Improve early simplify and match for phiopt

Previously the idea was gimple_simplify_phiopt would call
resimplify with a NULL sequence but that sometimes fails
even if there was only one statement produced. The cases
where it fails is when there are two simplifications happen.
In the case of the min/max production, the first simplifcation
produces:
(convert (min @1 @2))
And then the convert is removed by a second one. The Min statement
will be in the sequence while the op will be a SSA name. This was
rejected before as could not produce something in the sequence.
So this patch changes the way resimplify is called to always passing
a pointer to the sequence and then decide based on if op is a
SSA_NAME or not.

OK? Bootstrapped and tested on x86_64-linux-gnu.

gcc/ChangeLog:

	* tree-ssa-phiopt.c (phiopt_early_allow): Change arguments
	to take sequence and gimple_match_op.  Accept the case where
	op is a SSA_NAME and one statement in the sequence.
	Also allow constants.
	(gimple_simplify_phiopt): Always pass a sequence to resimplify.
	Update call to phiopt_early_allow.  Discard the sequence if not
	used.

gcc/tree-ssa-phiopt.c

@@ -812,11 +812,33 @@ two_value_replacement (basic_block cond_bb, basic_block middle_bb,
   return true;
 }
 
-/* Return TRUE if CODE should be allowed during early phiopt.
-   Currently this is to allow MIN/MAX and ABS/NEGATE.  */
+/* Return TRUE if SEQ/OP pair should be allowed during early phiopt.
+   Currently this is to allow MIN/MAX and ABS/NEGATE and constants.  */
 static bool
-phiopt_early_allow (enum tree_code code)
+phiopt_early_allow (gimple_seq &seq, gimple_match_op &op)
 {
+  /* Don't allow functions. */
+  if (!op.code.is_tree_code ())
+    return false;
+  tree_code code = (tree_code)op.code;
+
+  /* For non-empty sequence, only allow one statement.  */
+  if (!gimple_seq_empty_p (seq))
+    {
+      /* Check to make sure op was already a SSA_NAME.  */
+      if (code != SSA_NAME)
+	return false;
+      if (!gimple_seq_singleton_p (seq))
+	return false;
+      gimple *stmt = gimple_seq_first_stmt (seq);
+      /* Only allow assignments.  */
+      if (!is_gimple_assign (stmt))
+	return false;
+      if (gimple_assign_lhs (stmt) != op.ops[0])
+	return false;
+      code = gimple_assign_rhs_code (stmt);
+    }
+
   switch (code)
     {
       case MIN_EXPR:
@@ -826,6 +848,11 @@ phiopt_early_allow (enum tree_code code)
       case NEGATE_EXPR:
       case SSA_NAME:
 	return true;
+      case INTEGER_CST:
+      case REAL_CST:
+      case VECTOR_CST:
+      case FIXED_CST:
+	return true;
       default:
 	return false;
     }
@@ -844,6 +871,7 @@ gimple_simplify_phiopt (bool early_p, tree type, gimple *comp_stmt,
 			gimple_seq *seq)
 {
   tree result;
+  gimple_seq seq1 = NULL;
   enum tree_code comp_code = gimple_cond_code (comp_stmt);
   location_t loc = gimple_location (comp_stmt);
   tree cmp0 = gimple_cond_lhs (comp_stmt);
@@ -858,18 +886,23 @@ gimple_simplify_phiopt (bool early_p, tree type, gimple *comp_stmt,
   gimple_match_op op (gimple_match_cond::UNCOND,
 		      COND_EXPR, type, cond, arg0, arg1);
 
-  if (op.resimplify (early_p ? NULL : seq, follow_all_ssa_edges))
+  if (op.resimplify (&seq1, follow_all_ssa_edges))
     {
       /* Early we want only to allow some generated tree codes. */
       if (!early_p
-	  || op.code.is_tree_code ()
-	  || phiopt_early_allow ((tree_code)op.code))
+	  || phiopt_early_allow (seq1, op))
 	{
-	  result = maybe_push_res_to_seq (&op, seq);
+	  result = maybe_push_res_to_seq (&op, &seq1);
 	  if (result)
-	    return result;
+	    {
+	      gimple_seq_add_seq_without_update (seq, seq1);
+	      return result;
+	    }
 	}
     }
+  gimple_seq_discard (seq1);
+  seq1 = NULL;
+
   /* Try the inverted comparison, that is !COMP ? ARG1 : ARG0. */
   comp_code = invert_tree_comparison (comp_code, HONOR_NANS (cmp0));
 
@@ -882,18 +915,21 @@ gimple_simplify_phiopt (bool early_p, tree type, gimple *comp_stmt,
   gimple_match_op op1 (gimple_match_cond::UNCOND,
 		       COND_EXPR, type, cond, arg1, arg0);
 
-  if (op1.resimplify (early_p ? NULL : seq, follow_all_ssa_edges))
+  if (op1.resimplify (&seq1, follow_all_ssa_edges))
     {
       /* Early we want only to allow some generated tree codes. */
       if (!early_p
-	  || op1.code.is_tree_code ()
-	  || phiopt_early_allow ((tree_code)op1.code))
+	  || phiopt_early_allow (seq1, op1))
 	{
-	  result = maybe_push_res_to_seq (&op1, seq);
+	  result = maybe_push_res_to_seq (&op1, &seq1);
 	  if (result)
-	    return result;
+	    {
+	      gimple_seq_add_seq_without_update (seq, seq1);
+	      return result;
+	    }
 	}
     }
+  gimple_seq_discard (seq1);
 
   return NULL;
 }