Re: [PATCH] aarch64/expr: Use ccmp when the outer expression is used twice [PR100942]

[Andrew Pinski <pinskia@gmail.com>]

On Tue, Dec 12, 2023 at 12:22 AM Andrew Pinski <quic_apinski@quicinc.com> wrote:
>
> Ccmp is not used if the result of the and/ior is used by both
> a GIMPLE_COND and a GIMPLE_ASSIGN. This improves the code generation
> here by using ccmp in this case.
> Two changes is required, first we need to allow the outer statement's
> result be used more than once.
> The second change is that during the expansion of the gimple, we need
> to try using ccmp. This is needed because we don't use expand the ssa
> name of the lhs but rather expand directly from the gimple.
>
> A small note on the ccmp_4.c testcase, we should be able to get slightly
> better than with this patch but it is one extra instruction compared to
> before.
>
> Bootstraped and tested on aarch64-linux-gnu with no regressions.

Ping?

>
>         PR target/100942
>
> gcc/ChangeLog:
>
>         * ccmp.cc (ccmp_candidate_p): Add outer argument.
>         Allow if the outer is true and the lhs is used more
>         than once.
>         (expand_ccmp_expr): Update call to ccmp_candidate_p.
>         * cfgexpand.cc (expand_gimple_stmt_1): Try using ccmp
>         for binary assignments.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.target/aarch64/ccmp_3.c: New test.
>         * gcc.target/aarch64/ccmp_4.c: New test.
>
> Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
> ---
>  gcc/ccmp.cc                               |  9 +++---
>  gcc/cfgexpand.cc                          | 25 ++++++++++++++++
>  gcc/testsuite/gcc.target/aarch64/ccmp_3.c | 20 +++++++++++++
>  gcc/testsuite/gcc.target/aarch64/ccmp_4.c | 35 +++++++++++++++++++++++
>  4 files changed, 85 insertions(+), 4 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/aarch64/ccmp_3.c
>  create mode 100644 gcc/testsuite/gcc.target/aarch64/ccmp_4.c
>
> diff --git a/gcc/ccmp.cc b/gcc/ccmp.cc
> index 1bd6fadea35..a274f8c3d53 100644
> --- a/gcc/ccmp.cc
> +++ b/gcc/ccmp.cc
> @@ -92,7 +92,7 @@ ccmp_tree_comparison_p (tree t, basic_block bb)
>
>  /* Check whether G is a potential conditional compare candidate.  */
>  static bool
> -ccmp_candidate_p (gimple *g)
> +ccmp_candidate_p (gimple *g, bool outer = false)
>  {
>    tree lhs, op0, op1;
>    gimple *gs0, *gs1;
> @@ -109,8 +109,9 @@ ccmp_candidate_p (gimple *g)
>    lhs = gimple_assign_lhs (g);
>    op0 = gimple_assign_rhs1 (g);
>    op1 = gimple_assign_rhs2 (g);
> -  if ((TREE_CODE (op0) != SSA_NAME) || (TREE_CODE (op1) != SSA_NAME)
> -      || !has_single_use (lhs))
> +  if ((TREE_CODE (op0) != SSA_NAME) || (TREE_CODE (op1) != SSA_NAME))
> +    return false;
> +  if (!outer && !has_single_use (lhs))
>      return false;
>
>    bb = gimple_bb (g);
> @@ -284,7 +285,7 @@ expand_ccmp_expr (gimple *g, machine_mode mode)
>    rtx_insn *last;
>    rtx tmp;
>
> -  if (!ccmp_candidate_p (g))
> +  if (!ccmp_candidate_p (g, true))
>      return NULL_RTX;
>
>    last = get_last_insn ();
> diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc
> index b860be8bb77..0f9aad8e3eb 100644
> --- a/gcc/cfgexpand.cc
> +++ b/gcc/cfgexpand.cc
> @@ -74,6 +74,7 @@ along with GCC; see the file COPYING3.  If not see
>  #include "output.h"
>  #include "builtins.h"
>  #include "opts.h"
> +#include "ccmp.h"
>
>  /* Some systems use __main in a way incompatible with its use in gcc, in these
>     cases use the macros NAME__MAIN to give a quoted symbol and SYMBOL__MAIN to
