[PATCH] Make SCCVN constant-fold calls

[Richard Biener]

On Thu, 15 May 2014, Richard Biener wrote:

> 
> For some odd reason I didn't implement this earlier.  This is one
> major source of 2nd-stage opportunities that come up when running
> two adjacent FRE passes.
> 
> Bootstrap and regtest ongoing on x86_64-unknown-linux-gnu.

The following is what I have applied (with also properly
value-numbering VDEFs if there).

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Richard.

2014-05-16  Richard Biener  <rguenther@suse.de>

	* tree-ssa-sccvn.c (visit_use): Also constant-fold calls.

	* gcc.dg/tree-ssa/ssa-fre-41.c: New testcase.

Index: gcc/tree-ssa-sccvn.c
===================================================================
*** gcc/tree-ssa-sccvn.c	(revision 210418)
--- gcc/tree-ssa-sccvn.c	(working copy)
*************** visit_use (tree use)
*** 3566,3593 ****
        else if (is_gimple_call (stmt))
  	{
  	  tree lhs = gimple_call_lhs (stmt);
- 
- 	  /* ???  We could try to simplify calls.  */
- 
  	  if (lhs && TREE_CODE (lhs) == SSA_NAME)
  	    {
! 	      if (stmt_has_constants (stmt))
! 		VN_INFO (lhs)->has_constants = true;
! 	      else
  		{
! 		  /* We reset expr and constantness here because we may
! 		     have been value numbering optimistically, and
! 		     iterating.  They may become non-constant in this case,
! 		     even if they were optimistically constant.  */
! 		  VN_INFO (lhs)->has_constants = false;
! 		  VN_INFO (lhs)->expr = NULL_TREE;
  		}
! 
! 	      if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (lhs))
  		{
! 		  changed = defs_to_varying (stmt);
  		  goto done;
  		}
  	    }
  
  	  if (!gimple_call_internal_p (stmt)
--- 3566,3635 ----
        else if (is_gimple_call (stmt))
  	{
  	  tree lhs = gimple_call_lhs (stmt);
  	  if (lhs && TREE_CODE (lhs) == SSA_NAME)
  	    {
! 	      /* Try constant folding based on our current lattice.  */
! 	      tree simplified = gimple_fold_stmt_to_constant_1 (stmt,
! 								vn_valueize);
! 	      if (simplified)
  		{
! 		  if (dump_file && (dump_flags & TDF_DETAILS))
! 		    {
! 		      fprintf (dump_file, "call ");
! 		      print_gimple_expr (dump_file, stmt, 0, 0);
! 		      fprintf (dump_file, " simplified to ");
! 		      print_generic_expr (dump_file, simplified, 0);
! 		      if (TREE_CODE (lhs) == SSA_NAME)
! 			fprintf (dump_file, " has constants %d\n",
! 				 expr_has_constants (simplified));
! 		      else
! 			fprintf (dump_file, "\n");
! 		    }
  		}
! 	      /* Setting value numbers to constants will occasionally
! 		 screw up phi congruence because constants are not
! 		 uniquely associated with a single ssa name that can be
! 		 looked up.  */
! 	      if (simplified
! 		  && is_gimple_min_invariant (simplified))
  		{
! 		  VN_INFO (lhs)->expr = simplified;
! 		  VN_INFO (lhs)->has_constants = true;
! 		  changed = set_ssa_val_to (lhs, simplified);
! 		  if (gimple_vdef (stmt))
! 		    changed |= set_ssa_val_to (gimple_vdef (stmt),
! 					       gimple_vuse (stmt));
  		  goto done;
  		}
+ 	      else if (simplified
+ 		       && TREE_CODE (simplified) == SSA_NAME)
+ 		{
+ 		  changed = visit_copy (lhs, simplified);
+ 		  if (gimple_vdef (stmt))
+ 		    changed |= set_ssa_val_to (gimple_vdef (stmt),
+ 					       gimple_vuse (stmt));
+ 		  goto done;
+ 		}
+ 	      else
+ 		{
+ 		  if (stmt_has_constants (stmt))
+ 		    VN_INFO (lhs)->has_constants = true;
+ 		  else
+ 		    {
+ 		      /* We reset expr and constantness here because we may
+ 			 have been value numbering optimistically, and
+ 			 iterating.  They may become non-constant in this case,
+ 			 even if they were optimistically constant.  */
+ 		      VN_INFO (lhs)->has_constants = false;
+ 		      VN_INFO (lhs)->expr = NULL_TREE;
+ 		    }
+ 
+ 		  if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (lhs))
+ 		    {
+ 		      changed = defs_to_varying (stmt);
+ 		      goto done;
+ 		    }
+ 		}
  	    }
  
  	  if (!gimple_call_internal_p (stmt)
Index: gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-41.c
===================================================================
*** gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-41.c	(revision 0)
--- gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-41.c	(working copy)
***************
*** 0 ****
--- 1,12 ----
+ /* { dg-do compile } */
+ /* { dg-options "-O -fdump-tree-fre1" } */
+ 
+ int x;
+ int foo (void)
+ {
+   x = 1;
+   return __builtin_ffs (x);
+ }
+ 
+ /* { dg-final { scan-tree-dump-not "ffs" "fre1" } } */
+ /* { dg-final { cleanup-tree-dump "fre1" } } */