cmd/compile: redo IsRuntimePkg/IsReflectPkg predicate

Currently, the types package has IsRuntimePkg and IsReflectPkg
predicates for testing if a Pkg is the runtime or reflect packages.
IsRuntimePkg returns "true" for any "CompilingRuntime" package, which
includes all of the packages imported by the runtime. This isn't
inherently wrong, except that all but one use of it is of the form "is
this Sym a specific runtime.X symbol?" for which we clearly only want
the package "runtime" itself. IsRuntimePkg was introduced (as
isRuntime) in CL 37538 as part of separating the real runtime package
from the compiler built-in fake runtime package. As of that CL, the
"runtime" package couldn't import any other packages, so this was
adequate at the time.

We could fix this by just changing the implementation of IsRuntimePkg,
but the meaning of this API is clearly somewhat ambiguous. Instead, we
replace it with a new RuntimeSymName function that returns the name of
a symbol if it's in package "runtime", or "" if not. This is what
every call site (except one) actually wants, which lets us simplify
the callers, and also more clearly addresses the ambiguity between
package "runtime" and the general concept of a runtime package.

IsReflectPkg doesn't have the same issue of ambiguity, but it
parallels IsRuntimePkg and is used in the same way, so we replace it
with a new ReflectSymName for consistency.

Change-Id: If3a81d7d11732a9ab2cac9488d17508415cfb597
Reviewed-on: https://go-review.googlesource.com/c/go/+/521696
Reviewed-by: Cuong Manh Le <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>
Run-TryBot: Austin Clements <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

src/cmd/compile/internal/inline/inl.go

@@ -505,6 +505,7 @@ func (v *hairyVisitor) doNode(n ir.Node) bool {
 	if n == nil {
 		return false
 	}
+opSwitch:
 	switch n.Op() {
 	// Call is okay if inlinable and we have the budget for the body.
 	case ir.OCALLFUNC:
@@ -516,22 +517,19 @@ func (v *hairyVisitor) doNode(n ir.Node) bool {
 		var cheap bool
 		if n.X.Op() == ir.ONAME {
 			name := n.X.(*ir.Name)
-			if name.Class == ir.PFUNC && types.IsRuntimePkg(name.Sym().Pkg) {
-				fn := name.Sym().Name
-				if fn == "getcallerpc" || fn == "getcallersp" {
+			if name.Class == ir.PFUNC {
+				switch fn := types.RuntimeSymName(name.Sym()); fn {
+				case "getcallerpc", "getcallersp":
 					v.reason = "call to " + fn
 					return true
-				}
-				if fn == "throw" {
+				case "throw":
 					v.budget -= inlineExtraThrowCost
-					break
+					break opSwitch
 				}
-			}
-			// Special case for reflect.noescpae. It does just type
-			// conversions to appease the escape analysis, and doesn't
-			// generate code.
-			if name.Class == ir.PFUNC && types.IsReflectPkg(name.Sym().Pkg) {
-				if name.Sym().Name == "noescape" {
+				// Special case for reflect.noescape. It does just type
+				// conversions to appease the escape analysis, and doesn't
+				// generate code.
+				if types.ReflectSymName(name.Sym()) == "noescape" {
 					cheap = true
 				}
 			}
@@ -553,7 +551,7 @@ func (v *hairyVisitor) doNode(n ir.Node) bool {
 			if meth := ir.MethodExprName(n.X); meth != nil {
 				if fn := meth.Func; fn != nil {
 					s := fn.Sym()
-					if types.IsRuntimePkg(s.Pkg) && s.Name == "heapBits.nextArena" {
+					if types.RuntimeSymName(s) == "heapBits.nextArena" {
 						// Special case: explicitly allow mid-stack inlining of
 						// runtime.heapBits.next even though it calls slow-path
 						// runtime.heapBits.nextArena.
@@ -906,8 +904,11 @@ func inlnode(callerfn *ir.Func, n ir.Node, bigCaller bool, inlCalls *[]*ir.Inlin
 			// even when package reflect was compiled without it (#35073).
 			if meth := ir.MethodExprName(n.X); meth != nil {
 				s := meth.Sym()
-				if base.Debug.Checkptr != 0 && types.IsReflectPkg(s.Pkg) && (s.Name == "Value.UnsafeAddr" || s.Name == "Value.Pointer") {
-					return n
+				if base.Debug.Checkptr != 0 {
+					switch types.ReflectSymName(s) {
+					case "Value.UnsafeAddr", "Value.Pointer":
+						return n
+					}
 				}
 			}
 		}

