internal/abi,runtime: refactor map constants into one place

Previously TryBot-tested with bucket bits = 4. Also tested locally with bucket bits = 5. This makes it much easier to change the size of map buckets, and hopefully provides pointers to all the code that in some way depends on details of map layout. Change-Id: I9f6669d1eadd02f182d0bc3f959dc5f385fa1683 Reviewed-on: https://go-review.googlesource.com/c/go/+/462115 TryBot-Result: Gopher Robot <gobot@golang.org> Run-TryBot: David Chase <drchase@google.com> Reviewed-by: Austin Clements <austin@google.com>
2025-05-31 15:40:52 +00:00 · 2023-01-13 16:12:47 -05:00
parent e2fe35363d
commit e22bd2348c
13 changed files with 195 additions and 80 deletions
--- a/src/cmd/compile/internal/reflectdata/reflect.go
+++ b/src/cmd/compile/internal/reflectdata/reflect.go
@ -7,6 +7,7 @@ package reflectdata
 import (
 	"encoding/binary"
 	"fmt"
+	"internal/abi"
 	"os"
 	"sort"
 	"strings"
@ -65,10 +66,17 @@ type typeSig struct {
 // we include only enough information to generate a correct GC
 // program for it.
 // Make sure this stays in sync with runtime/map.go.
+//
+//	A "bucket" is a "struct" {
+//	      tophash [BUCKETSIZE]uint8
+//	      keys [BUCKETSIZE]keyType
+//	      elems [BUCKETSIZE]elemType
+//	      overflow *bucket
+//	    }
 const (
-	BUCKETSIZE  = 8
-	MAXKEYSIZE  = 128
-	MAXELEMSIZE = 128
+	BUCKETSIZE  = abi.MapBucketCount
+	MAXKEYSIZE  = abi.MapMaxKeyBytes
+	MAXELEMSIZE = abi.MapMaxElemBytes
 )

 func structfieldSize() int { return 3 * types.PtrSize }       // Sizeof(runtime.structfield{})
--- a/src/cmd/dist/buildtool.go
+++ b/src/cmd/dist/buildtool.go
@ -60,8 +60,10 @@ var bootstrapDirs = []string{
 	"debug/macho",
 	"debug/pe",
 	"go/constant",
+	"internal/abi",
 	"internal/coverage",
 	"internal/buildcfg",
+	"internal/goarch",
 	"internal/goexperiment",
 	"internal/goroot",
 	"internal/goversion",
--- a/src/cmd/link/internal/ld/dwarf.go
+++ b/src/cmd/link/internal/ld/dwarf.go
@ -22,6 +22,7 @@ import (
 	"cmd/link/internal/loader"
 	"cmd/link/internal/sym"
 	"fmt"
+	"internal/abi"
 	"internal/buildcfg"
 	"log"
 	"path"
@ -855,9 +856,9 @@ func mkinternaltypename(base string, arg1 string, arg2 string) string {

 // synthesizemaptypes is way too closely married to runtime/hashmap.c
 const (
-	MaxKeySize = 128
-	MaxValSize = 128
-	BucketSize = 8
+	MaxKeySize = abi.MapMaxKeyBytes
+	MaxValSize = abi.MapMaxElemBytes
+	BucketSize = abi.MapBucketCount
 )

