1 files changed, 108 insertions, 0 deletions
diff --git a/libgo/go/cmd/vet/dead.go b/libgo/go/cmd/vet/dead.go
new file mode 100644
index 0000000..130f619
--- /dev/null
+++ b/libgo/go/cmd/vet/dead.go
@@ -0,0 +1,108 @@
+// Copyright 2017 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.
+//
+// Simplified dead code detector. Used for skipping certain checks
+// on unreachable code (for instance, shift checks on arch-specific code).
+
+package main
+
+import (
+	"go/ast"
+	"go/constant"
+)
+
+// updateDead puts unreachable "if" and "case" nodes into f.dead.
+func (f *File) updateDead(node ast.Node) {
+	if f.dead[node] {
+		// The node is already marked as dead.
+		return
+	}
+
+	switch stmt := node.(type) {
+	case *ast.IfStmt:
+		// "if" branch is dead if its condition evaluates
+		// to constant false.
+		v := f.pkg.types[stmt.Cond].Value
+		if v == nil {
+			return
+		}
+		if !constant.BoolVal(v) {
+			f.setDead(stmt.Body)
+			return
+		}
+		f.setDead(stmt.Else)
+	case *ast.SwitchStmt:
+		// Case clause with empty switch tag is dead if it evaluates
+		// to constant false.
+		if stmt.Tag == nil {
+		BodyLoopBool:
+			for _, stmt := range stmt.Body.List {
+				cc := stmt.(*ast.CaseClause)
+				if cc.List == nil {
+					// Skip default case.
+					continue
+				}
+				for _, expr := range cc.List {
+					v := f.pkg.types[expr].Value
+					if v == nil || constant.BoolVal(v) {
+						continue BodyLoopBool
+					}
+				}
+				f.setDead(cc)
+			}
+			return
+		}
+
+		// Case clause is dead if its constant value doesn't match
+		// the constant value from the switch tag.
+		// TODO: This handles integer comparisons only.
+		v := f.pkg.types[stmt.Tag].Value
+		if v == nil || v.Kind() != constant.Int {
+			return
+		}
+		tagN, ok := constant.Uint64Val(v)
+		if !ok {
+			return
+		}
+	BodyLoopInt:
+		for _, x := range stmt.Body.List {
+			cc := x.(*ast.CaseClause)
+			if cc.List == nil {
+				// Skip default case.
+				continue
+			}
+			for _, expr := range cc.List {
+				v := f.pkg.types[expr].Value
+				if v == nil {
+					continue BodyLoopInt
+				}
+				n, ok := constant.Uint64Val(v)
+				if !ok || tagN == n {
+					continue BodyLoopInt
+				}
+			}
+			f.setDead(cc)
+		}
+	}
+}
+
+// setDead marks the node and all the children as dead.
+func (f *File) setDead(node ast.Node) {
+	dv := deadVisitor{
+		f: f,
+	}
+	ast.Walk(dv, node)
+}
+
+type deadVisitor struct {
+	f *File
+}
+
+func (dv deadVisitor) Visit(node ast.Node) ast.Visitor {
+	if node == nil {
+		return nil
+	}
+	dv.f.dead[node] = true
+	return dv
+}