Make fix for PR 83965 handle SLP reduction chains

This patch prevents pattern-matching of fold-left SLP reduction chains,
which the previous patch for 83965 didn't handle properly.  It only
stops the last statement in the group from being matched, but that's
enough to cause the group to be dissolved later.

A better fix would be to put all the information about the reduction
on the the first statement in the reduction chain, so that every
statement in the group can tell what the group is doing.  That doesn't
seem like stage 4 material though.

2018-02-26  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	PR tree-optimization/83965
	* tree-vect-patterns.c (vect_reassociating_reduction_p): Assume
	that grouped statements are part of a reduction chain.  Return
	true if the statement is not marked as a reduction itself but
	is part of a group.
	(vect_recog_dot_prod_pattern): Don't check whether the statement
	is part of a group here.
	(vect_recog_sad_pattern): Likewise.
	(vect_recog_widen_sum_pattern): Likewise.

gcc/testsuite/
	PR tree-optimization/83965
	* gcc.dg/vect/pr83965-2.c: New test.

From-SVN: r257995

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 3e1eae1..6ba082a 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,15 @@
+2018-02-26  Richard Sandiford  <richard.sandiford@linaro.org>
+
+       PR tree-optimization/83965
+       * tree-vect-patterns.c (vect_reassociating_reduction_p): Assume
+       that grouped statements are part of a reduction chain.  Return
+       true if the statement is not marked as a reduction itself but
+       is part of a group.
+       (vect_recog_dot_prod_pattern): Don't check whether the statement
+       is part of a group here.
+       (vect_recog_sad_pattern): Likewise.
+       (vect_recog_widen_sum_pattern): Likewise.
+
 2018-02-26  Eric Botcazou  <ebotcazou@adacore.com>
 
        PR debug/84545

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index a32934b..a927f22 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2018-02-26  Richard Sandiford  <richard.sandiford@linaro.org>
+
+       PR tree-optimization/83965
+       * gcc.dg/vect/pr83965-2.c: New test.
+
 2018-02-26  Tom de Vries  <tom@codesourcery.com>
 
        * gcc.c-torture/compile/regs-arg-size.c (swprintf): Declare.

diff --git a/gcc/testsuite/gcc.dg/vect/pr83965-2.c b/gcc/testsuite/gcc.dg/vect/pr83965-2.c
new file mode 100644 (file)
index 0000000..b9e3260
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr83965-2.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-Ofast -ftrapv" } */
+
+int c;
+unsigned char d;
+int e (unsigned char *f)
+{
+  int g;
+  for (int a; a; a++)
+    {
+      for (int b = 0; b < 6; b++)
+       g += __builtin_abs (f[b] - d);
+      f += c;
+    }
+  return g;
+}

diff --git a/gcc/tree-vect-patterns.c b/gcc/tree-vect-patterns.c
index 34f69e9..621ed07 100644 (file)
--- a/gcc/tree-vect-patterns.c
+++ b/gcc/tree-vect-patterns.c
@@ -222,13 +222,16 @@ vect_recog_temp_ssa_var (tree type, gimple *stmt)
 }
 
 /* Return true if STMT_VINFO describes a reduction for which reassociation
-   is allowed.  */
+   is allowed.  If STMT_INFO is part of a group, assume that it's part of
+   a reduction chain and optimistically assume that all statements
+   except the last allow reassociation.  */
 
 static bool
 vect_reassociating_reduction_p (stmt_vec_info stmt_vinfo)
 {
   return (STMT_VINFO_DEF_TYPE (stmt_vinfo) == vect_reduction_def
-         && STMT_VINFO_REDUC_TYPE (stmt_vinfo) != FOLD_LEFT_REDUCTION);
+         ? STMT_VINFO_REDUC_TYPE (stmt_vinfo) != FOLD_LEFT_REDUCTION
+         : GROUP_FIRST_ELEMENT (stmt_vinfo) != NULL);
 }
 
 /* Function vect_recog_dot_prod_pattern
@@ -350,8 +353,7 @@ vect_recog_dot_prod_pattern (vec<gimple *> *stmts, tree *type_in,
     {
       gimple *def_stmt;
 
-      if (!vect_reassociating_reduction_p (stmt_vinfo)
-         && ! STMT_VINFO_GROUP_FIRST_ELEMENT (stmt_vinfo))
+      if (!vect_reassociating_reduction_p (stmt_vinfo))
        return NULL;
       oprnd0 = gimple_assign_rhs1 (last_stmt);
       oprnd1 = gimple_assign_rhs2 (last_stmt);
@@ -571,8 +573,7 @@ vect_recog_sad_pattern (vec<gimple *> *stmts, tree *type_in,
     {
       gimple *def_stmt;
 
-      if (!vect_reassociating_reduction_p (stmt_vinfo)
-         && ! STMT_VINFO_GROUP_FIRST_ELEMENT (stmt_vinfo))
+      if (!vect_reassociating_reduction_p (stmt_vinfo))
        return NULL;
       plus_oprnd0 = gimple_assign_rhs1 (last_stmt);
       plus_oprnd1 = gimple_assign_rhs2 (last_stmt);
@@ -1256,8 +1257,7 @@ vect_recog_widen_sum_pattern (vec<gimple *> *stmts, tree *type_in,
   if (gimple_assign_rhs_code (last_stmt) != PLUS_EXPR)
     return NULL;
 
-  if (!vect_reassociating_reduction_p (stmt_vinfo)
-      && ! STMT_VINFO_GROUP_FIRST_ELEMENT (stmt_vinfo))
+  if (!vect_reassociating_reduction_p (stmt_vinfo))
     return NULL;
 
   oprnd0 = gimple_assign_rhs1 (last_stmt);