internal/runtime/maps: assume constant elem offset with int64 and string keys

Note this doesn't work with int32 keys because alignment padding can change
the offset of the element.

Change-Id: I27804d3cfc7cc1b7f995f7e29630f0824f0ee899
Reviewed-on: https://go-review.googlesource.com/c/go/+/629418
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>

diff --git a/src/cmd/compile/internal/reflectdata/map_swiss.go b/src/cmd/compile/internal/reflectdata/map_swiss.go
index 86c07ef117ee633b5c6d02a85284da49df9f6869..074c36a453339a57fb6da4de9e702e27ec1dd1ff 100644 (file)
--- a/src/cmd/compile/internal/reflectdata/map_swiss.go
+++ b/src/cmd/compile/internal/reflectdata/map_swiss.go
@@ -269,6 +269,12 @@ func writeSwissMapType(t *types.Type, lsym *obj.LSym, c rttype.Cursor) {
 
        slotTyp := gtyp.Field(1).Type.Elem()
        elemOff := slotTyp.Field(1).Offset
+       if AlgType(t.Key()) == types.AMEM64 && elemOff != 8 {
+               base.Fatalf("runtime assumes elemOff for 8-byte keys is 8, got %d", elemOff)
+       }
+       if AlgType(t.Key()) == types.ASTRING && elemOff != int64(2*types.PtrSize) {
+               base.Fatalf("runtime assumes elemOff for string keys is %d, got %d", 2*types.PtrSize, elemOff)
+       }
 
        c.Field("Key").WritePtr(s1)
        c.Field("Elem").WritePtr(s2)

diff --git a/src/internal/runtime/maps/runtime_fast64_swiss.go b/src/internal/runtime/maps/runtime_fast64_swiss.go
index f4716dffdaaf8874754f13788b94625c2d271346..90e84f83d2539ab23bfce1c2b575724e9fc31b19 100644 (file)
--- a/src/internal/runtime/maps/runtime_fast64_swiss.go
+++ b/src/internal/runtime/maps/runtime_fast64_swiss.go
@@ -39,7 +39,7 @@ func runtime_mapaccess1_fast64(typ *abi.SwissMapType, m *Map, key uint64) unsafe
                slotSize := typ.SlotSize
                for full != 0 {
                        if key == *(*uint64)(slotKey) && full&(1<<7) != 0 {
-                               slotElem := unsafe.Pointer(uintptr(slotKey) + typ.ElemOff)
+                               slotElem := unsafe.Pointer(uintptr(slotKey) + 8)
                                return slotElem
                        }
                        slotKey = unsafe.Pointer(uintptr(slotKey) + slotSize)
@@ -66,7 +66,7 @@ func runtime_mapaccess1_fast64(typ *abi.SwissMapType, m *Map, key uint64) unsafe
 
                        slotKey := g.key(typ, i)
                        if key == *(*uint64)(slotKey) {
-                               slotElem := unsafe.Pointer(uintptr(slotKey) + typ.ElemOff)
+                               slotElem := unsafe.Pointer(uintptr(slotKey) + 8)
                                return slotElem
                        }
                        match = match.removeFirst()
@@ -107,7 +107,7 @@ func runtime_mapaccess2_fast64(typ *abi.SwissMapType, m *Map, key uint64) (unsaf
                slotSize := typ.SlotSize
                for full != 0 {
                        if key == *(*uint64)(slotKey) && full&(1<<7) != 0 {
-                               slotElem := unsafe.Pointer(uintptr(slotKey) + typ.ElemOff)
+                               slotElem := unsafe.Pointer(uintptr(slotKey) + 8)
                                return slotElem, true
                        }
                        slotKey = unsafe.Pointer(uintptr(slotKey) + slotSize)
@@ -134,7 +134,7 @@ func runtime_mapaccess2_fast64(typ *abi.SwissMapType, m *Map, key uint64) (unsaf
 
                        slotKey := g.key(typ, i)
                        if key == *(*uint64)(slotKey) {
-                               slotElem := unsafe.Pointer(uintptr(slotKey) + typ.ElemOff)
+                               slotElem := unsafe.Pointer(uintptr(slotKey) + 8)
                                return slotElem, true
                        }
                        match = match.removeFirst()

diff --git a/src/internal/runtime/maps/runtime_faststr_swiss.go b/src/internal/runtime/maps/runtime_faststr_swiss.go
index eed8d8666d4ebe125af603cf8f3e0524a367f162..a104945501d3745ff8fd95f7ae15a387b146af46 100644 (file)
--- a/src/internal/runtime/maps/runtime_faststr_swiss.go
+++ b/src/internal/runtime/maps/runtime_faststr_swiss.go
@@ -8,6 +8,7 @@ package maps
 
 import (
        "internal/abi"
+       "internal/goarch"
        "internal/race"
        "internal/runtime/sys"
        "unsafe"
@@ -48,7 +49,7 @@ func (m *Map) getWithoutKeySmallFastStr(typ *abi.SwissMapType, key string) unsaf
                // There's exactly one slot that passed the quick test. Do the single expensive comparison.
                slotKey = g.key(typ, uintptr(j))
                if key == *(*string)(slotKey) {
-                       return unsafe.Pointer(uintptr(slotKey) + typ.ElemOff)
+                       return unsafe.Pointer(uintptr(slotKey) + 2*goarch.PtrSize)
                }
                return nil
        }
@@ -62,7 +63,7 @@ dohash:
 
        for range abi.SwissMapGroupSlots {
                if uint8(ctrls) == h2 && key == *(*string)(slotKey) {
-                       return unsafe.Pointer(uintptr(slotKey) + typ.ElemOff)
+                       return unsafe.Pointer(uintptr(slotKey) + 2*goarch.PtrSize)
                }
                slotKey = unsafe.Pointer(uintptr(slotKey) + slotSize)
                ctrls >>= 8
@@ -141,7 +142,7 @@ func runtime_mapaccess1_faststr(typ *abi.SwissMapType, m *Map, key string) unsaf
 
                        slotKey := g.key(typ, i)
                        if key == *(*string)(slotKey) {
-                               slotElem := unsafe.Pointer(uintptr(slotKey) + typ.ElemOff)
+                               slotElem := unsafe.Pointer(uintptr(slotKey) + 2*goarch.PtrSize)
                                return slotElem
                        }
                        match = match.removeFirst()
@@ -199,7 +200,7 @@ func runtime_mapaccess2_faststr(typ *abi.SwissMapType, m *Map, key string) (unsa
 
                        slotKey := g.key(typ, i)
                        if key == *(*string)(slotKey) {
-                               slotElem := unsafe.Pointer(uintptr(slotKey) + typ.ElemOff)
+                               slotElem := unsafe.Pointer(uintptr(slotKey) + 2*goarch.PtrSize)
                                return slotElem, true
                        }
                        match = match.removeFirst()