Preliminary support for 'copy' builtin function in exp/eval

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/2157042

src/pkg/exp/eval/expr.go

@@ -1239,6 +1239,38 @@ func (a *exprInfo) compileBuiltinCallExpr(b *block, ft *FuncType, as []*expr) *e
 		}
 		return expr
 
+	case copyType:
+		if !checkCount(2, 2) {
+			return nil
+		}
+		src := as[1]
+		dst := as[0]
+		if src.t != dst.t {
+			a.diag("arguments to built-in function 'copy' must have same type\nsrc: %s\ndst: %s\n", src.t, dst.t)
+			return nil
+		}
+		if _, ok := src.t.lit().(*SliceType); !ok {
+			a.diag("src argument to 'copy' must be a slice (got: %s)", src.t)
+			return nil
+		}
+		if _, ok := dst.t.lit().(*SliceType); !ok {
+			a.diag("dst argument to 'copy' must be a slice (got: %s)", dst.t)
+			return nil
+		}
+		expr := a.newExpr(IntType, "function call")
+		srcf := src.asSlice()
+		dstf := dst.asSlice()
+		expr.eval = func(t *Thread) int64 {
+			src, dst := srcf(t), dstf(t)
+			nelems := src.Len
+			if nelems > dst.Len {
+				nelems = dst.Len
+			}
+			dst.Base.Sub(0, nelems).Assign(t, src.Base.Sub(0, nelems))
+			return nelems
+		}
+		return expr
+
 	case lenType:
 		if !checkCount(1, 1) {
 			return nil

src/pkg/exp/eval/type.go

@@ -712,6 +712,7 @@ var (
 	panicType   = &FuncType{builtin: "panic"}
 	printType   = &FuncType{builtin: "print"}
 	printlnType = &FuncType{builtin: "println"}
+	copyType    = &FuncType{builtin: "copy"}
 )
 
 // Two function types are identical if they have the same number of
@@ -1249,6 +1250,7 @@ func init() {
 	universe.DefineConst("cap", universePos, capType, nil)
 	universe.DefineConst("close", universePos, closeType, nil)
 	universe.DefineConst("closed", universePos, closedType, nil)
+	universe.DefineConst("copy", universePos, copyType, nil)
 	universe.DefineConst("len", universePos, lenType, nil)
 	universe.DefineConst("make", universePos, makeType, nil)
 	universe.DefineConst("new", universePos, newType, nil)