sync/atomic: add typed atomic values

These implementations will inline to the lower-level primitives,
but they hide the underlying values so that all accesses are
forced to use the atomic APIs. They also allow the use of shorter
names (methods instead of functions) at call sites, making code
more readable.

Pointer[T] also avoids conversions using unsafe.Pointer at call sites.

Discussed on #47141.
See also https://research.swtch.com/gomm for background.

Fixes #50860.

Change-Id: I0b178ee0c7747fa8985f8e48cd7b01063feb7dcc
Reviewed-on: https://go-review.googlesource.com/c/go/+/381317
Reviewed-by: Michael Pratt <[email protected]>
Run-TryBot: Russ Cox <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: rsc

api/next/50860.txt

@@ -0,0 +1,40 @@
+pkg sync/atomic, method (*Bool) CompareAndSwap(bool, bool) bool #50860
+pkg sync/atomic, method (*Bool) Load() bool #50860
+pkg sync/atomic, method (*Bool) Store(bool) #50860
+pkg sync/atomic, method (*Bool) Swap(bool) bool #50860
+pkg sync/atomic, method (*Int32) Add(int32) int32 #50860
+pkg sync/atomic, method (*Int32) CompareAndSwap(int32, int32) bool #50860
+pkg sync/atomic, method (*Int32) Load() int32 #50860
+pkg sync/atomic, method (*Int32) Store(int32) #50860
+pkg sync/atomic, method (*Int32) Swap(int32) int32 #50860
+pkg sync/atomic, method (*Int64) Add(int64) int64 #50860
+pkg sync/atomic, method (*Int64) CompareAndSwap(int64, int64) bool #50860
+pkg sync/atomic, method (*Int64) Load() int64 #50860
+pkg sync/atomic, method (*Int64) Store(int64) #50860
+pkg sync/atomic, method (*Int64) Swap(int64) int64 #50860
+pkg sync/atomic, method (*Pointer[$0]) CompareAndSwap(*$0, *$0) bool #50860
+pkg sync/atomic, method (*Pointer[$0]) Load() *$0 #50860
+pkg sync/atomic, method (*Pointer[$0]) Store(*$0) #50860
+pkg sync/atomic, method (*Pointer[$0]) Swap(*$0) *$0 #50860
+pkg sync/atomic, method (*Uint32) Add(uint32) uint32 #50860
+pkg sync/atomic, method (*Uint32) CompareAndSwap(uint32, uint32) bool #50860
+pkg sync/atomic, method (*Uint32) Load() uint32 #50860
+pkg sync/atomic, method (*Uint32) Store(uint32) #50860
+pkg sync/atomic, method (*Uint32) Swap(uint32) uint32 #50860
+pkg sync/atomic, method (*Uint64) Add(uint64) uint64 #50860
+pkg sync/atomic, method (*Uint64) CompareAndSwap(uint64, uint64) bool #50860
+pkg sync/atomic, method (*Uint64) Load() uint64 #50860
+pkg sync/atomic, method (*Uint64) Store(uint64) #50860
+pkg sync/atomic, method (*Uint64) Swap(uint64) uint64 #50860
+pkg sync/atomic, method (*Uintptr) Add(uintptr) uintptr #50860
+pkg sync/atomic, method (*Uintptr) CompareAndSwap(uintptr, uintptr) bool #50860
+pkg sync/atomic, method (*Uintptr) Load() uintptr #50860
+pkg sync/atomic, method (*Uintptr) Store(uintptr) #50860
+pkg sync/atomic, method (*Uintptr) Swap(uintptr) uintptr #50860
+pkg sync/atomic, type Bool struct #50860
+pkg sync/atomic, type Int32 struct #50860
+pkg sync/atomic, type Int64 struct #50860
+pkg sync/atomic, type Pointer[$0 interface{}] struct #50860
+pkg sync/atomic, type Uint32 struct #50860
+pkg sync/atomic, type Uint64 struct #50860
+pkg sync/atomic, type Uintptr struct #50860

src/cmd/compile/internal/test/inl_test.go

@@ -180,6 +180,42 @@ func TestIntendedInlining(t *testing.T) {
 		"net": {
 			"(*UDPConn).ReadFromUDP",
 		},
+		"sync/atomic": {
+			// (*Bool).CompareAndSwap handled below.
+			"(*Bool).Load",
+			"(*Bool).Store",
+			"(*Bool).Swap",
+			"(*Int32).Add",
+			"(*Int32).CompareAndSwap",
+			"(*Int32).Load",
+			"(*Int32).Store",
+			"(*Int32).Swap",
+			"(*Int64).Add",
+			"(*Int64).CompareAndSwap",
+			"(*Int64).Load",
+			"(*Int64).Store",
+			"(*Int64).Swap",
+			"(*Uint32).Add",
+			"(*Uint32).CompareAndSwap",
+			"(*Uint32).Load",
+			"(*Uint32).Store",
+			"(*Uint32).Swap",
+			"(*Uint64).Add",
+			"(*Uint64).CompareAndSwap",
+			"(*Uint64).Load",
+			"(*Uint64).Store",
+			"(*Uint64).Swap",
+			"(*Uintptr).Add",
+			"(*Uintptr).CompareAndSwap",
+			"(*Uintptr).Load",
+			"(*Uintptr).Store",
+			"(*Uintptr).Swap",
+			// TODO(rsc): Why are these not reported as inlined?
+			// "(*Pointer[T]).CompareAndSwap",
+			// "(*Pointer[T]).Load",
+			// "(*Pointer[T]).Store",
+			// "(*Pointer[T]).Swap",
+		},
 	}
 
 	if runtime.GOARCH != "386" && runtime.GOARCH != "mips64" && runtime.GOARCH != "mips64le" && runtime.GOARCH != "riscv64" {
@@ -199,6 +235,8 @@ func TestIntendedInlining(t *testing.T) {
 	if bits.UintSize == 64 {
 		// mix is only defined on 64-bit architectures
 		want["runtime"] = append(want["runtime"], "mix")
+		// (*Bool).CompareAndSwap is just over budget on 32-bit systems (386, arm).
+		want["sync/atomic"] = append(want["sync/atomic"], "(*Bool).CompareAndSwap")
 	}
 
 	switch runtime.GOARCH {

src/cmd/compile/internal/types/size.go

@@ -167,6 +167,11 @@ func calcStructOffset(errtype *Type, t *Type, o int64, flag int) int64 {
 	if maxalign < 1 {
 		maxalign = 1
 	}
+	// Special case: sync/atomic.align64 is an empty struct we recognize
+	// as a signal that the struct it contains must be 64-bit-aligned.
+	if isStruct && t.NumFields() == 0 && t.Sym() != nil && t.Sym().Name == "align64" && isSyncAtomic(t.Sym().Pkg) {
+		maxalign = 8
+	}
 	lastzero := int64(0)
 	for _, f := range t.Fields().Slice() {
 		if f.Type == nil {
@@ -226,6 +231,10 @@ func calcStructOffset(errtype *Type, t *Type, o int64, flag int) int64 {
 	return o
 }
 
+func isSyncAtomic(p *Pkg) bool {
+	return p.Prefix == "sync/atomic" || p.Prefix == `""` && base.Ctxt.Pkgpath == "sync/atomic"
+}
+
 // CalcSize calculates and stores the size and alignment for t.
 // If CalcSizeDisabled is set, and the size/alignment
 // have not already been calculated, it calls Fatal.