 func (d *dwctxt) mkinternaltype(ctxt *Link, abbrev int, typename, keyname, valname string, f func(*dwarf.DWDie)) loader.Sym {
--- a/src/internal/abi/abi.go
+++ b/src/internal/abi/abi.go
@ -100,27 +100,3 @@ func (b *IntArgRegBitmap) Set(i int) {
 func (b *IntArgRegBitmap) Get(i int) bool {
 	return b[i/8]&(uint8(1)<<(i%8)) != 0
 }
-
-// FuncPC* intrinsics.
-//
-// CAREFUL: In programs with plugins, FuncPC* can return different values
-// for the same function (because there are actually multiple copies of
-// the same function in the address space). To be safe, don't use the
-// results of this function in any == expression. It is only safe to
-// use the result as an address at which to start executing code.
-
-// FuncPCABI0 returns the entry PC of the function f, which must be a
-// direct reference of a function defined as ABI0. Otherwise it is a
-// compile-time error.
-//
-// Implemented as a compile intrinsic.
-func FuncPCABI0(f any) uintptr
-
-// FuncPCABIInternal returns the entry PC of the function f. If f is a
-// direct reference of a function, it must be defined as ABIInternal.
-// Otherwise it is a compile-time error. If f is not a direct reference
-// of a defined function, it assumes that f is a func value. Otherwise
-// the behavior is undefined.
-//
-// Implemented as a compile intrinsic.
-func FuncPCABIInternal(f any) uintptr
--- a/src/internal/abi/funcpc.go
+++ b/src/internal/abi/funcpc.go
@ -0,0 +1,35 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !compiler_bootstrap
+// +build !compiler_bootstrap
+
+package abi
+
+// The bootstrapping compiler doesn't understand "any" in the function signatures,
+// and also does not implement these intrinsics.
+
+// FuncPC* intrinsics.
+//
+// CAREFUL: In programs with plugins, FuncPC* can return different values
+// for the same function (because there are actually multiple copies of
+// the same function in the address space). To be safe, don't use the
+// results of this function in any == expression. It is only safe to
+// use the result as an address at which to start executing code.
+
+// FuncPCABI0 returns the entry PC of the function f, which must be a
+// direct reference of a function defined as ABI0. Otherwise it is a
+// compile-time error.
+//
+// Implemented as a compile intrinsic.
+func FuncPCABI0(f any) uintptr
+
+// FuncPCABIInternal returns the entry PC of the function f. If f is a
+// direct reference of a function, it must be defined as ABIInternal.
+// Otherwise it is a compile-time error. If f is not a direct reference
+// of a defined function, it assumes that f is a func value. Otherwise
+// the behavior is undefined.
+//
+// Implemented as a compile intrinsic.
+func FuncPCABIInternal(f any) uintptr
--- a/src/internal/abi/map.go
+++ b/src/internal/abi/map.go
@ -0,0 +1,14 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package abi
+
+// Map constants common to several packages
+// runtime/runtime-gdb.py:MapTypePrinter contains its own copy
+const (
+	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.
+)
--- a/src/reflect/all_test.go
+++ b/src/reflect/all_test.go
@ -10,6 +10,7 @@ import (
 	"flag"
 	"fmt"
 	"go/token"
+	"internal/abi"
 	"internal/goarch"
 	"internal/testenv"
 	"io"
@ -31,6 +32,8 @@ import (
 	"unsafe"
 )

+const bucketCount = abi.MapBucketCount
+
 var sink any

 func TestBool(t *testing.T) {
@ -7162,7 +7165,7 @@ func TestGCBits(t *testing.T) {
 	verifyGCBits(t, TypeOf(([][10000]Xscalar)(nil)), lit(1))
 	verifyGCBits(t, SliceOf(ArrayOf(10000, Tscalar)), lit(1))

-	hdr := make([]byte, 8/goarch.PtrSize)
+	hdr := make([]byte, bucketCount/goarch.PtrSize)

