Re: [PATCH] Fix PR56321

[Richard Biener <richard dot guenther at gmail dot com>]

On Fri, Feb 15, 2013 at 6:53 PM, Bill Schmidt
<wschmidt@linux.vnet.ibm.com> wrote:
> When we remove __builtin_pow statements as part of reassociation, we
> have to unlink the associated VDEF.  We've always done this when we
> directly remove the statement.  However, in reassociation the statements
> are sometimes modified in place instead of removed, potentially leaving
> one or more dangling VUSEs.  This patch solves the problem by unlinking
> the VDEF when the statement's operands are added to the ops list.
>
> Bootstrapped and regression tested on powerpc64-unknown-linux-gnu with
> no new regressions.  The new test case is the code that exposed the
> problem in PR56321.  Ok for trunk?

No, that's way to complicated.  The issue is that

static void
propagate_op_to_single_use (tree op, gimple stmt, tree *def)
{
...
  gsi = gsi_for_stmt (stmt);
  gsi_remove (&gsi, true);
  release_defs (stmt);

  if (is_gimple_call (stmt))
    unlink_stmt_vdef (stmt);

tries to unlink the stmts VDEF after releasing it.  That doesn't work.

A proper fix is

Index: tree-ssa-reassoc.c
===================================================================
--- tree-ssa-reassoc.c  (revision 196115)
+++ tree-ssa-reassoc.c  (working copy)
@@ -1062,11 +1062,9 @@ propagate_op_to_single_use (tree op, gim
   if (TREE_CODE (op) != SSA_NAME)
     update_stmt (use_stmt);
   gsi = gsi_for_stmt (stmt);
+  unlink_stmt_vdef (stmt);
   gsi_remove (&gsi, true);
   release_defs (stmt);
-
-  if (is_gimple_call (stmt))
-    unlink_stmt_vdef (stmt);
 }

 /* Walks the linear chain with result *DEF searching for an operation

I'll take care of it in a second.

Thanks,
Richard.


> Thanks,
> Bill
>
>
> Index: gcc/testsuite/gcc.dg/tree-ssa/pr56321.c
> ===================================================================
> --- gcc/testsuite/gcc.dg/tree-ssa/pr56321.c     (revision 0)
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr56321.c     (revision 0)
> @@ -0,0 +1,12 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -ffast-math -fdump-tree-optimized" } */
> +
> +float foo(int n)
> +{
> +  return ((2.0*n*n)/3.0+2.0*n);
> +}
> +
> +/* { dg-final { scan-tree-dump-times "__builtin_pow" 0 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " \\* " 2 "optimized" } } */
> +/* { dg-final { scan-tree-dump-times " \\+ " 1 "optimized" } } */
> +/* { dg-final { cleanup-tree-dump "optimized" } } */
> Index: gcc/tree-ssa-reassoc.c
> ===================================================================
> --- gcc/tree-ssa-reassoc.c      (revision 196053)
> +++ gcc/tree-ssa-reassoc.c      (working copy)
> @@ -3386,6 +3386,10 @@ linearize_expr_tree (vec<operand_entry_t> *ops, gi
>             {
>               add_repeat_to_ops_vec (ops, base, exponent);
>               gimple_set_visited (binrhsdef, true);
> +             // We may not physically remove the call later because
> +             // stmts are preferably modified in place.  But we have
> +             // to remove any VDEF associated with the call regardless.
> +             unlink_stmt_vdef (binrhsdef);
>             }
>           else
>             add_to_ops_vec (ops, binrhs);
> @@ -3396,6 +3400,10 @@ linearize_expr_tree (vec<operand_entry_t> *ops, gi
>             {
>               add_repeat_to_ops_vec (ops, base, exponent);
>               gimple_set_visited (binlhsdef, true);
> +             // We may not physically remove the call later because
> +             // stmts are preferably modified in place.  But we have
> +             // to remove any VDEF associated with the call regardless.
> +             unlink_stmt_vdef (binlhsdef);
>             }
>           else
>             add_to_ops_vec (ops, binlhs);
> @@ -3445,6 +3453,10 @@ linearize_expr_tree (vec<operand_entry_t> *ops, gi
>      {
>        add_repeat_to_ops_vec (ops, base, exponent);
>        gimple_set_visited (SSA_NAME_DEF_STMT (binrhs), true);
> +      // We may not physically remove the call later because
> +      // stmts are preferably modified in place.  But we have
> +      // to remove any VDEF associated with the call regardless.
> +      unlink_stmt_vdef (SSA_NAME_DEF_STMT (binrhs));
>      }
>    else
>      add_to_ops_vec (ops, binrhs);
>
>