Richard,
this (trunk) patch fixes PR62167.
The patch fixes a problem that triggers with the test-case on the 4.8 branch,
when tail-merge makes a dead type-unsafe load alive.
I'm not able to reproduce this bug on 4.9 and trunk with the same test-case. On
those branches, the tail-merge already does not happen.
The reason for the difference is as follows: With 4.8 the two phi arguments of
the phi in the tail block are value-numbered identically:
...
SCC consists of: p_14
Value numbering p_14 stmt = p_14 = MEM[(struct head *)_13].first;
Setting value number of p_14 to p_14 (changed)
SCC consists of: p_15
Value numbering p_15 stmt = p_15 = _13->next;
Setting value number of p_15 to p_14 (changed)
...
With 4.9 (and trunk), that's not the case:
...
SCC consists of: p_14
Value numbering p_14 stmt = p_14 = MEM[(struct head *)&heads][k.1_9].first;
Setting value number of p_14 to p_14 (changed)
SCC consists of: p_15
Value numbering p_15 stmt = p_15 = _13->next;
Setting value number of p_15 to p_15 (changed)
...
I'm not sure the bug triggers on trunk and 4.9, but I see no reason why it could
not trigger, so I'd prefer to apply the patch to 4.9 and trunk as well.
The patch introduces an xfail for pr51879-12.c. I can follow up with a patch to
improve upon that, but I think that's better limited to trunk only.
Bootstrapped and reg-tested on x86_64/trunk.
OK for trunk/stage3, 4.8, 4.9?
Thanks,
- Tom
2014-11-17 Tom de Vries <t...@codesourcery.com>
PR tree-optimization/62167
* tree-ssa-tail-merge.c (stmt_local_def): Handle statements with vuse
conservatively.
(gimple_equal_p): Don't use vn_valueize to compare for lhs equality of
assigns.
* gcc.dg/pr51879-12.c: Add xfails.
* gcc.dg/pr62167-run.c: New test.
* gcc.dg/pr62167.c: New test.
---
gcc/testsuite/gcc.dg/pr51879-12.c | 4 +--
gcc/testsuite/gcc.dg/pr62167-run.c | 47 +++++++++++++++++++++++++++++++++++
gcc/testsuite/gcc.dg/pr62167.c | 50 ++++++++++++++++++++++++++++++++++++++
gcc/tree-ssa-tail-merge.c | 6 +++--
4 files changed, 103 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/pr62167-run.c
create mode 100644 gcc/testsuite/gcc.dg/pr62167.c
diff --git a/gcc/testsuite/gcc.dg/pr51879-12.c b/gcc/testsuite/gcc.dg/pr51879-12.c
index 8126505..85e2687 100644
--- a/gcc/testsuite/gcc.dg/pr51879-12.c
+++ b/gcc/testsuite/gcc.dg/pr51879-12.c
@@ -24,6 +24,6 @@ foo (int y)
baz (a);
}
-/* { dg-final { scan-tree-dump-times "bar \\(" 1 "pre"} } */
-/* { dg-final { scan-tree-dump-times "bar2 \\(" 1 "pre"} } */
+/* { dg-final { scan-tree-dump-times "bar \\(" 1 "pre" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump-times "bar2 \\(" 1 "pre" { xfail *-*-* } } } */
/* { dg-final { cleanup-tree-dump "pre" } } */
diff --git a/gcc/testsuite/gcc.dg/pr62167-run.c b/gcc/testsuite/gcc.dg/pr62167-run.c
new file mode 100644
index 0000000..37214a3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr62167-run.c
@@ -0,0 +1,47 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -ftree-tail-merge" } */
+
+struct node
+{
+ struct node *next;
+ struct node *prev;
+};
+
+struct node node;
+
+struct head
+{
+ struct node *first;
+};
+
+struct head heads[5];
+
+int k = 2;
+
+struct head *head = &heads[2];
+
+int
+main ()
+{
+ struct node *p;
+
+ node.next = (void*)0;
+
+ node.prev = (void *)head;
+
+ head->first = &node;
+
+ struct node *n = head->first;
+
+ struct head *h = &heads[k];
+
+ heads[2].first = n->next;
+
+ if ((void*)n->prev == (void *)h)
+ p = h->first;
+ else
+ /* Dead tbaa-unsafe load from ((struct node *)&heads[2])->next. */
+ p = n->prev->next;
+
+ return !(p == (void*)0);
+}
diff --git a/gcc/testsuite/gcc.dg/pr62167.c b/gcc/testsuite/gcc.dg/pr62167.c
new file mode 100644
index 0000000..f8c31a0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr62167.c
@@ -0,0 +1,50 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-tail-merge -fdump-tree-pre" } */
+
+struct node
+{
+ struct node *next;
+ struct node *prev;
+};
+
+struct node node;
+
+struct head
+{
+ struct node *first;
+};
+
+struct head heads[5];
+
+int k = 2;
+
+struct head *head = &heads[2];
+
+int
+main ()
+{
+ struct node *p;
+
+ node.next = (void*)0;
+
+ node.prev = (void *)head;
+
+ head->first = &node;
+
+ struct node *n = head->first;
+
+ struct head *h = &heads[k];
+
+ heads[2].first = n->next;
+
+ if ((void*)n->prev == (void *)h)
+ p = h->first;
+ else
+ /* Dead tbaa-unsafe load from ((struct node *)&heads[2])->next. */
+ p = n->prev->next;
+
+ return !(p == (void*)0);
+}
+
+/* { dg-final { scan-tree-dump-not "Removing basic block" "pre"} } */
+/* { dg-final { cleanup-tree-dump "pre" } } */
diff --git a/gcc/tree-ssa-tail-merge.c b/gcc/tree-ssa-tail-merge.c
index 303bd5e..1651985 100644
--- a/gcc/tree-ssa-tail-merge.c
+++ b/gcc/tree-ssa-tail-merge.c
@@ -326,7 +326,8 @@ stmt_local_def (gimple stmt)
if (gimple_vdef (stmt) != NULL_TREE
|| gimple_has_side_effects (stmt)
- || gimple_could_trap_p_1 (stmt, false, false))
+ || gimple_could_trap_p_1 (stmt, false, false)
+ || gimple_vuse (stmt) != NULL_TREE)
return false;
def_p = SINGLE_SSA_DEF_OPERAND (stmt, SSA_OP_DEF);
@@ -1175,7 +1176,8 @@ gimple_equal_p (same_succ same_succ, gimple s1, gimple s2)
gimple_assign_rhs1 (s2)));
else if (TREE_CODE (lhs1) == SSA_NAME
&& TREE_CODE (lhs2) == SSA_NAME)
- return vn_valueize (lhs1) == vn_valueize (lhs2);
+ return operand_equal_p (gimple_assign_rhs1 (s1),
+ gimple_assign_rhs1 (s2), 0);
return false;
case GIMPLE_COND:
--
1.9.1
