[v2] LoongArch: Fix atomic_exchange expanding [PR107713]
Commit Message
We used to expand atomic_exchange_n(ptr, new, mem_order) for subword types
into something like:
{
__typeof__(*ptr) t = atomic_load_n(ptr, mem_order);
atomic_compare_exchange_n(ptr, &t, new, true, mem_order, mem_order);
return t;
}
It's incorrect because another thread may store a different value into *ptr
after atomic_load_n. Then atomic_compare_exchange_n will not store into
*ptr, but atomic_exchange_n should always perform the store.
gcc/ChangeLog:
PR target/107713
* config/loongarch/sync.md
(atomic_cas_value_exchange_7_<mode>): New define_insn.
(atomic_exchange): Use atomic_cas_value_exchange_7_si instead of
atomic_cas_value_cmp_and_7_si.
gcc/testsuite/ChangeLog:
PR target/107713
* gcc.target/loongarch/pr107713-1.c: New test.
* gcc.target/loongarch/pr107713-2.c: New test.
---
Thanks Ruoyao who helped me with community works, improved the submit
message and gave a more straightforward test.
Thanks Pei who gave me a further understanding of ll-sc offline.
gcc/config/loongarch/sync.md | 27 +++++++++-
.../gcc.target/loongarch/pr107713-1.c | 50 +++++++++++++++++++
.../gcc.target/loongarch/pr107713-2.c | 9 ++++
3 files changed, 84 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/loongarch/pr107713-1.c
create mode 100644 gcc/testsuite/gcc.target/loongarch/pr107713-2.c
@@ -448,6 +448,29 @@
}
[(set (attr "length") (const_int 32))])
+(define_insn "atomic_cas_value_exchange_7_<mode>"
+ [(set (match_operand:GPR 0 "register_operand" "=&r")
+ (match_operand:GPR 1 "memory_operand" "+ZC"))
+ (set (match_dup 1)
+ (unspec_volatile:GPR [(match_operand:GPR 2 "reg_or_0_operand" "rJ")
+ (match_operand:GPR 3 "reg_or_0_operand" "rJ")
+ (match_operand:GPR 4 "reg_or_0_operand" "rJ")
+ (match_operand:GPR 5 "reg_or_0_operand" "rJ")
+ (match_operand:SI 6 "const_int_operand")] ;; model
+ UNSPEC_SYNC_EXCHANGE))
+ (clobber (match_scratch:GPR 7 "=&r"))]
+ ""
+{
+ return "%G6\\n\\t"
+ "1:\\n\\t"
+ "ll.<amo>\\t%0,%1\\n\\t"
+ "and\\t%7,%0,%z3\\n\\t"
+ "or%i5\\t%7,%7,%5\\n\\t"
+ "sc.<amo>\\t%7,%1\\n\\t"
+ "beqz\\t%7,1b\\n\\t";
+}
+ [(set (attr "length") (const_int 20))])
+
(define_expand "atomic_exchange<mode>"
[(set (match_operand:SHORT 0 "register_operand")
(unspec_volatile:SHORT
@@ -459,9 +482,9 @@
""
{
union loongarch_gen_fn_ptrs generator;
- generator.fn_7 = gen_atomic_cas_value_cmp_and_7_si;
+ generator.fn_7 = gen_atomic_cas_value_exchange_7_si;
loongarch_expand_atomic_qihi (generator, operands[0], operands[1],
- operands[1], operands[2], operands[3]);
+ const0_rtx, operands[2], operands[3]);
DONE;
})
new file mode 100644
@@ -0,0 +1,50 @@
+/* { dg-do run } */
+/* { dg-require-effective-target pthread } */
+/* { dg-options "-pthread" } */
+
+#include <pthread.h>
+
+char x, x1, x2;
+
+void *
+work1 (void *)
+{
+ for (int i = 0; i < 100; i++)
+ x1 = __atomic_exchange_n (&x, x1, __ATOMIC_SEQ_CST);
+ return NULL;
+}
+
+void *
+work2 (void *)
+{
+ for (int i = 0; i < 100; i++)
+ x2 = __atomic_exchange_n (&x, x2, __ATOMIC_SEQ_CST);
+ return NULL;
+}
+
+void
+test (void)
+{
+ x = 0;
+ x1 = 1;
+ x2 = 2;
+ pthread_t w1, w2;
+ if (pthread_create (&w1, NULL, work1, NULL) != 0)
+ __builtin_abort ();
+ if (pthread_create (&w2, NULL, work2, NULL) != 0)
+ __builtin_abort ();
+ if (pthread_join (w1, NULL) != 0)
+ __builtin_abort ();
+ if (pthread_join (w2, NULL) != 0)
+ __builtin_abort ();
+ if ((x ^ x1 ^ x2) != 3)
+ __builtin_abort ();
+}
+
+int
+main ()
+{
+ int i;
+ for (i = 0; i < 10000; i++)
+ test ();
+}
new file mode 100644
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-final { scan-assembler-times "beq|bne" 1 } } */
+
+char
+t (char *p, char x)
+{
+ return __atomic_exchange_n (p, x, __ATOMIC_RELAXED);
+}