reftable/record: store "val2" hashes as static arrays

Similar to the preceding commit, convert ref records of type "val2" to
store their object IDs in static arrays instead of allocating them for
every single record.

We're using the same benchmark as in the preceding commit, with `git
show-ref --quiet` in a repository with ~350k refs. This time around
though the effects aren't this huge. Before:

    HEAP SUMMARY:
        in use at exit: 21,163 bytes in 193 blocks
      total heap usage: 1,419,040 allocs, 1,418,847 frees, 62,153,868 bytes allocated

After:

    HEAP SUMMARY:
        in use at exit: 21,163 bytes in 193 blocks
      total heap usage: 1,410,148 allocs, 1,409,955 frees, 61,976,068 bytes allocated

This is because "val2"-type records are typically only stored for peeled
tags, and the number of annotated tags in the benchmark repository is
rather low. Still, it can be seen that this change leads to a reduction
of allocations overall, even if only a small one.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

reftable/readwrite_test.c

@@ -547,8 +547,6 @@ static void test_table_refs_for(int indexed)
 		uint8_t hash[GIT_SHA1_RAWSZ];
 		char fill[51] = { 0 };
 		char name[100];
-		uint8_t hash1[GIT_SHA1_RAWSZ];
-		uint8_t hash2[GIT_SHA1_RAWSZ];
 		struct reftable_ref_record ref = { NULL };
 
 		memset(hash, i, sizeof(hash));
@@ -558,20 +556,18 @@ static void test_table_refs_for(int indexed)
 		name[40] = 0;
 		ref.refname = name;
 
-		set_test_hash(hash1, i / 4);
-		set_test_hash(hash2, 3 + i / 4);
 		ref.value_type = REFTABLE_REF_VAL2;
-		ref.value.val2.value = hash1;
-		ref.value.val2.target_value = hash2;
+		set_test_hash(ref.value.val2.value, i / 4);
+		set_test_hash(ref.value.val2.target_value, 3 + i / 4);
 
 		/* 80 bytes / entry, so 3 entries per block. Yields 17
 		 */
 		/* blocks. */
 		n = reftable_writer_add_ref(w, &ref);
 		EXPECT(n == 0);
 
-		if (!memcmp(hash1, want_hash, GIT_SHA1_RAWSZ) ||
-		    !memcmp(hash2, want_hash, GIT_SHA1_RAWSZ)) {
+		if (!memcmp(ref.value.val2.value, want_hash, GIT_SHA1_RAWSZ) ||
+		    !memcmp(ref.value.val2.target_value, want_hash, GIT_SHA1_RAWSZ)) {
 			want_names[want_names_len++] = xstrdup(name);
 		}
 	}

reftable/record.c

@@ -222,9 +222,7 @@ static void reftable_ref_record_copy_from(void *rec, const void *src_rec,
 		memcpy(ref->value.val1, src->value.val1, hash_size);
 		break;
 	case REFTABLE_REF_VAL2:
-		ref->value.val2.value = reftable_malloc(hash_size);
 		memcpy(ref->value.val2.value, src->value.val2.value, hash_size);
-		ref->value.val2.target_value = reftable_malloc(hash_size);
 		memcpy(ref->value.val2.target_value,
 		       src->value.val2.target_value, hash_size);
 		break;
@@ -298,8 +296,6 @@ void reftable_ref_record_release(struct reftable_ref_record *ref)
 		reftable_free(ref->value.symref);
 		break;
 	case REFTABLE_REF_VAL2:
-		reftable_free(ref->value.val2.target_value);
-		reftable_free(ref->value.val2.value);
 		break;
 	case REFTABLE_REF_VAL1:
 		break;
@@ -401,11 +397,9 @@ static int reftable_ref_record_decode(void *rec, struct strbuf key,
 			return -1;
 		}
 
-		r->value.val2.value = reftable_malloc(hash_size);
 		memcpy(r->value.val2.value, in.buf, hash_size);
 		string_view_consume(&in, hash_size);
 
-		r->value.val2.target_value = reftable_malloc(hash_size);
 		memcpy(r->value.val2.target_value, in.buf, hash_size);
 		string_view_consume(&in, hash_size);
 		break;

reftable/record_test.c

@@ -122,11 +122,7 @@ static void test_reftable_ref_record_roundtrip(void)
 			set_hash(in.u.ref.value.val1, 1);
 			break;
 		case REFTABLE_REF_VAL2:
-			in.u.ref.value.val2.value =
-				reftable_malloc(GIT_SHA1_RAWSZ);
 			set_hash(in.u.ref.value.val2.value, 1);
-			in.u.ref.value.val2.target_value =
-				reftable_malloc(GIT_SHA1_RAWSZ);
 			set_hash(in.u.ref.value.val2.target_value, 2);
 			break;
 		case REFTABLE_REF_SYMREF:

reftable/reftable-record.h

@@ -41,8 +41,8 @@ struct reftable_ref_record {
 	union {
 		unsigned char val1[GIT_MAX_RAWSZ];
 		struct {
-			uint8_t *value; /* first value, malloced hash  */
-			uint8_t *target_value; /* second value, malloced hash */
+			unsigned char value[GIT_MAX_RAWSZ]; /* first hash  */
+			unsigned char target_value[GIT_MAX_RAWSZ]; /* second hash */
 		} val2;
 		char *symref; /* referent, malloced 0-terminated string */
 	} value;