------- Additional Comments From aoliva at gcc dot gnu dot org 2005-04-02
16:59 -------
Subject: Re: [PR tree-optimization/20640] add phi args to dests of
dce-redirected edges
On Mar 31, 2005, Jeffrey A Law <[EMAIL PROTECTED]> wrote:
> On Thu, 2005-03-31 at 05:26 -0300, Alexandre Oliva wrote:
>> On Mar 31, 2005, Alexandre Oliva <[EMAIL PROTECTED]> wrote:
> [ ... ]
>> Anyway, how does this patch look?
>> Index: gcc/ChangeLog
> from Alexandre Oliva <[EMAIL PROTECTED]>
> PR tree-optimization/20640
> * tree-ssa-dce.c (remove_dead_stmt): Don't redirect edge to
> post-dominator if it has phi nodes.
> (eliminate_unnecessary_stmts): Remove dead phis in all blocks
> before dead statements.
> BTW, if you want to go forward with this version, it looks OK to me
> assuming it passes bootstrapping and regression testing.
It does, so I'm checking it in with a minor change: it doesn't make
sense to request the edge to be redirected to itself, since it's a
no-op, so I moved the call into the `else' branch of the new
conditional.
Thanks,
Index: gcc/ChangeLog
from Alexandre Oliva <[EMAIL PROTECTED]>
PR tree-optimization/20640
* tree-ssa-dce.c (remove_dead_stmt): Don't redirect edge to
post-dominator if it has phi nodes.
(eliminate_unnecessary_stmts): Remove dead phis in all blocks
before dead statements.
Index: gcc/tree-ssa-dce.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-ssa-dce.c,v
retrieving revision 2.37
diff -u -p -r2.37 tree-ssa-dce.c
--- gcc/tree-ssa-dce.c 12 Mar 2005 20:53:18 -0000 2.37
+++ gcc/tree-ssa-dce.c 1 Apr 2005 20:30:24 -0000
@@ -637,7 +637,10 @@ eliminate_unnecessary_stmts (void)
{
/* Remove dead PHI nodes. */
remove_dead_phis (bb);
+ }
+ FOR_EACH_BB (bb)
+ {
/* Remove dead statements. */
for (i = bsi_start (bb); ! bsi_end_p (i) ; )
{
@@ -724,6 +727,7 @@ remove_dead_stmt (block_stmt_iterator *i
if (is_ctrl_stmt (t))
{
basic_block post_dom_bb;
+
/* The post dominance info has to be up-to-date. */
gcc_assert (dom_computed[CDI_POST_DOMINATORS] == DOM_OK);
/* Get the immediate post dominator of bb. */
@@ -737,9 +741,20 @@ remove_dead_stmt (block_stmt_iterator *i
return;
}
- /* Redirect the first edge out of BB to reach POST_DOM_BB. */
- redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb);
- PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL;
+ /* If the post dominator block has PHI nodes, we might be unable
+ to compute the right PHI args for them. Since the control
+ statement is unnecessary, all edges can be regarded as
+ equivalent, but we have to get rid of the condition, since it
+ might reference a variable that was determined to be
+ unnecessary and thus removed. */
+ if (phi_nodes (post_dom_bb))
+ post_dom_bb = EDGE_SUCC (bb, 0)->dest;
+ else
+ {
+ /* Redirect the first edge out of BB to reach POST_DOM_BB. */
+ redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb);
+ PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL;
+ }
EDGE_SUCC (bb, 0)->probability = REG_BR_PROB_BASE;
EDGE_SUCC (bb, 0)->count = bb->count;
Index: gcc/testsuite/ChangeLog
from Alexandre Oliva <[EMAIL PROTECTED]>
PR tree-optimization/20640
* gcc.dg/torture/tree-loop-1.c: New.
Index: gcc/testsuite/gcc.dg/torture/tree-loop-1.c
===================================================================
RCS file: gcc/testsuite/gcc.dg/torture/tree-loop-1.c
diff -N gcc/testsuite/gcc.dg/torture/tree-loop-1.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ gcc/testsuite/gcc.dg/torture/tree-loop-1.c 30 Mar 2005 05:28:22 -0000
@@ -0,0 +1,21 @@
+/* PR tree-optimization/20640 */
+
+/* After unrolling the loop, we'd turn some conditional branches into
+ unconditional ones, but branch redirection would fail to compute
+ the PHI args for the PHI nodes in the replacement edge
+ destination, so they'd remain NULL causing crashes later on. */
+
+/* { dg-do compile } */
+
+static int a = 0;
+extern int foo (void);
+extern int *bar (void) __attribute__ ((__const__));
+
+void
+test (int x)
+{
+ int b = 10;
+ while (foo () == -1 && *bar () == 4 && b > 0)
+ --b;
+ a = x;
+}
--
Alexandre Oliva http://www.ic.unicamp.br/~oliva/
Red Hat Compiler Engineer [EMAIL PROTECTED], gcc.gnu.org}
Free Software Evangelist [EMAIL PROTECTED], gnu.org}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20640