 	verifyMapBucket := func(t *testing.T, k, e Type, m any, want []byte) {
 		verifyGCBits(t, MapBucketOf(k, e), want)
@ -7171,14 +7174,14 @@ func TestGCBits(t *testing.T) {
 	verifyMapBucket(t,
 		Tscalar, Tptr,
 		map[Xscalar]Xptr(nil),
-		join(hdr, rep(8, lit(0)), rep(8, lit(1)), lit(1)))
+		join(hdr, rep(bucketCount, lit(0)), rep(bucketCount, lit(1)), lit(1)))
 	verifyMapBucket(t,
 		Tscalarptr, Tptr,
 		map[Xscalarptr]Xptr(nil),
-		join(hdr, rep(8, lit(0, 1)), rep(8, lit(1)), lit(1)))
+		join(hdr, rep(bucketCount, lit(0, 1)), rep(bucketCount, lit(1)), lit(1)))
 	verifyMapBucket(t, Tint64, Tptr,
 		map[int64]Xptr(nil),
-		join(hdr, rep(8, rep(8/goarch.PtrSize, lit(0))), rep(8, lit(1)), lit(1)))
+		join(hdr, rep(bucketCount, rep(8/goarch.PtrSize, lit(0))), rep(bucketCount, lit(1)), lit(1)))
 	verifyMapBucket(t,
 		Tscalar, Tscalar,
 		map[Xscalar]Xscalar(nil),
@ -7186,23 +7189,23 @@ func TestGCBits(t *testing.T) {
 	verifyMapBucket(t,
 		ArrayOf(2, Tscalarptr), ArrayOf(3, Tptrscalar),
 		map[[2]Xscalarptr][3]Xptrscalar(nil),
-		join(hdr, rep(8*2, lit(0, 1)), rep(8*3, lit(1, 0)), lit(1)))
+		join(hdr, rep(bucketCount*2, lit(0, 1)), rep(bucketCount*3, lit(1, 0)), lit(1)))
 	verifyMapBucket(t,
 		ArrayOf(64/goarch.PtrSize, Tscalarptr), ArrayOf(64/goarch.PtrSize, Tptrscalar),
 		map[[64 / goarch.PtrSize]Xscalarptr][64 / goarch.PtrSize]Xptrscalar(nil),
-		join(hdr, rep(8*64/goarch.PtrSize, lit(0, 1)), rep(8*64/goarch.PtrSize, lit(1, 0)), lit(1)))
+		join(hdr, rep(bucketCount*64/goarch.PtrSize, lit(0, 1)), rep(bucketCount*64/goarch.PtrSize, lit(1, 0)), lit(1)))
 	verifyMapBucket(t,
 		ArrayOf(64/goarch.PtrSize+1, Tscalarptr), ArrayOf(64/goarch.PtrSize, Tptrscalar),
 		map[[64/goarch.PtrSize + 1]Xscalarptr][64 / goarch.PtrSize]Xptrscalar(nil),
-		join(hdr, rep(8, lit(1)), rep(8*64/goarch.PtrSize, lit(1, 0)), lit(1)))
+		join(hdr, rep(bucketCount, lit(1)), rep(bucketCount*64/goarch.PtrSize, lit(1, 0)), lit(1)))
 	verifyMapBucket(t,
 		ArrayOf(64/goarch.PtrSize, Tscalarptr), ArrayOf(64/goarch.PtrSize+1, Tptrscalar),
 		map[[64 / goarch.PtrSize]Xscalarptr][64/goarch.PtrSize + 1]Xptrscalar(nil),
-		join(hdr, rep(8*64/goarch.PtrSize, lit(0, 1)), rep(8, lit(1)), lit(1)))
+		join(hdr, rep(bucketCount*64/goarch.PtrSize, lit(0, 1)), rep(bucketCount, lit(1)), lit(1)))
 	verifyMapBucket(t,
 		ArrayOf(64/goarch.PtrSize+1, Tscalarptr), ArrayOf(64/goarch.PtrSize+1, Tptrscalar),
 		map[[64/goarch.PtrSize + 1]Xscalarptr][64/goarch.PtrSize + 1]Xptrscalar(nil),
-		join(hdr, rep(8, lit(1)), rep(8, lit(1)), lit(1)))
+		join(hdr, rep(bucketCount, lit(1)), rep(bucketCount, lit(1)), lit(1)))
 }

 func rep(n int, b []byte) []byte { return bytes.Repeat(b, n) }
--- a/src/reflect/type.go
+++ b/src/reflect/type.go
@ -16,6 +16,7 @@
 package reflect

 import (
+	"internal/abi"
 	"internal/goarch"
 	"strconv"
 	"sync"
@ -2226,9 +2227,9 @@ func hashMightPanic(t *rtype) bool {
 // Currently, that's just size and the GC program. We also fill in string
 // for possible debugging use.
 const (
-	bucketSize uintptr = 8
-	maxKeySize uintptr = 128
-	maxValSize uintptr = 128
+	bucketSize uintptr = abi.MapBucketCount
+	maxKeySize uintptr = abi.MapMaxKeyBytes
+	maxValSize uintptr = abi.MapMaxElemBytes
 )

 func bucketOf(ktyp, etyp *rtype) *rtype {
--- a/src/runtime/map.go
+++ b/src/runtime/map.go
@ -63,20 +63,21 @@ import (

 const (
 	// Maximum number of key/elem pairs a bucket can hold.
-	bucketCntBits = 3
-	bucketCnt     = 1 << bucketCntBits
+	bucketCntBits = abi.MapBucketCountBits
+	bucketCnt     = abi.MapBucketCount

