[PATCH] Fix LIM PHI hosting cost

[PATCH] Fix LIM PHI hosting cost

[Richard Biener]

There are two basic errors in the computation - the first is when
min_cost is never adjusted it remains at UINT_MAX (happens when
all PHI arguments are not defined in any loop).  Second is if
the PHI argument is not defined in the same loop as the PHI - then
we accumulate the cost of already invariant stmts (inconsistently
with the LIM cost modelling).

Bootstrap and regtest running on x86_64-unknown-linux-gnu.

Richard.

2014-06-16  Richard Biener  <rguenther@suse.de>

	* tree-ssa-loop-im.c (determine_max_movement): Adjust cost
	of PHI node moving.

	* gcc.dg/tree-ssa/ssa-lim-12.c: New testcase.

Index: gcc/tree-ssa-loop-im.c
===================================================================
*** gcc/tree-ssa-loop-im.c	(revision 211698)
--- gcc/tree-ssa-loop-im.c	(working copy)
*************** determine_max_movement (gimple stmt, boo
*** 729,742 ****
  	    }
  	  if (!add_dependency (val, lim_data, loop, false))
  	    return false;
! 	  def_data = get_lim_data (SSA_NAME_DEF_STMT (val));
! 	  if (def_data)
  	    {
! 	      min_cost = MIN (min_cost, def_data->cost);
! 	      total_cost += def_data->cost;
  	    }
  	}
  
        lim_data->cost += min_cost;
  
        if (gimple_phi_num_args (stmt) > 1)
--- 732,752 ----
  	    }
  	  if (!add_dependency (val, lim_data, loop, false))
  	    return false;
! 
! 	  gimple def_stmt = SSA_NAME_DEF_STMT (val);
! 	  if (gimple_bb (def_stmt)
! 	      && gimple_bb (def_stmt)->loop_father == loop)
  	    {
! 	      def_data = get_lim_data (def_stmt);
! 	      if (def_data)
! 		{
! 		  min_cost = MIN (min_cost, def_data->cost);
! 		  total_cost += def_data->cost;
! 		}
  	    }
  	}
  
+       min_cost = MIN (min_cost, total_cost);
        lim_data->cost += min_cost;
  
        if (gimple_phi_num_args (stmt) > 1)
Index: gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-12.c
===================================================================
*** gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-12.c	(revision 0)
--- gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-12.c	(working copy)
***************
*** 0 ****
--- 1,27 ----
+ /* { dg-do compile } */
+ /* { dg-options "-O -fdump-tree-lim1" } */
+ 
+ int a[1024];
+ 
+ void foo (int x, int z)
+ {
+   int i;
+   int y = -x;
+   for (i = 0; i < 1024; ++i)
+     a[i] = x ? y : z;
+ }
+ 
+ void bar (int x, int z)
+ {
+   int j;
+   for (j = 0; j < 1024; ++j)
+     {
+       int i;
+       int y = -j + z;
+       for (i = 0; i < 1024; ++i)
+ 	a[i] = x ? y : j;
+     }
+ }
+ 
+ /* { dg-final { scan-tree-dump-times "!= 0 ? " 2 "lim1" } } */
+ /* { dg-final { cleanup-tree-dump "lim1" } } */