Steven,
this patch fixes:
- PR62004 (the if-conversion pass part, the tail-merge part is still todo), and
- PR62030.
In both cases, a valid program with a dead type-unsafe access is transformed by
the if-conversion pass into an invalid program with a live type-unsafe access.
The transformation done by the if-conversion pass that suffers from this problem
is if-merging, replacing the if-then-else with the if-block or the then then-block.
The patch fixes this problem by detecting when the if-block and the then-block
are treated differently by alias analysis, and preventing the optimization in
that case.
This part of the patch fixes PR62004.
...
@@ -2583,7 +2631,7 @@ noce_process_if_block (struct noce_if_info *if_info)
/* Look and see if A and B are really the same. Avoid creating silly
cmove constructs that no one will fix up later. */
- if (rtx_equal_p (a, b))
+ if (rtx_interchangeable_p (a, b))
{
/* If we have an INSN_B, we don't have to create any new rtl. Just
move the instruction that we already have. If we don't have an
...
This part of the patch fixes PR62030:
...
@@ -2517,7 +2565,7 @@ noce_process_if_block (struct noce_if_info *if_info)
|| BLOCK_FOR_INSN (insn_b) != BLOCK_FOR_INSN (if_info->cond_earliest)
|| !NONJUMP_INSN_P (insn_b)
|| (set_b = single_set (insn_b)) == NULL_RTX
- || ! rtx_equal_p (x, SET_DEST (set_b))
+ || ! rtx_interchangeable_p (x, SET_DEST (set_b))
|| ! noce_operand_ok (SET_SRC (set_b))
|| reg_overlap_mentioned_p (x, SET_SRC (set_b))
|| modified_between_p (SET_SRC (set_b), insn_b, jump)
...
I've added the other fixes after review of the if-conversion pass for the same
problem, I hope this is complete (well, at least for the if-conversion pass. I
wonder if cross-jumping suffers from the same problem).
The PR62030 test-case fails with trunk on MIPS. The PR62004 testcase fails with
4.8 on x86_64. But I think the problem exists in trunk, 4.9 and 4.8, it's just
hard to trigger.
Bootstrapped and reg-tested on x86_64, trunk. No issue found other than
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62060 , which looks like a
test-case issue.
OK for trunk, 4.9, 4.8?
Thanks,
- Tom
2014-08-07 Tom de Vries <t...@codesourcery.com>
* ifcvt.c (mem_alias_equal_p, rtx_interchangeable_p): New function.
(noce_try_move, noce_process_if_block): Use rtx_interchangeable_p.
(noce_try_cmove_arith): Use mem_alias_equal_p.
* gcc.dg/pr62004.c: New test.
* gcc.dg/pr62030.c: Same.
* gcc.target/mips/pr62030-octeon.c: Same.
diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index faf9b30..6da3e0f 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -306,6 +306,52 @@ block_fallthru (basic_block bb)
return (e) ? e->dest : NULL_BLOCK;
}
+
+/* Return true if MEMs A and B are treated equal by alias analysis. */
+
+static bool
+mem_alias_equal_p (const_rtx a, const_rtx b)
+{
+ gcc_assert (GET_CODE (a) == MEM && GET_CODE (b) == MEM);
+
+ if (MEM_ADDR_SPACE (a) != MEM_ADDR_SPACE (b))
+ return false;
+
+ if (flag_strict_aliasing
+ && MEM_ALIAS_SET (a) != MEM_ALIAS_SET (b))
+ return false;
+
+ if (MEM_EXPR (a) != MEM_EXPR (b))
+ return false;
+
+ if (MEM_OFFSET_KNOWN_P (a) != MEM_OFFSET_KNOWN_P (b))
+ return false;
+
+ if (MEM_OFFSET_KNOWN_P (a)
+ && MEM_OFFSET (a) != MEM_OFFSET (b))
+ return false;
+
+ return true;
+}
+
+static bool
+rtx_interchangeable_p (const_rtx a, const_rtx b)
+{
+ if (!rtx_equal_p (a, b))
+ return false;
+
+ if (GET_CODE (a) != MEM)
+ return true;
+
+ /* A dead type-unsafe memory reference is legal, but a live type-unsafe memory
+ reference is not. Interchanging a dead type-unsafe memory reference with
+ a live type-safe one creates a live type-unsafe memory reference, in other
+ words, it makes the program illegal. So we check whether the two memory
+ references have equal tbaa properties. */
+
+ return mem_alias_equal_p (a, b);
+}
+
/* Go through a bunch of insns, converting them to conditional
execution format if possible. Return TRUE if all of the non-note
@@ -1034,6 +1080,9 @@ noce_try_move (struct noce_if_info *if_info)
|| (rtx_equal_p (if_info->a, XEXP (cond, 1))
