operator?  Can the ifcvt
optimization correctly elide the 2 insn sequence?

Thanks, David


>  (define_insn "*cbranch"
>    [(set (pc)
>         (if_then_else (match_operator 1 "branch_comparison_operator"
> diff --git a/gcc/testsuite/gcc.target/powerpc/cbranchcc4.c
> b/gcc/testsuite/gcc.target/powerpc/cbranchcc4.c
> new file mode 100644
> index 00000000000..528ba1a878d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/cbranchcc4.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-rtl-ce1" } */
> +/* { dg-final { scan-rtl-dump "noce_try_store_flag_constants" "ce1" } } */
> +
> +/* The inner branch should be detected by ifcvt then be converted to a
> setcc
> +   with a plus by noce_try_store_flag_constants.  */
> +
> +int test (unsigned int a, unsigned int b)
> +{
> +    return (a < b ? 0 : (a > b ? 2 : 1));
> +}
>