src/cmd/compile/internal/noder/unified.go

@@ -109,7 +109,7 @@ func unified(m posMap, noders []*noder) {
 	// For functions originally came from package runtime,
 	// mark as norace to prevent instrumenting, see issue #60439.
 	for _, fn := range target.Funcs {
-		if !base.Flag.CompilingRuntime && types.IsRuntimePkg(fn.Sym().Pkg) {
+		if !base.Flag.CompilingRuntime && types.RuntimeSymName(fn.Sym()) != "" {
 			fn.Pragma |= ir.Norace
 		}
 	}

src/cmd/compile/internal/ssagen/nowb.go

@@ -82,7 +82,7 @@ func (c *nowritebarrierrecChecker) findExtraCalls(nn ir.Node) {
 	if fn.Class != ir.PFUNC || fn.Defn == nil {
 		return
 	}
-	if !types.IsRuntimePkg(fn.Sym().Pkg) || fn.Sym().Name != "systemstack" {
+	if types.RuntimeSymName(fn.Sym()) != "systemstack" {
 		return
 	}
 

src/cmd/compile/internal/typecheck/func.go

@@ -278,7 +278,7 @@ func tcCall(n *ir.CallExpr, top int) ir.Node {
 		n.SetType(l.Type().Result(0).Type)
 
 		if n.Op() == ir.OCALLFUNC && n.X.Op() == ir.ONAME {
-			if sym := n.X.(*ir.Name).Sym(); types.IsRuntimePkg(sym.Pkg) && sym.Name == "getg" {
+			if sym := n.X.(*ir.Name).Sym(); types.RuntimeSymName(sym) == "getg" {
 				// Emit code for runtime.getg() directly instead of calling function.
 				// Most such rewrites (for example the similar one for math.Sqrt) should be done in walk,
 				// so that the ordering pass can make sure to preserve the semantics of the original code

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

@@ -1841,17 +1841,22 @@ func IsMethodApplicable(t *Type, m *Field) bool {
 	return t.IsPtr() || !m.Type.Recv().Type.IsPtr() || IsInterfaceMethod(m.Type) || m.Embedded == 2
 }
 
-// IsRuntimePkg reports whether p is package runtime.
-func IsRuntimePkg(p *Pkg) bool {
-	if base.Flag.CompilingRuntime && p == LocalPkg {
-		return true
+// RuntimeSymName returns the name of s if it's in package "runtime"; otherwise
+// it returns "".
+func RuntimeSymName(s *Sym) string {
+	if s.Pkg.Path == "runtime" {
+		return s.Name
 	}
-	return p.Path == "runtime"
+	return ""
 }
 
-// IsReflectPkg reports whether p is package reflect.
-func IsReflectPkg(p *Pkg) bool {
-	return p.Path == "reflect"
+// ReflectSymName returns the name of s if it's in package "reflect"; otherwise
+// it returns "".
+func ReflectSymName(s *Sym) string {
+	if s.Pkg.Path == "reflect" {
+		return s.Name
+	}
+	return ""
 }
 
 // IsNoInstrumentPkg reports whether p is a package that

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

@@ -631,7 +631,7 @@ func walkPrint(nn *ir.CallExpr, init *ir.Nodes) ir.Node {
 			on = typecheck.LookupRuntime("printslice")
 			on = typecheck.SubstArgTypes(on, n.Type()) // any-1
 		case types.TUINT, types.TUINT8, types.TUINT16, types.TUINT32, types.TUINT64, types.TUINTPTR:
-			if types.IsRuntimePkg(n.Type().Sym().Pkg) && n.Type().Sym().Name == "hex" {
+			if types.RuntimeSymName(n.Type().Sym()) == "hex" {
 				on = typecheck.LookupRuntime("printhex")
 			} else {
 				on = typecheck.LookupRuntime("printuint")

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

@@ -993,7 +993,7 @@ func usemethod(n *ir.CallExpr) {
 
 	// Check that first result type is "reflect.Method". Note that we have to check sym name and sym package
 	// separately, as we can't check for exact string "reflect.Method" reliably (e.g., see #19028 and #38515).
-	if s := t.Result(0).Type.Sym(); s != nil && s.Name == "Method" && types.IsReflectPkg(s.Pkg) {
+	if s := t.Result(0).Type.Sym(); s != nil && types.ReflectSymName(s) == "Method" {
 		ir.CurFunc.SetReflectMethod(true)
 		// The LSym is initialized at this point. We need to set the attribute on the LSym.
 		ir.CurFunc.LSym.Set(obj.AttrReflectMethod, true)

test/nowritebarrier.go

@@ -1,12 +1,14 @@
-// errorcheck -+
+// errorcheck -+ -p=runtime
 
 // Copyright 2016 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.
 
 // Test go:nowritebarrier and related directives.
+// This must appear to be in package runtime so the compiler
+// recognizes "systemstack".
 
-package p
+package runtime
 
 type t struct {
 	f *t