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

diff --git a/src/include/port/atomics.h b/src/include/port/atomics.h
index c911c6b9564daa8f7b4e66f0c045d3acbc6d16db..f6fa432d2dfde74f9930e0d2a450e6322fa2b0d3 100644 (file)
--- a/src/include/port/atomics.h
+++ b/src/include/port/atomics.h
@@ -507,7 +507,6 @@ pg_atomic_compare_exchange_u64(volatile pg_atomic_uint64 *ptr,
 {
 #ifndef PG_HAVE_ATOMIC_U64_SIMULATION
        AssertPointerAlignment(ptr, 8);
-       AssertPointerAlignment(expected, 8);
 #endif
        return pg_atomic_compare_exchange_u64_impl(ptr, expected, newval);
 }
@@ -576,7 +575,7 @@ pg_atomic_sub_fetch_u64(volatile pg_atomic_uint64 *ptr, int64 sub_)
  * Full barrier semantics (even when value is unchanged).
  */
 static inline uint64
-pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target_)
+pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target)
 {
        uint64          currval;
 
@@ -585,23 +584,19 @@ pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target_)
 #endif
 
        currval = pg_atomic_read_u64_impl(ptr);
-       if (currval >= target_)
+       if (currval >= target)
        {
                pg_memory_barrier();
                return currval;
        }
 
-#ifndef PG_HAVE_ATOMIC_U64_SIMULATION
-       AssertPointerAlignment(&currval, 8);
-#endif
-
-       while (currval < target_)
+       while (currval < target)
        {
-               if (pg_atomic_compare_exchange_u64_impl(ptr, &currval, target_))
-                       break;
+               if (pg_atomic_compare_exchange_u64(ptr, &currval, target))
+                       return target;
        }
 
-       return Max(target_, currval);
+       return currval;
 }
 
 #undef INSIDE_ATOMICS_H

diff --git a/src/include/port/atomics/arch-ppc.h b/src/include/port/atomics/arch-ppc.h
index 94ba2597fb7f1dd2faaa3e96fd77021ff2261d39..edaab7c8957fc626cd8fb9103187fd5244816191 100644 (file)
--- a/src/include/port/atomics/arch-ppc.h
+++ b/src/include/port/atomics/arch-ppc.h
@@ -173,6 +173,8 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
        uint32 condition_register;
        bool ret;
 
+       AssertPointerAlignment(expected, 8);
+
        /* Like u32, but s/lwarx/ldarx/; s/stwcx/stdcx/; s/cmpw/cmpd/ */
 #ifdef HAVE_I_CONSTRAINT__BUILTIN_CONSTANT_P
        if (__builtin_constant_p(*expected) &&

diff --git a/src/include/port/atomics/arch-x86.h b/src/include/port/atomics/arch-x86.h
index 3efa79dc3df3a67569843dfd1798556a4be3d93e..2a8eca30fcf9d0e58a0b225336d0efa5f1890450 100644 (file)
--- a/src/include/port/atomics/arch-x86.h
+++ b/src/include/port/atomics/arch-x86.h
@@ -207,6 +207,8 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
 {
        char    ret;
 
+       AssertPointerAlignment(expected, 8);
+
        /*
         * Perform cmpxchg and use the zero flag which it implicitly sets when
         * equal to measure the success.

diff --git a/src/include/port/atomics/generic-gcc.h b/src/include/port/atomics/generic-gcc.h
index 9d91370fa8cde316840248d1aefd5844d86acacb..872d2f02af4a2c37ac901f3b95e2fca4292ed597 100644 (file)
--- 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;

diff --git a/src/include/port/atomics/generic-sunpro.h b/src/include/port/atomics/generic-sunpro.h
index e060c0868a963ec2c8c0db97ff63949b33f909fc..840a45e7788c7484a91e7304f7b5dbdd0ce0fd7f 100644 (file)
--- a/src/include/port/atomics/generic-sunpro.h
+++ b/src/include/port/atomics/generic-sunpro.h
@@ -102,6 +102,7 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
        bool    ret;
        uint64  current;
 
+       AssertPointerAlignment(expected, 8);
        current = atomic_cas_64(&ptr->value, *expected, newval);
        ret = current == *expected;
        *expected = current;