Avoid matching the same pattern statement twice

r262275 allowed pattern matching on pattern statements.  Testing for
SVE on more benchmarks showed a case where this interacted badly
with 14/n.

The new over-widening detection could narrow a COND_EXPR A to another
COND_EXPR B, which mixed_size_cond could then match.  This was working
as expected.  However, we left B (now dead) in the pattern definition
sequence with a non-null PATTERN_DEF_SEQ.  mask_conversion also
matched B, and unlike most recognisers, didn't clear PATTERN_DEF_SEQ
before adding statements to it.  This meant that the statements
created by mixed_size_cond appeared in two supposedy separate
sequences, causing much confusion.

This patch removes pattern statements that are replaced by further
pattern statements.  As a belt-and-braces fix, it also nullifies
PATTERN_DEF_SEQ on failure, in the same way Richard B. did recently
for RELATED_STMT.

I have patches to clean up the PATTERN_DEF_SEQ handling, but they
only apply after the complete PR85694 sequence, whereas this needs
to go in before 14/n.

Tested on aarch64-linux-gnu, arm-linux-gnueabihf and x86_64-linux-gnu.
OK to install?

Richard


2018-07-03  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-patterns.c (vect_mark_pattern_stmts): Remove pattern
	statements that have been replaced by further pattern statements.
	(vect_pattern_recog_1): Clear STMT_VINFO_PATTERN_DEF_SEQ on failure.

gcc/testsuite/
	* gcc.dg/vect/vect-mixed-size-cond-1.c: New test.

On Tue, Jul 3, 2018 at 10:02 AM Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> r262275 allowed pattern matching on pattern statements.  Testing for
> SVE on more benchmarks showed a case where this interacted badly
> with 14/n.
>
> The new over-widening detection could narrow a COND_EXPR A to another
> COND_EXPR B, which mixed_size_cond could then match.  This was working
> as expected.  However, we left B (now dead) in the pattern definition
> sequence with a non-null PATTERN_DEF_SEQ.  mask_conversion also
> matched B, and unlike most recognisers, didn't clear PATTERN_DEF_SEQ
> before adding statements to it.  This meant that the statements
> created by mixed_size_cond appeared in two supposedy separate
> sequences, causing much confusion.
>
> This patch removes pattern statements that are replaced by further
> pattern statements.  As a belt-and-braces fix, it also nullifies
> PATTERN_DEF_SEQ on failure, in the same way Richard B. did recently
> for RELATED_STMT.
>
> I have patches to clean up the PATTERN_DEF_SEQ handling, but they
> only apply after the complete PR85694 sequence, whereas this needs
> to go in before 14/n.
>
> Tested on aarch64-linux-gnu, arm-linux-gnueabihf and x86_64-linux-gnu.
> OK to install?

OK.

Richard.

> Richard
>
>
> 2018-07-03  Richard Sandiford  <richard.sandiford@arm.com>
>
> gcc/
>         * tree-vect-patterns.c (vect_mark_pattern_stmts): Remove pattern
>         statements that have been replaced by further pattern statements.
>         (vect_pattern_recog_1): Clear STMT_VINFO_PATTERN_DEF_SEQ on failure.
>
> gcc/testsuite/
>         * gcc.dg/vect/vect-mixed-size-cond-1.c: New test.
>
> Index: gcc/tree-vect-patterns.c
> ===================================================================
> --- gcc/tree-vect-patterns.c    2018-07-02 14:34:45.857732632 +0100
> +++ gcc/tree-vect-patterns.c    2018-07-03 08:56:56.610251460 +0100
> @@ -4295,6 +4295,9 @@ vect_mark_pattern_stmts (gimple *orig_st
>        gimple_stmt_iterator gsi = gsi_for_stmt (orig_stmt, orig_def_seq);
>        gsi_insert_seq_before_without_update (&gsi, def_seq, GSI_SAME_STMT);
>        gsi_insert_before_without_update (&gsi, pattern_stmt, GSI_SAME_STMT);
> +
> +      /* Remove the pattern statement that this new pattern replaces.  */
> +      gsi_remove (&gsi, false);
>      }
>    else
>      vect_set_pattern_stmt (pattern_stmt, orig_stmt_info, pattern_vectype);
> @@ -4358,6 +4361,8 @@ vect_pattern_recog_1 (vect_recog_func *r
>           if (!is_pattern_stmt_p (stmt_info))
>             STMT_VINFO_RELATED_STMT (stmt_info) = NULL;
>         }
> +      /* Clear any half-formed pattern definition sequence.  */
> +      STMT_VINFO_PATTERN_DEF_SEQ (stmt_info) = NULL;
>        return;
>      }
>
> Index: gcc/testsuite/gcc.dg/vect/vect-mixed-size-cond-1.c
> ===================================================================
> --- /dev/null   2018-06-13 14:36:57.192460992 +0100
> +++ gcc/testsuite/gcc.dg/vect/vect-mixed-size-cond-1.c  2018-07-03 08:56:56.610251460 +0100
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +
> +int
> +f (unsigned char *restrict x, short *restrict y)
> +{
> +  for (int i = 0; i < 100; ++i)
> +    {
> +      unsigned short a = (x[i] + 11) >> 1;
> +      unsigned short b = (x[i] + 42) >> 2;
> +      unsigned short cmp = y[i] == 0 ? a : b;
> +      int res = cmp + 1;
> +      x[i] = res;
> +    }
> +}