Remove bogus assertion in pg_atomic_monotonic_advance_u64

This code wanted to ensure that the 'exchange' variable passed to
pg_atomic_compare_exchange_u64 has correct alignment, but apparently
platforms don't actually require anything that doesn't come naturally.

While messing with pg_atomic_monotonic_advance_u64: instead of using
Max() to determine the value to return, just use
pg_atomic_compare_exchange_u64()'s return value to decide; also, use
pg_atomic_compare_exchange_u64 instead of the _impl version; also remove
the unnecessary underscore at the end of variable name "target".

Backpatch to 17, where this code was introduced by commit bf3ff7bf83bc.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/36796438-a718-cf9b-2071-b2c1b947c1b5@gmail.com

1 files changed, 3 insertions, 0 deletions

diff --git a/src/include/port/atomics/generic-gcc.h b/src/include/port/atomics/generic-gcc.h
index 9d91370fa8c..872d2f02af4 100644
--- a/src/include/port/atomics/generic-gcc.h
+++ b/src/include/port/atomics/generic-gcc.h
@@ -240,6 +240,7 @@ static inline bool
 pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
 									uint64 *expected, uint64 newval)
 {
+	AssertPointerAlignment(expected, 8);
 	return __atomic_compare_exchange_n(&ptr->value, expected, newval, false,
 									   __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
 }
@@ -253,6 +254,8 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
 {
 	bool	ret;
 	uint64	current;
+
+	AssertPointerAlignment(expected, 8);
 	current = __sync_val_compare_and_swap(&ptr->value, *expected, newval);
 	ret = current == *expected;
 	*expected = current;