[3/9] STMT_VINFO_RELATED_STMT handling in vectorizable_store

[Richard Sandiford]

vectorizable_store contains the code:

  for (j = 0; j < ncopies; j++)
    {
      for (i = 0; i < vec_num; i++)
        {
          ...
              if (j == 0)
                STMT_VINFO_VEC_STMT (stmt_info) = *vec_stmt = new_stmt;
              else
                STMT_VINFO_RELATED_STMT (prev_stmt_info) = new_stmt;
              prev_stmt_info = vinfo_for_stmt (new_stmt);
         }
    }

That is, STMT_VINFO_VEC_STMT (stmt_info) and *vec_stmt contain the last
statement emitted for the _last_ vector of the first copy.  However,
for later copies, the last statement for _every_ vector is chained using
STMT_VINFO_RELATED_STMT.  This seems a bit inconsistent, and isn't
what I expected from the comments.  It also seems different from
other vectorisation functions, where each copy has exactly one
STMT_VINFO_RELATED_STMT.  I wasn't sure whether the difference here
was deliberate or not.

The reason I'm changing it is that it makes the control flow for
the new code more obvious.

Tested on x86_64-linux-gnu and arm-linux-gnueabi.  OK to install?

Richard


gcc/
        * tree-vect-stmts.c (vectorizable_store): Only chain one related
        statement per copy.

Index: gcc/tree-vect-stmts.c
===================================================================
--- gcc/tree-vect-stmts.c       2011-04-12 11:55:08.000000000 +0100
+++ gcc/tree-vect-stmts.c       2011-04-12 11:55:09.000000000 +0100
@@ -3612,6 +3612,7 @@ vectorizable_store (gimple stmt, gimple_
 
       if (1)
        {
+         new_stmt = NULL;
          if (strided_store)
            {
              result_chain = VEC_alloc (tree, heap, group_size);
@@ -3669,17 +3670,19 @@ vectorizable_store (gimple stmt, gimple_
              if (slp)
                continue;
 
-             if (j == 0)
-               STMT_VINFO_VEC_STMT (stmt_info) = *vec_stmt =  new_stmt;
-             else
-               STMT_VINFO_RELATED_STMT (prev_stmt_info) = new_stmt;
-
-             prev_stmt_info = vinfo_for_stmt (new_stmt);
              next_stmt = DR_GROUP_NEXT_DR (vinfo_for_stmt (next_stmt));
              if (!next_stmt)
                break;
            }
        }
+      if (!slp)
+       {
+         if (j == 0)
+           STMT_VINFO_VEC_STMT (stmt_info) = *vec_stmt =  new_stmt;
+         else
+           STMT_VINFO_RELATED_STMT (prev_stmt_info) = new_stmt;
+         prev_stmt_info = vinfo_for_stmt (new_stmt);
+       }
     }
 
   VEC_free (tree, heap, dr_chain);