diff --git a/cmd/ztest/ztest.c b/cmd/ztest/ztest.c
index 102f7220e9..4da772d3a9 100644
--- a/cmd/ztest/ztest.c
+++ b/cmd/ztest/ztest.c
@@ -1163,7 +1163,7 @@ ztest_vdev_attach_detach(ztest_args_t *za)
 vdev_t *
 grow_vdev(vdev_t *vd, void *arg)
 {
-	spa_t *spa = vd->vdev_spa;
+	ASSERTV(spa_t *spa = vd->vdev_spa);
 	size_t *newsize = arg;
 	size_t fsize;
 	int fd;
diff --git a/module/nvpair/nvpair.c b/module/nvpair/nvpair.c
index a3e624d408..c3bd85c212 100644
--- a/module/nvpair/nvpair.c
+++ b/module/nvpair/nvpair.c
@@ -1560,7 +1560,7 @@ nvlist_lookup_nvpair_ei_sep(nvlist_t *nvl, const char *name, const char sep,
 {
 	nvpair_t	*nvp;
 	const char	*np;
-	char		*sepp = NULL;
+	char		*sepp;
 	char		*idxp, *idxep;
 	nvlist_t	**nva;
 	long		idx = 0;
diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
index 8f9869f3f3..65b14f5369 100644
--- a/module/zfs/dbuf.c
+++ b/module/zfs/dbuf.c
@@ -323,12 +323,12 @@ dbuf_verify(dmu_buf_impl_t *db)
 	 * dnode_set_blksz().
 	 */
 	if (db->db_level == 0 && db->db.db_object == DMU_META_DNODE_OBJECT) {
+		ASSERTV(dbuf_dirty_record_t *dr = db->db_data_pending);
 		/*
 		 * It should only be modified in syncing context, so
 		 * make sure we only have one copy of the data.
 		 */
-		ASSERT(db->db_data_pending == NULL ||
-		       db->db_data_pending->dt.dl.dr_data == db->db_buf);
+		ASSERT(dr == NULL || dr->dt.dl.dr_data == db->db_buf);
 	}
 
 	/* verify db->db_blkptr */
@@ -344,6 +344,8 @@ dbuf_verify(dmu_buf_impl_t *db)
 			    &dn->dn_phys->dn_blkptr[db->db_blkid]);
 		} else {
 			/* db is pointed to by an indirect block */
+			ASSERTV(int epb = db->db_parent->db.db_size >>
+				SPA_BLKPTRSHIFT);
 			ASSERT3U(db->db_parent->db_level, ==, db->db_level+1);
 			ASSERT3U(db->db_parent->db.db_object, ==,
 			    db->db.db_object);
@@ -355,9 +357,7 @@ dbuf_verify(dmu_buf_impl_t *db)
 			if (RW_WRITE_HELD(&db->db_dnode->dn_struct_rwlock)) {
 				ASSERT3P(db->db_blkptr, ==,
 				    ((blkptr_t *)db->db_parent->db.db_data +
-				    db->db_blkid %
-				    (db->db_parent->db.db_size >>
-				    SPA_BLKPTRSHIFT)));
+				    db->db_blkid % epb));
 			}
 		}
 	}
@@ -370,10 +370,11 @@ dbuf_verify(dmu_buf_impl_t *db)
 		 * data when we evict this buffer.
 		 */
 		if (db->db_dirtycnt == 0) {
+			ASSERTV(uint64_t *buf = db->db.db_data);
 			int i;
 
 			for (i = 0; i < db->db.db_size >> 3; i++) {
-				ASSERT(((uint64_t *)db->db.db_data)[i] == 0);
+				ASSERT(buf[i] == 0);
 			}
 		}
 	}
@@ -1801,7 +1802,8 @@ dbuf_create_bonus(dnode_t *dn)
 void
 dbuf_add_ref(dmu_buf_impl_t *db, void *tag)
 {
-	VERIFY(refcount_add(&db->db_holds, tag) > 1);
+	ASSERTV(int64_t holds = refcount_add(&db->db_holds, tag));
+	ASSERT(holds > 1);
 }
 
