[PATCH] Properly propagate into PHIs in forwprop

[PATCH] Properly propagate into PHIs in forwprop

[Richard Biener]

forwprop has a lattice now (mainly for match-and-simplify simplification)
but it fails to substitute into PHIs or update the lattice for degenerate
PHIs.  Fixed thusly.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

Richard.

2016-08-12  Richard Biener  <rguenther@suse.de>

	* tree-ssa-forwprop.c (pass_forwprop::execute): Propagate
	into PHIs and update the lattice for its def.

Index: gcc/tree-ssa-forwprop.c
===================================================================
--- gcc/tree-ssa-forwprop.c	(revision 239406)
+++ gcc/tree-ssa-forwprop.c	(working copy)
@@ -2107,6 +2107,35 @@ pass_forwprop::execute (function *fun)
       gimple_stmt_iterator gsi;
       basic_block bb = BASIC_BLOCK_FOR_FN (fun, postorder[i]);
 
+      /* Propagate into PHIs and record degenerate ones in the lattice.  */
+      for (gphi_iterator si = gsi_start_phis (bb); !gsi_end_p (si);
+	   gsi_next (&si))
+	{
+	  gphi *phi = si.phi ();
+	  tree res = gimple_phi_result (phi);
+	  if (virtual_operand_p (res))
+	    continue;
+
+	  use_operand_p use_p;
+	  ssa_op_iter it;
+	  tree first = NULL_TREE;
+	  bool all_same = true;
+	  FOR_EACH_PHI_ARG (use_p, phi, it, SSA_OP_USE)
+	    {
+	      tree use = USE_FROM_PTR (use_p);
+	      tree tem = fwprop_ssa_val (use);
+	      if (! first)
+		first = tem;
+	      else if (! operand_equal_p (first, tem, 0))
+		all_same = false;
+	      if (tem != use
+		  && may_propagate_copy (use, tem))
+		propagate_value (use_p, tem);
+	    }
+	  if (all_same)
+	    fwprop_set_lattice_val (res, first);
+	}
+
       /* Apply forward propagation to all stmts in the basic-block.
 	 Note we update GSI within the loop as necessary.  */
       for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); )