Hi!
For debug stmt uses, we don't want any PHI nodes to be created
just because of them, so the debug uses need to be ignored
during decisions which PHI nodes to add.
Unfortunately that means get_current_def can't be always trusted.
The following patch trusts it in a few cases where I'm reasonably
sure it is trustable. Perhaps some more cases could be added in
the future if anyone has ideas...
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2011-07-01 Jakub Jelinek <ja...@redhat.com>
PR debug/49602
* tree-into-ssa.c (rewrite_debug_stmt_uses): Disregard
get_current_def return value if it can't be trusted to be
the current value of the variable in the current bb.
* gcc.dg/pr49602.c: New test.
--- gcc/tree-into-ssa.c.jj 2011-06-23 10:13:58.000000000 +0200
+++ gcc/tree-into-ssa.c 2011-07-01 20:39:40.000000000 +0200
@@ -1343,7 +1343,41 @@ rewrite_debug_stmt_uses (gimple stmt)
}
}
else
- def = get_current_def (var);
+ {
+ def = get_current_def (var);
+ /* Check if get_current_def can be trusted. */
+ if (def)
+ {
+ basic_block bb = gimple_bb (stmt);
+ basic_block def_bb
+ = SSA_NAME_IS_DEFAULT_DEF (def)
+ ? NULL : gimple_bb (SSA_NAME_DEF_STMT (def));
+
+ /* If definition is in current bb, it is fine. */
+ if (bb == def_bb)
+ ;
+ /* If definition bb doesn't dominate the current bb,
+ it can't be used. */
+ else if (def_bb && !dominated_by_p (CDI_DOMINATORS, bb, def_bb))
+ def = NULL;
+ /* If there is just one definition and dominates the current
+ bb, it is fine. */
+ else if (get_phi_state (var) == NEED_PHI_STATE_NO)
+ ;
+ else
+ {
+ struct def_blocks_d *db_p = get_def_blocks_for (var);
+
+ /* If there are some non-debug uses in the current bb,
+ it is fine. */
+ if (bitmap_bit_p (db_p->livein_blocks, bb->index))
+ ;
+ /* Otherwise give up for now. */
+ else
+ def = NULL;
+ }
+ }
+ }
if (def == NULL)
{
gimple_debug_bind_reset_value (stmt);
--- gcc/testsuite/gcc.dg/pr49602.c.jj 2011-07-01 20:42:44.000000000 +0200
+++ gcc/testsuite/gcc.dg/pr49602.c 2011-07-01 18:49:04.000000000 +0200
@@ -0,0 +1,17 @@
+/* PR debug/49602 */
+/* { dg-do compile } */
+/* { dg-options "-g -O2" } */
+
+static void
+foo (int *x)
+{
+}
+
+void
+bar (int *x)
+{
+ int i;
+ for (i = 0; i == 1; ++i)
+ x = 0;
+ foo (x);
+}
Jakub