 #pragma weak dmu_buf_rele = dbuf_rele
@@ -2407,15 +2409,17 @@ dbuf_write_done(zio_t *zio, arc_buf_t *buf, void *vdb)
 				ASSERT(arc_released(db->db_buf));
 		}
 	} else {
+		ASSERTV(dnode_t *dn = db->db_dnode);
+
 		ASSERT(list_head(&dr->dt.di.dr_children) == NULL);
-		ASSERT3U(db->db.db_size, ==,
-			 1<<db->db_dnode->dn_phys->dn_indblkshift);
+		ASSERT3U(db->db.db_size, ==, 1<<dn->dn_phys->dn_indblkshift);
 		if (!BP_IS_HOLE(db->db_blkptr)) {
+			ASSERTV(int epbs = dn->dn_phys->dn_indblkshift -
+			    SPA_BLKPTRSHIFT);
 			ASSERT3U(BP_GET_LSIZE(db->db_blkptr), ==,
 			    db->db.db_size);
-			ASSERT3U(db->db_dnode->dn_phys->dn_maxblkid >> (db->db_level *
-			    (db->db_dnode->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT)),
-		            >=, db->db_blkid);
+			ASSERT3U(dn->dn_phys->dn_maxblkid
+			    >> (db->db_level * epbs), >=, db->db_blkid);
 			arc_set_callback(db->db_buf, dbuf_do_evict, db);
 		}
 		mutex_destroy(&dr->dt.di.dr_mtx);
diff --git a/module/zfs/dmu.c b/module/zfs/dmu.c
index 9e63afd0df..19bf695f1f 100644
--- a/module/zfs/dmu.c
+++ b/module/zfs/dmu.c
@@ -879,8 +879,10 @@ dmu_sync_ready(zio_t *zio, arc_buf_t *buf, void *varg)
 	blkptr_t *bp = zio->io_bp;
 
 	if (!BP_IS_HOLE(bp)) {
-		ASSERT(BP_GET_TYPE(bp) == ((dmu_sync_arg_t *)
-		       varg)->dr->dr_dbuf->db_dnode->dn_type);
+		ASSERTV(dmu_sync_arg_t *in = varg);
+		ASSERTV(dbuf_dirty_record_t *dr = in->dr);
+		ASSERTV(dmu_buf_impl_t *db = dr->dr_dbuf);
+		ASSERT(BP_GET_TYPE(bp) == db->db_dnode->dn_type);
 		ASSERT(BP_GET_LEVEL(bp) == 0);
 		bp->blk_fill = 1;
 	}
diff --git a/module/zfs/dmu_objset.c b/module/zfs/dmu_objset.c
index d1cd9d5307..d6ad530fdf 100644
--- a/module/zfs/dmu_objset.c
+++ b/module/zfs/dmu_objset.c
@@ -893,9 +893,9 @@ ready(zio_t *zio, arc_buf_t *abuf, void *arg)
 	int i;
 
 	blkptr_t *bp = zio->io_bp;
-	blkptr_t *bp_orig = &zio->io_bp_orig;
 	objset_impl_t *os = arg;
 	dnode_phys_t *dnp = &os->os_phys->os_meta_dnode;
+	ASSERTV(blkptr_t *bp_orig = &zio->io_bp_orig);
 
 	ASSERT(bp == os->os_rootbp);
 	ASSERT(BP_GET_TYPE(bp) == DMU_OT_OBJSET);
@@ -912,7 +912,7 @@ ready(zio_t *zio, arc_buf_t *abuf, void *arg)
 		bp->blk_fill += dnp->dn_blkptr[i].blk_fill;
 
 	if (zio->io_flags & ZIO_FLAG_IO_REWRITE) {
-		VERIFY(DVA_EQUAL(BP_IDENTITY(bp), BP_IDENTITY(bp_orig)));
+		ASSERT(DVA_EQUAL(BP_IDENTITY(bp), BP_IDENTITY(bp_orig)));
 	} else {
 		if (zio->io_bp_orig.blk_birth == os->os_synctx->tx_txg)
 			(void) dsl_dataset_block_kill(os->os_dsl_dataset,
@@ -1040,7 +1040,7 @@ dmu_objset_do_userquota_callbacks(objset_impl_t *os, dmu_tx_t *tx)
 {
 	dnode_t *dn;
 	list_t *list = &os->os_synced_dnodes;
-	static const char zerobuf[DN_MAX_BONUSLEN] = {0};
+	ASSERTV(static const char zerobuf[DN_MAX_BONUSLEN] = {0});
 
