[PATCH] Improve PHI-OPT when there are multiple phis

[Andrew Pinski]

Hi,
  Right now PHI-OPT does try to handle the case where we have multiple
PHIs but the other PHIs have the same value for the edges we care
about.
This fixes the issue and allows PHI-OPT to handle a few more cases and
it removes the TODO in the comments.

OK For 4.8? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

Thanks,
Andrew Pinski

ChangeLog:
* tree-ssa-phiopt.c (gimple_phi_singleton_for_edges): New function.
(tree_ssa_phiopt_worker): Use gimple_phi_singleton_for_edges.
(empty_block_p): Check also if the PHIs for the block are empty.

testsuite/ChangeLog:
* gcc.dg/tree-ssa/phi-opt-7.c: New testcase.
-------------- next part --------------
Index: testsuite/gcc.dg/tree-ssa/phi-opt-7.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/phi-opt-7.c	(revision 0)
+++ testsuite/gcc.dg/tree-ssa/phi-opt-7.c	(revision 0)
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-tree-optimized" } */
+
+int g(int,int);
+int f(int t, int c)
+{
+  int d = 0;
+  int e = 0;
+  if (t)
+    {
+      d = t;
+      if (c) e = 1;
+    }
+  else d = 0, e = 0;
+  return g(d,e);
+}
+
+/* There should be one ifs as one of them should be changed into
+   a conditional and the other should be there still.  */
+/* { dg-final { scan-tree-dump-times "if" 1 "optimized" }  }*/
+/* { dg-final { scan-tree-dump-times "D.\[0-9\]*_\[0-9\]* = c_\[0-9\]*.D. != 0" 1 "optimized"  } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
+
Index: tree-ssa-phiopt.c
===================================================================
--- tree-ssa-phiopt.c	(revision 183458)
+++ tree-ssa-phiopt.c	(working copy)
@@ -192,6 +192,33 @@ tree_ssa_cs_elim (void)
   return tree_ssa_phiopt_worker (true);
 }
 
+/* Return the singleton PHI in the SEQ of PHIs for edges E0 and E1. */
+
+static gimple
+gimple_phi_singleton_for_edges (gimple_seq seq, edge e0, edge e1)
+{
+  gimple_stmt_iterator i;
+  gimple phi = NULL;
+  if (gimple_seq_singleton_p (seq))
+    return gsi_stmt (gsi_start (seq));
+  for (i = gsi_start (seq); !gsi_end_p (i); gsi_next (&i))
+    {
+      gimple p = gsi_stmt (i);
+      /* If the PHI arguments are equal then we can skip this PHI. */
+      if (operand_equal_for_phi_arg_p (gimple_phi_arg_def (p, e0->dest_idx),
+				       gimple_phi_arg_def (p, e1->dest_idx)))
+	continue;
+
+      /* If we already have a PHI that has the two edge arguments are
+	 different, then return it is not a singleton for these PHIs. */
+      if (phi)
+	return NULL;
+
+      phi = p;
+    }
+  return phi;
+}
+
 /* For conditional store replacement we need a temporary to
    put the old contents of the memory in.  */
 static tree condstoretemp;
@@ -313,23 +340,9 @@ tree_ssa_phiopt_worker (bool do_store_el
       else
 	{
 	  gimple_seq phis = phi_nodes (bb2);
-	  gimple_stmt_iterator gsi;
+	  phi = gimple_phi_singleton_for_edges (phis, e1, e2);
 
-	  /* Check to make sure that there is only one non-virtual PHI node.
-	     TODO: we could do it with more than one iff the other PHI nodes
-	     have the same elements for these two edges.  */
-	  phi = NULL;
-	  for (gsi = gsi_start (phis); !gsi_end_p (gsi); gsi_next (&gsi))
-	    {
-	      if (!is_gimple_reg (gimple_phi_result (gsi_stmt (gsi))))
-		continue;
-	      if (phi)
-		{
-		  phi = NULL;
-		  break;
-		}
-	      phi = gsi_stmt (gsi);
-	    }
+	  /* Check to make sure that there is only one PHI node. */
 	  if (!phi)
 	    continue;
 
@@ -431,6 +444,8 @@ empty_block_p (basic_block bb)
 {
   /* BB must have no executable statements.  */
   gimple_stmt_iterator gsi = gsi_after_labels (bb);
+  if (phi_nodes (bb))
+    return false;
   if (gsi_end_p (gsi))
     return true;
   if (is_gimple_debug (gsi_stmt (gsi)))