From: Keith Randall <khr@golang.org>
Date: Mon, 4 Nov 2024 23:52:02 +0000 (-0800)
Subject: runtime/internal/maps: remove entryMask
X-Git-Tag: go1.24rc1~350
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=01e1e5c20438145df65a2fb79c77e3d5c3eb6831;p=gostls13.git

runtime/internal/maps: remove entryMask

It is easily recomputed as capacity-1.

This reduces a table from 40 to 32 bytes (on 64-bit archs).
That gets us down one sizeclass.

Change-Id: Icb74fb2de50baa18ca62052c7b2fe8e6af4c8837
Reviewed-on: https://go-review.googlesource.com/c/go/+/625198
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Keith Randall <khr@google.com>
---

diff --git a/src/cmd/compile/internal/reflectdata/map_swiss.go b/src/cmd/compile/internal/reflectdata/map_swiss.go
index 629136821b..86c07ef117 100644
--- a/src/cmd/compile/internal/reflectdata/map_swiss.go
+++ b/src/cmd/compile/internal/reflectdata/map_swiss.go
@@ -109,7 +109,6 @@ func swissTableType() *types.Type {
 	//     // From groups.
 	//     groups_data       unsafe.Pointer
 	//     groups_lengthMask uint64
-	//     groups_entryMask  uint64
 	// }
 	// must match internal/runtime/maps/table.go:table.
 	fields := []*types.Field{
@@ -120,7 +119,6 @@ func swissTableType() *types.Type {
 		makefield("index", types.Types[types.TINT]),
 		makefield("groups_data", types.Types[types.TUNSAFEPTR]),
 		makefield("groups_lengthMask", types.Types[types.TUINT64]),
-		makefield("groups_entryMask", types.Types[types.TUINT64]),
 	}
 
 	n := ir.NewDeclNameAt(src.NoXPos, ir.OTYPE, ir.Pkgs.InternalMaps.Lookup("table"))
@@ -131,9 +129,9 @@ func swissTableType() *types.Type {
 	table.SetUnderlying(types.NewStruct(fields))
 	types.CalcSize(table)
 
-	// The size of table should be 40 bytes on 64 bit
-	// and 32 bytes on 32 bit platforms.
-	if size := int64(3*2 + 2*1 /* one extra for padding */ + 2*8 + 2*types.PtrSize); table.Size() != size {
+	// The size of table should be 32 bytes on 64 bit
+	// and 24 bytes on 32 bit platforms.
+	if size := int64(3*2 + 2*1 /* one extra for padding */ + 1*8 + 2*types.PtrSize); table.Size() != size {
 		base.Fatalf("internal/runtime/maps.table size not correct: got %d, want %d", table.Size(), size)
 	}
 
diff --git a/src/internal/runtime/maps/group.go b/src/internal/runtime/maps/group.go
index aae667c8d8..59df1fb25a 100644
--- a/src/internal/runtime/maps/group.go
+++ b/src/internal/runtime/maps/group.go
@@ -218,9 +218,6 @@ type groupsReference struct {
 	// length must be a power of two). This allows computing i%length
 	// quickly using bitwise AND.
 	lengthMask uint64
-
-	// entryMask is the total number of slots in the groups minus one.
-	entryMask uint64
 }
 
 // newGroups allocates a new array of length groups.
@@ -231,7 +228,6 @@ func newGroups(typ *abi.SwissMapType, length uint64) groupsReference {
 		// TODO: make the length type the same throughout.
 		data:       newarray(typ.Group, int(length)),
 		lengthMask: length - 1,
-		entryMask:  (length * abi.SwissMapGroupSlots) - 1,
 	}
 }
 
diff --git a/src/internal/runtime/maps/table.go b/src/internal/runtime/maps/table.go
index 847ff7fa6b..80745e9a72 100644
--- a/src/internal/runtime/maps/table.go
+++ b/src/internal/runtime/maps/table.go
@@ -803,7 +803,8 @@ func (it *Iter) Next() {
 		// table for key selection if the table has grown. See comment
 		// on grown below.
 
-		if it.entryIdx > it.tab.groups.entryMask {
+		entryMask := uint64(it.tab.capacity) - 1
+		if it.entryIdx > entryMask {
 			// Continue to next table.
 			continue
 		}
@@ -819,7 +820,7 @@ func (it *Iter) Next() {
 		// it is cheaper to check a single slot than do a full control
 		// match.
 
-		entryIdx := (it.entryIdx + it.entryOffset) & it.tab.groups.entryMask
+		entryIdx := (it.entryIdx + it.entryOffset) & entryMask
 		slotIdx := uintptr(entryIdx & (abi.SwissMapGroupSlots - 1))
 		if slotIdx == 0 || it.group.data == nil {
 			// Only compute the group (a) when we switch
@@ -864,7 +865,7 @@ func (it *Iter) Next() {
 			return
 		}
 
-next:
+	next:
 		it.entryIdx++
 
 		// Slow path: use a match on the control word to jump ahead to
@@ -885,8 +886,8 @@ next:
 		// double-check the control value.
 
 		var groupMatch bitset
-		for it.entryIdx <= it.tab.groups.entryMask {
-			entryIdx := (it.entryIdx + it.entryOffset) & it.tab.groups.entryMask
+		for it.entryIdx <= entryMask {
+			entryIdx := (it.entryIdx + it.entryOffset) & entryMask
 			slotIdx := uintptr(entryIdx & (abi.SwissMapGroupSlots - 1))
 
 			if slotIdx == 0 || it.group.data == nil {
@@ -918,7 +919,7 @@ next:
 
 				i := groupMatch.first()
 				it.entryIdx += uint64(i - slotIdx)
-				if it.entryIdx > it.tab.groups.entryMask {
+				if it.entryIdx > entryMask {
 					// Past the end of this table's iteration.
 					continue
 				}