[PATCH] Fix reassociation not to reuse SSA_NAMEs (PR tree-optimization/71631)

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

rewrite_expr_tree tries to reuse SSA_NAMEs if it knows they hold the same
values, which it figures out by setting the changed flag during recursion
if some operand is different.  But in order for this to work reliably,
we need to be started with the right changed value in the outermost call
- we need it to be clear only if the result of rewrite_expr_tree is the
original lhs, i.e. we don't add any further operations afterwards.
This used to be correct before the introduction of negate_result stuff,
i.e. it was clear unless powi_result != NULL.  But negate_result
needs to be treated the same, and we need to be prepared for
rewrite_expr_tree returning in that case something other than lhs.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2016-06-24  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/71631
	* tree-ssa-reassoc.c (reassociate_bb): Pass true as last argument
	to rewrite_expr_tree even if negate_result, move new_lhs var
	declaration and initialization earlier, for powi_result set afterwards
	new_lhs to lhs.  For negate_result, use new_lhs instead of tmp
	if new_lhs != lhs, and don't shadow gsi var.

	* gcc.c-torture/execute/pr71631.c: New test.

--- gcc/tree-ssa-reassoc.c.jj	2016-06-24 12:59:05.632625218 +0200
+++ gcc/tree-ssa-reassoc.c	2016-06-24 17:30:20.493848465 +0200
@@ -5314,6 +5314,7 @@ reassociate_bb (basic_block bb)
 		    }
 		}
 
+	      tree new_lhs = lhs;
 	      /* If the operand vector is now empty, all operands were 
 		 consumed by the __builtin_powi optimization.  */
 	      if (ops.length () == 0)
@@ -5337,7 +5338,6 @@ reassociate_bb (basic_block bb)
 		  machine_mode mode = TYPE_MODE (TREE_TYPE (lhs));
 		  int ops_num = ops.length ();
 		  int width = get_reassociation_width (ops_num, rhs_code, mode);
-		  tree new_lhs = lhs;
 
 		  if (dump_file && (dump_flags & TDF_DETAILS))
 		    fprintf (dump_file,
@@ -5357,7 +5357,8 @@ reassociate_bb (basic_block bb)
                         swap_ops_for_binary_stmt (ops, len - 3, stmt);
 
 		      new_lhs = rewrite_expr_tree (stmt, 0, ops,
-						   powi_result != NULL);
+						   powi_result != NULL
+						   || negate_result);
                     }
 
 		  /* If we combined some repeated factors into a 
@@ -5372,7 +5373,10 @@ reassociate_bb (basic_block bb)
 		      gimple_set_lhs (lhs_stmt, target_ssa);
 		      update_stmt (lhs_stmt);
 		      if (lhs != new_lhs)
-			target_ssa = new_lhs;
+			{
+			  target_ssa = new_lhs;
+			  new_lhs = lhs;
+			}
 		      mul_stmt = gimple_build_assign (lhs, MULT_EXPR,
 						      powi_result, target_ssa);
 		      gimple_set_location (mul_stmt, gimple_location (stmt));
@@ -5386,10 +5390,11 @@ reassociate_bb (basic_block bb)
 		  stmt = SSA_NAME_DEF_STMT (lhs);
 		  tree tmp = make_ssa_name (TREE_TYPE (lhs));
 		  gimple_set_lhs (stmt, tmp);
+		  if (lhs != new_lhs)
+		    tmp = new_lhs;
 		  gassign *neg_stmt = gimple_build_assign (lhs, NEGATE_EXPR,
 							   tmp);
 		  gimple_set_uid (neg_stmt, gimple_uid (stmt));
-		  gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
 		  gsi_insert_after (&gsi, neg_stmt, GSI_NEW_STMT);
 		  update_stmt (stmt);
 		}
--- gcc/testsuite/gcc.c-torture/execute/pr71631.c.jj	2016-06-24 14:58:59.185809799 +0200
+++ gcc/testsuite/gcc.c-torture/execute/pr71631.c	2016-06-24 14:58:59.185809799 +0200
@@ -0,0 +1,32 @@
+/* PR tree-optimization/71631 */
+
+volatile char v;
+int a = 1, b = 1, c = 1;
+
+void
+foo (const char *s)
+{
+  while (*s++)
+    v = *s;
+}
+
+int
+main ()
+{
+  volatile int d = 1;
+  volatile int e = 1;
+  int f = 1 / a;
+  int g = 1U < f;
+  int h = 2 + g;
+  int i = 3 % h;
+  int j = e && b;
+  int k = 1 == c;
+  int l = d != 0;
+  short m = (short) (-1 * i * l);
+  short x = j * (k * m);
+  if (i == 1)
+    foo ("AB");
+  if (x != -1)
+    __builtin_abort ();
+  return 0;
+}

	Jakub