 	ASSERT(list_head(list) == NULL || dmu_objset_userused_enabled(os));
 
diff --git a/module/zfs/dnode.c b/module/zfs/dnode.c
index d80d4f9af9..97e670cfb6 100644
--- a/module/zfs/dnode.c
+++ b/module/zfs/dnode.c
@@ -40,9 +40,7 @@ static int free_range_compar(const void *node1, const void *node2);
 
 static kmem_cache_t *dnode_cache;
 
-#ifndef NDEBUG
-static dnode_phys_t dnode_phys_zero;
-#endif
+ASSERTV(static dnode_phys_t dnode_phys_zero);
 
 int zfs_default_bs = SPA_MINBLOCKSHIFT;
 int zfs_default_ibs = DN_MAX_INDBLKSHIFT;
diff --git a/module/zfs/dnode_sync.c b/module/zfs/dnode_sync.c
index 72e469f727..f14e70f7f2 100644
--- a/module/zfs/dnode_sync.c
+++ b/module/zfs/dnode_sync.c
@@ -317,10 +317,8 @@ dnode_sync_free_range(dnode_t *dn, uint64_t blkid, uint64_t nblks, dmu_tx_t *tx)
 		ASSERT3U(blkid + nblks, <=, dn->dn_phys->dn_nblkptr);
 		(void) free_blocks(dn, bp + blkid, nblks, tx);
 		if (trunc) {
-#ifndef NDEBUG
-			uint64_t off = (dn->dn_phys->dn_maxblkid + 1) *
-			    (dn->dn_phys->dn_datablkszsec << SPA_MINBLOCKSHIFT);
-#endif
+			ASSERTV(uint64_t off = (dn->dn_phys->dn_maxblkid + 1) *
+			    (dn->dn_phys->dn_datablkszsec<<SPA_MINBLOCKSHIFT));
 			dn->dn_phys->dn_maxblkid = (blkid ? blkid - 1 : 0);
 			ASSERT(off < dn->dn_phys->dn_maxblkid ||
 			    dn->dn_phys->dn_maxblkid == 0 ||
@@ -349,10 +347,8 @@ dnode_sync_free_range(dnode_t *dn, uint64_t blkid, uint64_t nblks, dmu_tx_t *tx)
 		dbuf_rele(db, FTAG);
 	}
 	if (trunc) {
-#ifndef NDEBUG
-		uint64_t off = (dn->dn_phys->dn_maxblkid + 1) *
-		    (dn->dn_phys->dn_datablkszsec << SPA_MINBLOCKSHIFT);
-#endif
+		ASSERTV(uint64_t off = (dn->dn_phys->dn_maxblkid + 1) *
+		    (dn->dn_phys->dn_datablkszsec << SPA_MINBLOCKSHIFT));
 		dn->dn_phys->dn_maxblkid = (blkid ? blkid - 1 : 0);
 		ASSERT(off < dn->dn_phys->dn_maxblkid ||
 		    dn->dn_phys->dn_maxblkid == 0 ||
@@ -522,7 +518,7 @@ dnode_sync(dnode_t *dn, dmu_tx_t *tx)
 	dnode_phys_t *dnp = dn->dn_phys;
 	int txgoff = tx->tx_txg & TXG_MASK;
 	list_t *list = &dn->dn_dirty_records[txgoff];
-	static const dnode_phys_t zerodn = { 0 };
+	ASSERTV(static const dnode_phys_t zerodn = { 0 });
 
 	ASSERT(dmu_tx_is_syncing(tx));
 	ASSERT(dnp->dn_type != DMU_OT_NONE || dn->dn_allocated_txg);
diff --git a/module/zfs/dsl_dataset.c b/module/zfs/dsl_dataset.c
index 11044a6250..be8ce684af 100644
--- a/module/zfs/dsl_dataset.c
+++ b/module/zfs/dsl_dataset.c
@@ -991,7 +991,7 @@ dsl_dataset_destroy(dsl_dataset_t *ds, void *tag)
 	 */
 	if (ds->ds_phys->ds_bp.blk_fill == 0 &&
 	    dmu_objset_userused_enabled(os->os)) {
-		uint64_t count;
+		ASSERTV(uint64_t count);
 
