runtime: use MapMaxKeyBytes,MapMaxElemBytes,MapBucketCount of internal/abi

For #59670

Change-Id: I9265e033bf3a84c3dc7b4a5d52c0df9672435f0d
GitHub-Last-Rev: 8e40990
GitHub-Pull-Request: #64774
Reviewed-on: https://go-review.googlesource.com/c/go/+/550117
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: qiulaidongfeng

src/cmd/compile/internal/walk/walk.go

@@ -6,6 +6,7 @@ package walk
 
 import (
 	"fmt"
+	"internal/abi"
 
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/ir"
@@ -183,8 +184,7 @@ var mapassign = mkmapnames("mapassign", "ptr")
 var mapdelete = mkmapnames("mapdelete", "")
 
 func mapfast(t *types.Type) int {
-	// Check runtime/map.go:maxElemSize before changing.
-	if t.Elem().Size() > 128 {
+	if t.Elem().Size() > abi.MapMaxElemBytes {
 		return mapslow
 	}
 	switch reflectdata.AlgType(t.Key()) {

src/internal/abi/map.go

@@ -7,10 +7,15 @@ package abi
 // Map constants common to several packages
 // runtime/runtime-gdb.py:MapTypePrinter contains its own copy
 const (
+	// Maximum number of key/elem pairs a bucket can hold.
 	MapBucketCountBits = 3 // log2 of number of elements in a bucket.
 	MapBucketCount     = 1 << MapBucketCountBits
-	MapMaxKeyBytes     = 128 // Must fit in a uint8.
-	MapMaxElemBytes    = 128 // Must fit in a uint8.
+
+	// Maximum key or elem size to keep inline (instead of mallocing per element).
+	// Must fit in a uint8.
+	// Note: fast map functions cannot handle big elems (bigger than MapMaxElemBytes).
+	MapMaxKeyBytes  = 128
+	MapMaxElemBytes = 128 // Must fit in a uint8.
 )
 
 // ZeroValSize is the size in bytes of runtime.zeroVal.

src/runtime/export_test.go

@@ -751,15 +751,15 @@ func MapTombstoneCheck(m map[int]int) {
 		b0 := (*bmap)(add(h.buckets, uintptr(x)*uintptr(t.BucketSize)))
 		n := 0
 		for b := b0; b != nil; b = b.overflow(t) {
-			for i := 0; i < bucketCnt; i++ {
+			for i := 0; i < abi.MapBucketCount; i++ {
 				if b.tophash[i] != emptyRest {
 					n++
 				}
 			}
 		}
 		k := 0
 		for b := b0; b != nil; b = b.overflow(t) {
-			for i := 0; i < bucketCnt; i++ {
+			for i := 0; i < abi.MapBucketCount; i++ {
 				if k < n && b.tophash[i] == emptyRest {
 					panic("early emptyRest")
 				}