cmd/compile: small Mpint method simplifications

Get rid of (*Mpint).Add's "quiet" parameter: it's always set to 0.

Inline (*Mpint).shift into (*Mpint).Lsh and (*Mpint).Rsh. There's no
need for a common shift method that can handle both left or right
shifts based on sign when the higher level abstractions only ever do
one or the other.

Change-Id: Icd3b082413f9193961b6835279e0bd4b6a6a6621
Reviewed-on: https://go-review.googlesource.com/21050
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -833,7 +833,7 @@ func evconst(n *Node) {
 
 	case OADD_ | CTINT_,
 		OADD_ | CTRUNE_:
-		v.U.(*Mpint).Add(rv.U.(*Mpint), 0)
+		v.U.(*Mpint).Add(rv.U.(*Mpint))
 
 	case OSUB_ | CTINT_,
 		OSUB_ | CTRUNE_:

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

@@ -68,7 +68,7 @@ func (a *Mpint) SetFloat(b *Mpflt) int {
 	return -1
 }
 
-func (a *Mpint) Add(b *Mpint, quiet int) {
+func (a *Mpint) Add(b *Mpint) {
 	if a.Ovf || b.Ovf {
 		if nsavederrors+nerrors == 0 {
 			Yyerror("ovf in mpaddfixfix")
@@ -79,7 +79,7 @@ func (a *Mpint) Add(b *Mpint, quiet int) {
 
 	a.Val.Add(&a.Val, &b.Val)
 
-	if a.checkOverflow(0) && quiet == 0 {
+	if a.checkOverflow(0) {
 		Yyerror("constant addition overflow")
 	}
 }
@@ -198,20 +198,6 @@ func (a *Mpint) Xor(b *Mpint) {
 	a.Val.Xor(&a.Val, &b.Val)
 }
 
-// shift left by s (or right by -s)
-func (a *Mpint) shift(s int) {
-	switch {
-	case s > 0:
-		if a.checkOverflow(s) {
-			Yyerror("constant shift overflow")
-			return
-		}
-		a.Val.Lsh(&a.Val, uint(s))
-	case s < 0:
-		a.Val.Rsh(&a.Val, uint(-s))
-	}
-}
-
 func (a *Mpint) Lsh(b *Mpint) {
 	if a.Ovf || b.Ovf {
 		if nsavederrors+nerrors == 0 {
@@ -232,7 +218,11 @@ func (a *Mpint) Lsh(b *Mpint) {
 		return
 	}
 
-	a.shift(int(s))
+	if a.checkOverflow(int(s)) {
+		Yyerror("constant shift overflow")
+		return
+	}
+	a.Val.Lsh(&a.Val, uint(s))
 }
 
 func (a *Mpint) Rsh(b *Mpint) {
@@ -255,7 +245,7 @@ func (a *Mpint) Rsh(b *Mpint) {
 		return
 	}
 
-	a.shift(int(-s))
+	a.Val.Rsh(&a.Val, uint(s))
 }
 
 func (a *Mpint) Cmp(b *Mpint) int {

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

@@ -3318,7 +3318,7 @@ func (p *parser) hidden_constant() *Node {
 
 		if s2.Val().Ctype() == CTRUNE && s4.Val().Ctype() == CTINT {
 			ss := s2
-			s2.Val().U.(*Mpint).Add(s4.Val().U.(*Mpint), 0)
+			s2.Val().U.(*Mpint).Add(s4.Val().U.(*Mpint))
 			return ss
 		}
 		s4.Val().U.(*Mpcplx).Real = s4.Val().U.(*Mpcplx).Imag