PR ipa/103601: ICE compiling CSiBE in ipa-modref's insert_kill.

This patch fixes PR ipa/103061 which is P1 regression that shows up as
an ICE in ipa-modref-tree.c's insert_kill when compiling the CSiBE
benchmark.  I believe the underlying cause is that the new kill tracking
functionality wasn't anticipating memory accesses that are zero bits
wide!?.  The failing source code (test case) contains the unusual lines:
typedef struct { } spinlock_t;
and
q->lock = (spinlock_t) { };
Making spinlock_t larger, or removing the assignment work around the issue.

The one line patch below to useful_for_kill_p teaches IPA that a memory
write is only useful as a "kill" if it is more than zero bits wide.
In theory, the existing known_size_p (size) test is now redundant, as
poly_int64 currently uses the value -1 for unknown size values,
but the proposed change makes the semantics clear, and defends against
possible future changes in representation.

2021-12-10  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	PR ipa/103601
	* ipa-modref-tree.h (useful_for_kill_p): Zero width accesses aren't
	useful for kill tracking.

gcc/testsuite/ChangeLog
	PR ipa/103601
	* gcc.dg/ipa/pr103601.c: New test case.

1 files changed, 35 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/ipa/pr103601.c b/gcc/testsuite/gcc.dg/ipa/pr103601.c
new file mode 100644
index 0000000..7bdb5e5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/pr103601.c
@@ -0,0 +1,35 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fgnu89-inline" } */
+
+typedef struct { } spinlock_t;
+struct list_head {
+ struct list_head *next, *prev;
+};
+struct __wait_queue_head {
+ spinlock_t lock;
+ struct list_head task_list;
+};
+typedef struct __wait_queue_head wait_queue_head_t;
+static inline void init_waitqueue_head(wait_queue_head_t *q)
+{
+ q->lock = (spinlock_t) { };
+ do { (&q->task_list)->next = (&q->task_list); (&q->task_list)->prev = (&q->task_list); } while (0);
+}
+struct timer_list {
+ void (*function)(unsigned long);
+};
+struct rpc_task {
+ struct timer_list tk_timer;
+ wait_queue_head_t tk_wait;
+};
+static void
+rpc_run_timer(struct rpc_task *task)
+{
+}
+inline void
+rpc_init_task(struct rpc_task *task)
+{
+ task->tk_timer.function = (void (*)(unsigned long)) rpc_run_timer;
+ init_waitqueue_head(&task->tk_wait);
+}
+