&& rtx_equal_p (if_info->b, XEXP (cond, 0))))
{
+ if (!rtx_interchangeable_p (if_info->a, if_info->b))
+ return FALSE;
+
y = (code == EQ) ? if_info->a : if_info->b;
/* Avoid generating the move if the source is the destination. */
@@ -1537,14 +1586,13 @@ noce_try_cmove_arith (struct noce_if_info *if_info)
int insn_cost;
enum rtx_code code;
- /* A conditional move from two memory sources is equivalent to a
- conditional on their addresses followed by a load. Don't do this
- early because it'll screw alias analysis. Note that we've
- already checked for no side effects. */
- /* ??? FIXME: Magic number 5. */
+ /* A conditional move from two memory sources is equivalent to a conditional
+ on their addresses followed by a load. Don't do this if it'll screw alias
+ analysis. Note that we've already checked for no side effects. */
if (cse_not_expected
&& MEM_P (a) && MEM_P (b)
- && MEM_ADDR_SPACE (a) == MEM_ADDR_SPACE (b)
+ && mem_alias_equal_p (a, b)
+ /* ??? FIXME: Magic number 5. */
&& if_info->branch_cost >= 5)
{
enum machine_mode address_mode = get_address_mode (a);
@@ -2504,7 +2552,7 @@ noce_process_if_block (struct noce_if_info *if_info)
if (! insn_b
|| insn_b != last_active_insn (else_bb, FALSE)
|| (set_b = single_set (insn_b)) == NULL_RTX
- || ! rtx_equal_p (x, SET_DEST (set_b)))
+ || ! rtx_interchangeable_p (x, SET_DEST (set_b)))
return FALSE;
}
else
@@ -2517,7 +2565,7 @@ noce_process_if_block (struct noce_if_info *if_info)
|| BLOCK_FOR_INSN (insn_b) != BLOCK_FOR_INSN (if_info->cond_earliest)
|| !NONJUMP_INSN_P (insn_b)
|| (set_b = single_set (insn_b)) == NULL_RTX
- || ! rtx_equal_p (x, SET_DEST (set_b))
+ || ! rtx_interchangeable_p (x, SET_DEST (set_b))
|| ! noce_operand_ok (SET_SRC (set_b))
|| reg_overlap_mentioned_p (x, SET_SRC (set_b))
|| modified_between_p (SET_SRC (set_b), insn_b, jump)
@@ -2583,7 +2631,7 @@ noce_process_if_block (struct noce_if_info *if_info)
/* Look and see if A and B are really the same. Avoid creating silly
cmove constructs that no one will fix up later. */
- if (rtx_equal_p (a, b))
+ if (rtx_interchangeable_p (a, b))
{
/* If we have an INSN_B, we don't have to create any new rtl. Just
move the instruction that we already have. If we don't have an
diff --git a/gcc/testsuite/gcc.dg/pr62004.c b/gcc/testsuite/gcc.dg/pr62004.c
new file mode 100644
index 0000000..7292c4f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr62004.c
@@ -0,0 +1,47 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fno-tree-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/pr62030.c b/gcc/testsuite/gcc.dg/pr62030.c
new file mode 100644
index 0000000..a16a970
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr62030.c
@@ -0,0 +1,50 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+extern void abort (void);
+
+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];
+
+static int __attribute__((noinline))
+foo (void)
+{
+ node.prev = (void *)head;
+ head->first = &node;
+
+ struct node *n = head->first;
+ struct head *h = &heads[k];
+ struct node *next = n->next;
+
+ if (n->prev == (void *)h)
+ h->first = next;
+ else
+ n->prev->next = next;
+
+ n->next = h->first;
+ return n->next == &node;
+}
+
+int
+main (void)
+{
+ if (foo ())
+ abort ();
+ return 0;
+}
diff --git a/gcc/testsuite/gcc.target/mips/pr62030-octeon.c b/gcc/testsuite/gcc.target/mips/pr62030-octeon.c
new file mode 100644
index 0000000..2f86f5e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/mips/pr62030-octeon.c
@@ -0,0 +1,50 @@
+/* { dg-do run } */
+/* { dg-options "-march=octeon" } */
+
+extern void abort (void);
+
+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];
+
+static int __attribute__((noinline))
+foo (void)
+{
+ node.prev = (void *)head;
+ head->first = &node;
+
+ struct node *n = head->first;
+ struct head *h = &heads[k];
+ struct node *next = n->next;
+
+ if (n->prev == (void *)h)
+ h->first = next;
+ else
+ n->prev->next = next;
+
+ n->next = h->first;
+ return n->next == &node;
+}
+
+int
+main (void)
+{
+ if (foo ())
+ abort ();
+ return 0;
+}
--
1.9.1