-	// Maximum average load of a bucket that triggers growth is 6.5.
+	// Maximum average load of a bucket that triggers growth is bucketCnt*13/16 (about 80% full)
+	// Because of minimum alignment rules, bucketCnt is known to be at least 8.
 	// Represent as loadFactorNum/loadFactorDen, to allow integer math.
-	loadFactorNum = 13
 	loadFactorDen = 2
+	loadFactorNum = (bucketCnt * 13 / 16) * loadFactorDen

 	// Maximum key or elem size to keep inline (instead of mallocing per element).
 	// Must fit in a uint8.
 	// Fast versions cannot handle big elems - the cutoff size for
 	// fast versions in cmd/compile/internal/gc/walk.go must be at most this elem.
-	maxKeySize  = 128
-	maxElemSize = 128
+	maxKeySize  = abi.MapMaxKeyBytes
+	maxElemSize = abi.MapMaxElemBytes

 	// data offset should be the size of the bmap struct, but needs to be
 	// aligned correctly. For amd64p32 this means 64-bit alignment
--- a/src/runtime/map_test.go
+++ b/src/runtime/map_test.go
@ -6,6 +6,7 @@ package runtime_test

 import (
 	"fmt"
+	"internal/abi"
 	"internal/goarch"
 	"math"
 	"reflect"
@ -506,7 +507,12 @@ func TestMapNanGrowIterator(t *testing.T) {
 }

 func TestMapIterOrder(t *testing.T) {
-	for _, n := range [...]int{3, 7, 9, 15} {
+	sizes := []int{3, 7, 9, 15}
+	if abi.MapBucketCountBits >= 5 {
+		// it gets flaky (often only one iteration order) at size 3 when abi.MapBucketCountBits >=5.
+		t.Fatalf("This test becomes flaky if abi.MapBucketCountBits(=%d) is 5 or larger", abi.MapBucketCountBits)
+	}
+	for _, n := range sizes {
 		for i := 0; i < 1000; i++ {
 			// Make m be {0: true, 1: true, ..., n-1: true}.
 			m := make(map[int]bool)
@ -673,6 +679,17 @@ func TestIgnoreBogusMapHint(t *testing.T) {
 	}
 }

+const bs = abi.MapBucketCount
+
+// belowOverflow should be a pretty-full pair of buckets;
+// atOverflow is 1/8 bs larger = 13/8 buckets or two buckets
+// that are 13/16 full each, which is the overflow boundary.
+// Adding one to that should ensure overflow to the next higher size.
+const (
+	belowOverflow = bs * 3 / 2           // 1.5 bs = 2 buckets @ 75%
+	atOverflow    = belowOverflow + bs/8 // 2 buckets at 13/16 fill.
+)
+
 var mapBucketTests = [...]struct {
 	n        int // n is the number of map elements
 	noescape int // number of expected buckets for non-escaping map
@ -682,11 +699,16 @@ var mapBucketTests = [...]struct {
 	{-1, 1, 1},
 	{0, 1, 1},
 	{1, 1, 1},
-	{8, 1, 1},
-	{9, 2, 2},
-	{13, 2, 2},
-	{14, 4, 4},
-	{26, 4, 4},
+	{bs, 1, 1},
+	{bs + 1, 2, 2},
+	{belowOverflow, 2, 2},  // 1.5 bs = 2 buckets @ 75%
+	{atOverflow + 1, 4, 4}, // 13/8 bs + 1 == overflow to 4
+
+	{2 * belowOverflow, 4, 4}, // 3 bs = 4 buckets @75%
+	{2*atOverflow + 1, 8, 8},  // 13/4 bs + 1 = overflow to 8
+
+	{4 * belowOverflow, 8, 8},  // 6 bs = 8 buckets @ 75%
+	{4*atOverflow + 1, 16, 16}, // 13/2 bs + 1 = overflow to 16
 }