 		ASSERT(zap_count(os, DMU_USERUSED_OBJECT, &count) != 0 ||
 		    count == 0);
@@ -1728,8 +1728,8 @@ dsl_dataset_destroy_sync(void *arg1, void *tag, cred_t *cr, dmu_tx_t *tx)
 	    cr, "dataset = %llu", ds->ds_object);
 
 	if (ds->ds_phys->ds_next_clones_obj != 0) {
-		uint64_t count;
-		VERIFY(0 == zap_count(mos,
+		ASSERTV(uint64_t count);
+		ASSERT(0 == zap_count(mos,
 		    ds->ds_phys->ds_next_clones_obj, &count) && count == 0);
 		VERIFY(0 == dmu_object_free(mos,
 		    ds->ds_phys->ds_next_clones_obj, tx));
@@ -2030,8 +2030,10 @@ dsl_dataset_space(dsl_dataset_t *ds,
 boolean_t
 dsl_dataset_modified_since_lastsnap(dsl_dataset_t *ds)
 {
-	ASSERT(RW_LOCK_HELD(&(ds->ds_dir->dd_pool)->dp_config_rwlock) ||
-	    dsl_pool_sync_context(ds->ds_dir->dd_pool));
+	ASSERTV(dsl_pool_t *dp = ds->ds_dir->dd_pool);
+
+	ASSERT(RW_LOCK_HELD(&dp->dp_config_rwlock) ||
+	    dsl_pool_sync_context(dp));
 	if (ds->ds_prev == NULL)
 		return (B_FALSE);
 	if (ds->ds_phys->ds_bp.blk_birth >
diff --git a/module/zfs/dsl_dir.c b/module/zfs/dsl_dir.c
index 9238777ff6..e3be20d80e 100644
--- a/module/zfs/dsl_dir.c
+++ b/module/zfs/dsl_dir.c
@@ -48,10 +48,11 @@ static void
 dsl_dir_evict(dmu_buf_t *db, void *arg)
 {
 	dsl_dir_t *dd = arg;
+	ASSERTV(dsl_pool_t *dp = dd->dd_pool;)
 	int t;
 
 	for (t = 0; t < TXG_SIZE; t++) {
-		ASSERT(!txg_list_member(&dd->dd_pool->dp_dirty_dirs, dd, t));
+		ASSERT(!txg_list_member(&dp->dp_dirty_dirs, dd, t));
 		ASSERT(dd->dd_tempreserved[t] == 0);
 		ASSERT(dd->dd_space_towrite[t] == 0);
 	}
diff --git a/module/zfs/dsl_prop.c b/module/zfs/dsl_prop.c
index c26c3ff270..526fb5cc43 100644
--- a/module/zfs/dsl_prop.c
+++ b/module/zfs/dsl_prop.c
@@ -368,7 +368,7 @@ dsl_prop_set_sync(void *arg1, void *arg2, cred_t *cr, dmu_tx_t *tx)
 
 	if (psa->numints == 0) {
 		int err = zap_remove(mos, zapobj, psa->name, tx);
-		VERIFY(0 == err || ENOENT == err);
+		VERIFY(err == 0 || err == ENOENT);
 		if (isint) {
 			VERIFY(0 == dsl_prop_get_ds(ds,
 			    psa->name, 8, 1, &intval, NULL));
diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index 139a670d4c..e13ef765a1 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -3004,6 +3004,7 @@ int
 spa_vdev_attach(spa_t *spa, uint64_t guid, nvlist_t *nvroot, int replacing)
 {
 	uint64_t txg, open_txg;
+	ASSERTV(vdev_t *rvd = spa->spa_root_vdev;)
 	vdev_t *oldvd, *newvd, *newrootvd, *pvd, *tvd;
 	vdev_ops_t *pvops;
 	dmu_tx_t *tx;
@@ -3120,7 +3121,7 @@ spa_vdev_attach(spa_t *spa, uint64_t guid, nvlist_t *nvroot, int replacing)
 	if (pvd->vdev_ops != pvops)
 		pvd = vdev_add_parent(oldvd, pvops);
 
-	ASSERT(pvd->vdev_top->vdev_parent == spa->spa_root_vdev);
+	ASSERT(pvd->vdev_top->vdev_parent == rvd);
 	ASSERT(pvd->vdev_ops == pvops);
 	ASSERT(oldvd->vdev_parent == pvd);
 
