cmd/compile: reduce reliance on implementation details of Mpint

Change-Id: Ifdc41f6c77c83d22b9ad8811280f1e1db051c781
Reviewed-on: https://go-review.googlesource.com/39951
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -309,8 +309,9 @@ func convlit1(n *Node, t *types.Type, explicit bool, reuse canReuseNode) *Node {
 		// if it is an unsafe.Pointer
 		case TUINTPTR:
 			if n.Type.Etype == TUNSAFEPTR {
-				n.SetVal(Val{new(Mpint)})
-				n.Val().U.(*Mpint).SetInt64(0)
+				i := new(Mpint)
+				i.SetInt64(0)
+				n.SetVal(Val{i})
 			} else {
 				goto bad
 			}
@@ -458,7 +459,7 @@ func toint(v Val) Val {
 	case *Mpflt:
 		i := new(Mpint)
 		if !i.SetFloat(u) {
-			if i.Ovf {
+			if i.checkOverflow(0) {
 				yyerror("integer too large")
 			} else {
 				// The value of u cannot be represented as an integer;
@@ -1518,7 +1519,7 @@ func nonnegintconst(n *Node) int64 {
 	// Mpint, so we still have to guard the conversion.
 	v := toint(n.Val())
 	vi, ok := v.U.(*Mpint)
-	if !ok || vi.Val.Sign() < 0 || vi.Cmp(maxintval[TINT32]) > 0 {
+	if !ok || vi.CmpInt64(0) < 0 || vi.Cmp(maxintval[TINT32]) > 0 {
 		return -1
 	}
 

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

@@ -38,7 +38,7 @@ func newMpflt() *Mpflt {
 }
 
 func (a *Mpflt) SetInt(b *Mpint) {
-	if b.Ovf {
+	if b.checkOverflow(0) {
 		// sign doesn't really matter but copy anyway
 		a.Val.SetInf(b.Val.Sign() < 0)
 		return

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

@@ -5,16 +5,20 @@
 package gc
 
 import (
-	"math/big"
 	"testing"
 )
 
 func nodrune(r rune) *Node {
-	return nodlit(Val{&Mpint{Val: *big.NewInt(int64(r)), Rune: true}})
+	v := new(Mpint)
+	v.SetInt64(int64(r))
+	v.Rune = true
+	return nodlit(Val{v})
 }
 
 func nodflt(f float64) *Node {
-	return nodlit(Val{&Mpflt{Val: *big.NewFloat(f)}})
+	v := new(Mpflt)
+	v.SetFloat64(f)
+	return nodlit(Val{v})
 }
 
 func TestCaseClauseByConstVal(t *testing.T) {