MDEV-30567 rec_get_offsets() is not optimal

rec_init_offsets_comp_ordinary(), rec_init_offsets(),
rec_get_offsets_reverse(), rec_get_nth_field_offs_old():
Simplify some bitwise arithmetics to avoid conditional jumps,
and add branch prediction hints with the assumption that most
variable-length columns are short.

Tested by: Matthias Leich

storage/innobase/rem/rem0rec.cc

@@ -217,14 +217,12 @@ rec_get_n_extern_new(
 			stored in one byte for 0..127.  The length
 			will be encoded in two bytes when it is 128 or
 			more, or when the field is stored externally. */
-			if (DATA_BIG_COL(col)) {
-				if (len & 0x80) {
-					/* 1exxxxxxx xxxxxxxx */
-					if (len & 0x40) {
-						n_extern++;
-					}
-					lens--;
+			if (UNIV_UNLIKELY(len & 0x80) && DATA_BIG_COL(col)) {
+				/* 1exxxxxxx xxxxxxxx */
+				if (len & 0x40) {
+					n_extern++;
 				}
+				lens--;
 			}
 		}
 	} while (++i < n);
@@ -432,24 +430,21 @@ rec_init_offsets_comp_ordinary(
 			stored in one byte for 0..127.  The length
 			will be encoded in two bytes when it is 128 or
 			more, or when the field is stored externally. */
-			if ((len & 0x80) && DATA_BIG_COL(col)) {
+			if (UNIV_UNLIKELY(len & 0x80) && DATA_BIG_COL(col)) {
 				/* 1exxxxxxx xxxxxxxx */
 				len <<= 8;
 				len |= *lens--;
-
+				static_assert(STORED_OFFPAGE == 0x4000, "");
+				static_assert(REC_OFFS_EXTERNAL == 0x4000, "");
+				const rec_offs ext = len & REC_OFFS_EXTERNAL;
 				offs += get_value(len);
-				if (UNIV_UNLIKELY(len & 0x4000)) {
-					ut_ad(dict_index_is_clust(index));
-					any |= REC_OFFS_EXTERNAL;
-					len = combine(offs, STORED_OFFPAGE);
-				} else {
-					len = offs;
-				}
-
+				len = offs | ext;
+				any |= ext;
+				ut_ad(!ext || index->is_primary());
 				continue;
 			}
 
-			len = offs += len;
+			len = offs += static_cast<rec_offs>(len);
 		} else {
 			len = offs += field->fixed_len;
 		}
@@ -714,23 +709,20 @@ rec_init_offsets(
 				encoded in two bytes when it is 128 or
 				more, or when the field is stored
 				externally. */
-				if (DATA_BIG_COL(col)) {
-					if (len & 0x80) {
-						/* 1exxxxxxx xxxxxxxx */
-
-						len <<= 8;
-						len |= *lens--;
-
-						/* B-tree node pointers
-						must not contain externally
-						stored columns.  Thus
-						the "e" flag must be 0. */
-						ut_a(!(len & 0x4000));
-						offs += get_value(len);
-						len = offs;
-
-						goto resolved;
-					}
+				if (UNIV_UNLIKELY(len & 0x80)
+				    && DATA_BIG_COL(col)) {
+					/* 1exxxxxxx xxxxxxxx */
+					len <<= 8;
+					len |= *lens--;
+
+					/* B-tree node pointers
+					must not contain externally
+					stored columns.	 Thus
+					the "e" flag must be 0. */
+					ut_a(!(len & 0x4000));
+					offs += len & 0x3fff;
+					len = offs;
+					goto resolved;
 				}
 