 func TestMapBuckets(t *testing.T) {
--- a/src/runtime/runtime-gdb.py
+++ b/src/runtime/runtime-gdb.py
@ -160,6 +160,7 @@ class MapTypePrinter:
 		return str(self.val.type)

 	def children(self):
+		MapBucketCount = 8 # see internal/abi.go:MapBucketCount
 		B = self.val['B']
 		buckets = self.val['buckets']
 		oldbuckets = self.val['oldbuckets']
@ -178,7 +179,7 @@ class MapTypePrinter:
 					bp = oldbp
 			while bp:
 				b = bp.dereference()
-				for i in xrange(8):
+				for i in xrange(MapBucketCount):
 					if b['tophash'][i] != 0:
 						k = b['keys'][i]
 						v = b['values'][i]
--- a/src/runtime/runtime-gdb_test.go
+++ b/src/runtime/runtime-gdb_test.go
@ -8,6 +8,7 @@ import (
 	"bytes"
 	"flag"
 	"fmt"
+	"internal/abi"
 	"internal/testenv"
 	"os"
 	"os/exec"
@ -114,13 +115,16 @@ func checkCleanBacktrace(t *testing.T, backtrace string) {
 	// TODO(mundaym): check for unknown frames (e.g. "??").
 }

-const helloSource = `
+// NOTE: the maps below are allocated larger than abi.MapBucketCount
+// to ensure that they are not "optimized out".
+
+var helloSource = `
 import "fmt"
 import "runtime"
 var gslice []string
 func main() {
-	mapvar := make(map[string]string, 13)
-	slicemap := make(map[string][]string,11)
+	mapvar := make(map[string]string, ` + strconv.FormatInt(abi.MapBucketCount+9, 10) + `)
+	slicemap := make(map[string][]string,` + strconv.FormatInt(abi.MapBucketCount+3, 10) + `)
    chanint := make(chan int, 10)
    chanstr := make(chan string, 10)
    chanint <- 99
--- a/test/codegen/maps.go
+++ b/test/codegen/maps.go
@ -124,31 +124,78 @@ func MapClearSideEffect(m map[int]int) int {
 }

 func MapLiteralSizing(x int) (map[int]int, map[int]int) {
-	// amd64:"MOVL\t[$]10,"
+	// This is tested for internal/abi/maps.go:MapBucketCountBits={3,4,5}
+	// amd64:"MOVL\t[$]33,"
 	m := map[int]int{
-		0: 0,
-		1: 1,
-		2: 2,
-		3: 3,
-		4: 4,
-		5: 5,
-		6: 6,
-		7: 7,
-		8: 8,
-		9: 9,
+		0:  0,
+		1:  1,
+		2:  2,
+		3:  3,
+		4:  4,
+		5:  5,
+		6:  6,
+		7:  7,
+		8:  8,
+		9:  9,
+		10: 10,
+		11: 11,
+		12: 12,
+		13: 13,
+		14: 14,
+		15: 15,
+		16: 16,
+		17: 17,
+		18: 18,
+		19: 19,
+		20: 20,
+		21: 21,
+		22: 22,
+		23: 23,
+		24: 24,
+		25: 25,
+		26: 26,
+		27: 27,
+		28: 28,
+		29: 29,
+		30: 30,
+		31: 32,
+		32: 32,
 	}
-	// amd64:"MOVL\t[$]10,"
+	// amd64:"MOVL\t[$]33,"
 	n := map[int]int{
-		0: x,
-		1: x,
-		2: x,
-		3: x,
-		4: x,
-		5: x,
-		6: x,
-		7: x,
-		8: x,
-		9: x,
+		0:  0,
+		1:  1,
+		2:  2,
+		3:  3,
+		4:  4,
+		5:  5,
+		6:  6,
+		7:  7,
+		8:  8,
+		9:  9,
+		10: 10,
+		11: 11,
+		12: 12,
+		13: 13,
+		14: 14,
+		15: 15,
+		16: 16,
+		17: 17,
+		18: 18,
+		19: 19,
+		20: 20,
+		21: 21,
+		22: 22,
+		23: 23,
+		24: 24,
+		25: 25,
+		26: 26,
+		27: 27,
+		28: 28,
+		29: 29,
+		30: 30,
+		31: 32,
+		32: 32,
 	}
 	return m, n
 }