cmd/go,cmd/compile,sync: remove special import case in cmd/go

CL 253748 introduced a special case in cmd/go to allow sync to import
runtime/internal/atomic. Besides introducing unnecessary complexity
into cmd/go, this breaks other packages (like gopls) that understand
how imports work, but don't understand this special case.

Fix this by using the more standard linkname-based approach to pull
the necessary functions from runtime/internal/atomic into sync. Since
these are compiler intrinsics, we also have to tell the compiler that
the linknamed symbols are intrinsics to get this optimization in sync.

Fixes #42196.

Change-Id: I1f91498c255c91583950886a89c3c9adc39a32f0
Reviewed-on: https://go-review.googlesource.com/c/go/+/265124
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Paul Murphy <murp@ibm.com>
TryBot-Result: Go Bot <gobot@golang.org>

src/cmd/compile/internal/gc/ssa.go

@@ -3569,13 +3569,17 @@ func init() {
 	alias("runtime/internal/atomic", "LoadAcq", "runtime/internal/atomic", "Load", lwatomics...)
 	alias("runtime/internal/atomic", "LoadAcq64", "runtime/internal/atomic", "Load64", lwatomics...)
 	alias("runtime/internal/atomic", "LoadAcquintptr", "runtime/internal/atomic", "LoadAcq", p4...)
+	alias("sync", "runtime_LoadAcquintptr", "runtime/internal/atomic", "LoadAcq", p4...) // linknamed
 	alias("runtime/internal/atomic", "LoadAcquintptr", "runtime/internal/atomic", "LoadAcq64", p8...)
+	alias("sync", "runtime_LoadAcquintptr", "runtime/internal/atomic", "LoadAcq64", p8...) // linknamed
 	alias("runtime/internal/atomic", "Storeuintptr", "runtime/internal/atomic", "Store", p4...)
 	alias("runtime/internal/atomic", "Storeuintptr", "runtime/internal/atomic", "Store64", p8...)
 	alias("runtime/internal/atomic", "StoreRel", "runtime/internal/atomic", "Store", lwatomics...)
 	alias("runtime/internal/atomic", "StoreRel64", "runtime/internal/atomic", "Store64", lwatomics...)
 	alias("runtime/internal/atomic", "StoreReluintptr", "runtime/internal/atomic", "StoreRel", p4...)
+	alias("sync", "runtime_StoreReluintptr", "runtime/internal/atomic", "StoreRel", p4...) // linknamed
 	alias("runtime/internal/atomic", "StoreReluintptr", "runtime/internal/atomic", "StoreRel64", p8...)
+	alias("sync", "runtime_StoreReluintptr", "runtime/internal/atomic", "StoreRel64", p8...) // linknamed
 	alias("runtime/internal/atomic", "Xchguintptr", "runtime/internal/atomic", "Xchg", p4...)
 	alias("runtime/internal/atomic", "Xchguintptr", "runtime/internal/atomic", "Xchg64", p8...)
 	alias("runtime/internal/atomic", "Xadduintptr", "runtime/internal/atomic", "Xadd", p4...)

src/cmd/go/internal/load/pkg.go

@@ -1338,11 +1338,6 @@ func disallowInternal(srcDir string, importer *Package, importerPath string, p *
 		return p
 	}
 
-	// Allow sync package to access lightweight atomic functions limited to the runtime.
-	if p.Standard && strings.HasPrefix(importerPath, "sync") && p.ImportPath == "runtime/internal/atomic" {
-		return p
-	}
-
 	// Internal is present.
 	// Map import path back to directory corresponding to parent of internal.
 	if i > 0 {

src/sync/pool.go

@@ -7,7 +7,6 @@ package sync
 import (
 	"internal/race"
 	"runtime"
-	runtimeatomic "runtime/internal/atomic"
 	"sync/atomic"
 	"unsafe"
 )
@@ -153,8 +152,8 @@ func (p *Pool) Get() interface{} {
 
 func (p *Pool) getSlow(pid int) interface{} {
 	// See the comment in pin regarding ordering of the loads.
-	size := runtimeatomic.LoadAcquintptr(&p.localSize) // load-acquire
-	locals := p.local                                  // load-consume
+	size := runtime_LoadAcquintptr(&p.localSize) // load-acquire
+	locals := p.local                            // load-consume
 	// Try to steal one element from other procs.
 	for i := 0; i < int(size); i++ {
 		l := indexLocal(locals, (pid+i+1)%int(size))
@@ -166,7 +165,7 @@ func (p *Pool) getSlow(pid int) interface{} {
 	// Try the victim cache. We do this after attempting to steal
 	// from all primary caches because we want objects in the
 	// victim cache to age out if at all possible.
-	size = runtimeatomic.Loaduintptr(&p.victimSize)
+	size = atomic.LoadUintptr(&p.victimSize)
 	if uintptr(pid) >= size {
 		return nil
 	}
@@ -199,8 +198,8 @@ func (p *Pool) pin() (*poolLocal, int) {
 	// Since we've disabled preemption, GC cannot happen in between.
 	// Thus here we must observe local at least as large localSize.
 	// We can observe a newer/larger local, it is fine (we must observe its zero-initialized-ness).
-	s := runtimeatomic.LoadAcquintptr(&p.localSize) // load-acquire
-	l := p.local                                    // load-consume
+	s := runtime_LoadAcquintptr(&p.localSize) // load-acquire
+	l := p.local                              // load-consume
 	if uintptr(pid) < s {
 		return indexLocal(l, pid), pid
 	}
@@ -226,8 +225,8 @@ func (p *Pool) pinSlow() (*poolLocal, int) {
 	// If GOMAXPROCS changes between GCs, we re-allocate the array and lose the old one.
 	size := runtime.GOMAXPROCS(0)
 	local := make([]poolLocal, size)
-	atomic.StorePointer(&p.local, unsafe.Pointer(&local[0]))   // store-release
-	runtimeatomic.StoreReluintptr(&p.localSize, uintptr(size)) // store-release
+	atomic.StorePointer(&p.local, unsafe.Pointer(&local[0])) // store-release
+	runtime_StoreReluintptr(&p.localSize, uintptr(size))     // store-release
 	return &local[pid], pid
 }
 
@@ -283,3 +282,13 @@ func indexLocal(l unsafe.Pointer, i int) *poolLocal {
 func runtime_registerPoolCleanup(cleanup func())
 func runtime_procPin() int
 func runtime_procUnpin()
+
+// The below are implemented in runtime/internal/atomic and the
+// compiler also knows to intrinsify the symbol we linkname into this
+// package.
+
+//go:linkname runtime_LoadAcquintptr runtime/internal/atomic.LoadAcquintptr
+func runtime_LoadAcquintptr(ptr *uintptr) uintptr
+
+//go:linkname runtime_StoreReluintptr runtime/internal/atomic.StoreReluintptr
+func runtime_StoreReluintptr(ptr *uintptr, val uintptr) uintptr