@@ -3133,7 +3134,7 @@ spa_vdev_attach(spa_t *spa, uint64_t guid, nvlist_t *nvroot, int replacing)
 
 	tvd = newvd->vdev_top;
 	ASSERT(pvd->vdev_top == tvd);
-	ASSERT(tvd->vdev_parent == spa->spa_root_vdev);
+	ASSERT(tvd->vdev_parent == rvd);
 
 	vdev_config_dirty(tvd);
 
@@ -3195,6 +3196,7 @@ spa_vdev_detach(spa_t *spa, uint64_t guid, uint64_t pguid, int replace_done)
 {
 	uint64_t txg;
 	int error;
+	ASSERTV(vdev_t *rvd = spa->spa_root_vdev;)
 	vdev_t *vd, *pvd, *cvd, *tvd;
 	boolean_t unspare = B_FALSE;
 	uint64_t unspare_guid = 0;
@@ -3339,7 +3341,7 @@ spa_vdev_detach(spa_t *spa, uint64_t guid, uint64_t pguid, int replace_done)
 	 * may have been the previous top-level vdev.
 	 */
 	tvd = cvd->vdev_top;
-	ASSERT(tvd->vdev_parent == spa->spa_root_vdev);
+	ASSERT(tvd->vdev_parent == rvd);
 
 	/*
 	 * Reevaluate the parent vdev state.
diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index 641e059870..63f7a83f30 100644
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -1252,8 +1252,9 @@ vdev_validate(vdev_t *vd)
 void
 vdev_close(vdev_t *vd)
 {
-	ASSERT(spa_config_held(vd->vdev_spa, SCL_STATE_ALL, RW_WRITER) ==
-	       SCL_STATE_ALL);
+	ASSERTV(spa_t *spa = vd->vdev_spa);
+
+	ASSERT(spa_config_held(spa, SCL_STATE_ALL, RW_WRITER) == SCL_STATE_ALL);
 
 	vd->vdev_ops->vdev_op_close(vd);
 
diff --git a/module/zfs/vdev_cache.c b/module/zfs/vdev_cache.c
index b02821b66a..9fbea035df 100644
--- a/module/zfs/vdev_cache.c
+++ b/module/zfs/vdev_cache.c
@@ -246,6 +246,7 @@ vdev_cache_read(zio_t *zio)
 	vdev_cache_t *vc = &zio->io_vd->vdev_cache;
 	vdev_cache_entry_t *ve, ve_search;
 	uint64_t cache_offset = P2ALIGN(zio->io_offset, VCBS);
+	ASSERTV(uint64_t cache_phase = P2PHASE(zio->io_offset, VCBS);)
 	zio_t *fio;
 
 	ASSERT(zio->io_type == ZIO_TYPE_READ);
@@ -262,7 +263,7 @@ vdev_cache_read(zio_t *zio)
 	if (P2BOUNDARY(zio->io_offset, zio->io_size, VCBS))
 		return (EXDEV);
 
-	ASSERT(P2PHASE(zio->io_offset, VCBS) + zio->io_size <= VCBS);
+	ASSERT(cache_phase + zio->io_size <= VCBS);
 
 	mutex_enter(&vc->vc_lock);
 
diff --git a/module/zfs/zap_micro.c b/module/zfs/zap_micro.c
index 50ef434182..891c948da1 100644
--- a/module/zfs/zap_micro.c
+++ b/module/zfs/zap_micro.c
@@ -747,8 +747,8 @@ mzap_addent(zap_name_t *zn, uint64_t value)
 
 #ifdef ZFS_DEBUG
 	for (i = 0; i < zap->zap_m.zap_num_chunks; i++) {
-		ASSERT(strcmp(zn->zn_name_orij,
-		       (&zap->zap_m.zap_phys->mz_chunk[i])->mze_name) != 0);
+		ASSERTV(mzap_ent_phys_t *mze=&zap->zap_m.zap_phys->mz_chunk[i]);
+		ASSERT(strcmp(zn->zn_name_orij, mze->mze_name) != 0);
 	}
 #endif
 
diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index f3f328c00c..a21efa7945 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -1515,7 +1515,7 @@ static void
 zio_write_gang_member_ready(zio_t *zio)
 {
 	zio_t *pio = zio_unique_parent(zio);
-	zio_t *gio = zio->io_gang_leader;
+	ASSERTV(zio_t *gio = zio->io_gang_leader);
 	dva_t *cdva = zio->io_bp->blk_dva;
 	dva_t *pdva = pio->io_bp->blk_dva;
 	uint64_t asize;