> @@ -3972,6 +3973,30 @@ expand_gimple_stmt_1 (gimple *stmt)
>             if (GET_CODE (target) == SUBREG && SUBREG_PROMOTED_VAR_P (target))
>               promoted = true;
>
> +           /* Try to expand conditonal compare.  */
> +           if (targetm.gen_ccmp_first
> +               && gimple_assign_rhs_class (assign_stmt) == GIMPLE_BINARY_RHS)
> +             {
> +               machine_mode mode = TYPE_MODE (TREE_TYPE (lhs));
> +               gcc_checking_assert (targetm.gen_ccmp_next != NULL);
> +               temp = expand_ccmp_expr (stmt, mode);
> +               if (temp)
> +                 {
> +                   if (promoted)
> +                     {
> +                       int unsignedp = SUBREG_PROMOTED_SIGN (target);
> +                       convert_move (SUBREG_REG (target), temp, unsignedp);
> +                     }
> +                   else
> +                    {
> +                       temp = force_operand (temp, target);
> +                       if (temp != target)
> +                         emit_move_insn (target, temp);
> +                     }
> +                   return;
> +                 }
> +             }
> +
>             ops.code = gimple_assign_rhs_code (assign_stmt);
>             ops.type = TREE_TYPE (lhs);
>             switch (get_gimple_rhs_class (ops.code))
> diff --git a/gcc/testsuite/gcc.target/aarch64/ccmp_3.c b/gcc/testsuite/gcc.target/aarch64/ccmp_3.c
> new file mode 100644
> index 00000000000..a2b47fbee14
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/ccmp_3.c
> @@ -0,0 +1,20 @@
> +/* { dg-options "-O2" } */
> +/* PR target/100942 */
> +
> +void foo(void);
> +int f1(int a, int b)
> +{
> +  int c = a == 0 || b == 0;
> +  if (c) foo();
> +  return c;
> +}
> +
> +/* We should get one cmp followed by ccmp and one cset. */
> +/* { dg-final { scan-assembler "\tccmp\t" } } */
> +/* { dg-final { scan-assembler-times "\tcset\t" 1 } } */
> +/* { dg-final { scan-assembler-times "\tcmp\t" 1 } } */
> +/* And not get 2 cmps and 2 (or more cset) and orr and a cbnz. */
> +/* { dg-final { scan-assembler-not "\torr\t" } } */
> +/* { dg-final { scan-assembler-not "\tcbnz\t" } } */
> +/* { dg-final { scan-assembler-not "\tcbz\t" } } */
> +
> diff --git a/gcc/testsuite/gcc.target/aarch64/ccmp_4.c b/gcc/testsuite/gcc.target/aarch64/ccmp_4.c
> new file mode 100644
> index 00000000000..bc0f57a7c59
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/ccmp_4.c
> @@ -0,0 +1,35 @@
> +/* { dg-options "-O2" } */
> +/* PR target/100942 */
> +
> +void foo(void);
> +int f1(int a, int b, int d)
> +{
> +  int c = a < 8 || b < 9;
> +  int e = d < 11 || c;
> +  if (e) foo();
> +  return c;
> +}
> +
> +/*
> +  We really should get:
> +        cmp     w0, 7
> +        ccmp    w1, 8, 4, gt
> +        cset    w0, le
> +        ccmp    w2, 10, 4, gt
> +        ble     .L11
> +
> +  But we currently get:
> +        cmp     w0, 7
> +        ccmp    w1, 8, 4, gt
> +        cset    w0, le
> +        cmp     w0, 0
> +        ccmp    w2, 10, 4, eq
> +        ble     .L11
> +  The middle cmp is not needed.
> + */
> +
> +/* We should end up with only one cmp and 2 ccmp and 1 cset but currently we get 2 cmp
> +   though. */
> +/* { dg-final { scan-assembler-times "\tccmp\t" 2 } } */
> +/* { dg-final { scan-assembler-times "\tcset\t" 1 } } */
> +/* { dg-final { scan-assembler-times "\tcmp\t" 1 { xfail *-*-* } } } */
> --
> 2.39.3
>