Hi!
On the following testcase, there is a redundant & 1 and when reassociating,
we remove the redundant & 1. The outer 2 ops are the same, so changed
is still false when we reach rewrite_expr_tree with the last 2 ops (i.e.
last statement). But, as we don't keep that statement as is nor just swap
the arguments, that isn't a guarantee that the SSA_NAME has always the same
value as previously (in this case we've dropped the & 1 there), so the
following patch ensures we don't reuse the SSA_NAME unless:
1) we don't change the stmt at all
2) we just swap the two arguments
3) opindex == 0 (reassociate_bb doesn't really expect to see a new SSA_NAME
if it hasn't called it with changed = true, and in that case the SSA_NAME
is necessarily always the same as before the optimization, otherwise
the optimization would be wrong.
This way, we don't preserve bogus VR info, nor generate incorrect debug
info.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2015-02-26 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/65216
* tree-ssa-reassoc.c (rewrite_expr_tree): Force creation of
new stmt and new SSA_NAME for lhs whenever the arguments have
changed and weren't just swapped. Fix comment typo.
* gcc.c-torture/execute/pr65216.c: New test.
--- gcc/tree-ssa-reassoc.c.jj 2015-02-14 09:21:56.000000000 +0100
+++ gcc/tree-ssa-reassoc.c 2015-02-26 13:03:24.308614169 +0100
@@ -3532,7 +3532,7 @@ rewrite_expr_tree (gimple stmt, unsigned
/* The final recursion case for this function is that you have
exactly two operations left.
- If we had one exactly one op in the entire list to start with, we
+ If we had exactly one op in the entire list to start with, we
would have never called this function, and the tail recursion
rewrites them one at a time. */
if (opindex + 2 == ops.length ())
@@ -3553,7 +3553,11 @@ rewrite_expr_tree (gimple stmt, unsigned
print_gimple_stmt (dump_file, stmt, 0, 0);
}
- if (changed)
+ /* Even when changed is false, reassociation could have e.g. removed
+ some redundant operations, so unless we are just swapping the
+ arguments or unless there is no change at all (then we just
+ return lhs), force creation of a new SSA_NAME. */
+ if (changed || ((rhs1 != oe2->op || rhs2 != oe1->op) && opindex))
{
gimple insert_point = find_insert_point (stmt, oe1->op, oe2->op);
lhs = make_ssa_name (TREE_TYPE (lhs));
--- gcc/testsuite/gcc.c-torture/execute/pr65216.c.jj 2015-02-26
13:05:12.199816826 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr65216.c 2015-02-26
13:04:53.000000000 +0100
@@ -0,0 +1,20 @@
+/* PR tree-optimization/65216 */
+
+int a, b = 62, e;
+volatile int c, d;
+
+int
+main ()
+{
+ int f = 0;
+ for (a = 0; a < 2; a++)
+ {
+ b &= (8 ^ f) & 1;
+ for (e = 0; e < 6; e++)
+ if (c)
+ f = d;
+ }
+ if (b != 0)
+ __builtin_abort ();
+ return 0;
+}
Jakub
