Re: [PATCH] Fix PR56321

[Bill Schmidt <wschmidt at linux dot vnet dot ibm dot com>]

On Mon, 2013-02-18 at 13:05 +0100, Richard Biener wrote:
> 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.

OK, thanks!  Appreciate it.

Bill

> 
> 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);
> >
> >
>