 				len = offs += len;
@@ -758,26 +750,24 @@ rec_init_offsets(
 			do {
 				offs = rec_1_get_field_end_info(rec, i);
 				if (offs & REC_1BYTE_SQL_NULL_MASK) {
-					offs &= ~REC_1BYTE_SQL_NULL_MASK;
-					set_type(offs, SQL_NULL);
+					offs ^= REC_1BYTE_SQL_NULL_MASK
+						| SQL_NULL;
 				}
 				rec_offs_base(offsets)[1 + i] = offs;
 			} while (++i < n);
 		} else {
-			offs += 2 * static_cast<rec_offs>(n_fields);
+			offs += static_cast<rec_offs>(2 * n_fields);
 			any = offs;
 			/* Determine offsets to fields */
 			do {
 				offs = rec_2_get_field_end_info(rec, i);
-				if (offs & REC_2BYTE_SQL_NULL_MASK) {
-					offs &= ~REC_2BYTE_SQL_NULL_MASK;
-					set_type(offs, SQL_NULL);
-				}
-				if (offs & REC_2BYTE_EXTERN_MASK) {
-					offs &= ~REC_2BYTE_EXTERN_MASK;
-					set_type(offs, STORED_OFFPAGE);
-					any |= REC_OFFS_EXTERNAL;
-				}
+				static_assert(REC_2BYTE_SQL_NULL_MASK
+					      == SQL_NULL, "");
+				static_assert(REC_2BYTE_EXTERN_MASK
+					      == STORED_OFFPAGE, "");
+				static_assert(REC_OFFS_EXTERNAL
+					      == STORED_OFFPAGE, "");
+				any |= (offs & REC_OFFS_EXTERNAL);
 				rec_offs_base(offsets)[1 + i] = offs;
 			} while (++i < n);
 		}
@@ -1028,23 +1018,18 @@ rec_get_offsets_reverse(
 			stored in one byte for 0..127.  The length
 			will be encoded in two bytes when it is 128 or
 			more, or when the field is stored externally. */
-			if (DATA_BIG_COL(col)) {
-				if (len & 0x80) {
-					/* 1exxxxxxx xxxxxxxx */
-					len <<= 8;
-					len |= *lens++;
-
-					offs += get_value(len);
-					if (UNIV_UNLIKELY(len & 0x4000)) {
-						any_ext = REC_OFFS_EXTERNAL;
-						len = combine(offs,
-							      STORED_OFFPAGE);
-					} else {
-						len = offs;
-					}
-
-					goto resolved;
-				}
+			if (UNIV_UNLIKELY(len & 0x80) && DATA_BIG_COL(col)) {
+				/* 1exxxxxxx xxxxxxxx */
+				len &= 0x7f;
+				len <<= 8;
+				len |= *lens++;
+				static_assert(STORED_OFFPAGE == 0x4000, "");
+				static_assert(REC_OFFS_EXTERNAL == 0x4000, "");
+				rec_offs ext = len & REC_OFFS_EXTERNAL;
+				offs += get_value(len);
+				len = offs | ext;
+				any_ext |= ext;
+				goto resolved;
 			}
 
 			len = offs += len;
@@ -1089,7 +1074,7 @@ rec_get_nth_field_offs_old(
 			return(os);
 		}
 
-		next_os = next_os & ~REC_1BYTE_SQL_NULL_MASK;
+		next_os &= ~REC_1BYTE_SQL_NULL_MASK;
 	} else {
 		os = rec_2_get_field_start_offs(rec, n);
 
@@ -1101,8 +1086,7 @@ rec_get_nth_field_offs_old(
 			return(os);
 		}
 
-		next_os = next_os & ~(REC_2BYTE_SQL_NULL_MASK
-				      | REC_2BYTE_EXTERN_MASK);
+		next_os &= ~(REC_2BYTE_SQL_NULL_MASK | REC_2BYTE_EXTERN_MASK);
 	}
 
 	*len = next_os - os;
@@ -1255,7 +1239,8 @@ rec_get_converted_size_comp_prefix_low(
 		} else if (dfield_is_ext(dfield)) {
 			ut_ad(DATA_BIG_COL(field->col));
 			extra_size += 2;
-		} else if (len < 128 || !DATA_BIG_COL(field->col)) {
+		} else if (UNIV_LIKELY(len < 128)
+			   || !DATA_BIG_COL(field->col)) {
 			extra_size++;
 		} else {
 			/* For variable-length columns, we look up the
@@ -1652,7 +1637,7 @@ rec_convert_dtuple_to_rec_comp(
 
 			/* set the null flag if necessary */
 			if (dfield_is_null(field)) {
-				*nulls |= null_mask;
+				*nulls |= static_cast<byte>(null_mask);
 				null_mask <<= 1;
 				continue;
 			}
@@ -2122,14 +2107,12 @@ rec_copy_prefix_to_buf(
 			stored in one byte for 0..127.  The length
 			will be encoded in two bytes when it is 128 or
 			more, or when the column is stored externally. */
-			if (DATA_BIG_COL(col)) {
-				if (len & 0x80) {
-					/* 1exxxxxx */
-					len &= 0x3f;
-					len <<= 8;
-					len |= *lens--;
-					UNIV_PREFETCH_R(lens);
-				}
+			if (UNIV_UNLIKELY(len & 0x80) && DATA_BIG_COL(col)) {
+				/* 1exxxxxx */
+				len &= 0x3f;
+				len <<= 8;
+				len |= *lens--;
+				UNIV_PREFETCH_R(lens);
 			}
 			prefix_len += len;
 		}