From 53010efe01ce49249eb33d98c29e94394d10e85d Mon Sep 17 00:00:00 2001
From: Ken Thompson <ken@golang.org>
Date: Thu, 28 Aug 2008 19:59:42 -0700
Subject: [PATCH] shift operations to new spec

R=r
OCL=14641
CL=14641
---
 src/cmd/6g/gen.c      | 19 +++++++++++++++++--
 src/cmd/gc/mparith2.c | 15 ++++++++++++---
 src/cmd/gc/walk.c     | 24 +++++++++++++++++++++++-
 3 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/src/cmd/6g/gen.c b/src/cmd/6g/gen.c
index 876f78988f..93035dec2d 100644
--- a/src/cmd/6g/gen.c
+++ b/src/cmd/6g/gen.c
@@ -1077,8 +1077,9 @@ ret:
 void
 cgen_shift(int op, Node *nl, Node *nr, Node *res)
 {
-	Node n1, n2;
+	Node n1, n2, n3;
 	int a, rcl;
+	Prog *p1;
 
 	a = optoas(op, nl->type);
 
@@ -1111,7 +1112,7 @@ cgen_shift(int op, Node *nl, Node *nr, Node *res)
 		goto ret;
 	}
 
-	regalloc(&n2, nl->type, res);	// can one shift the CL register?
+	regalloc(&n2, nl->type, res);	// can one shift the CL register
 	if(nl->ullman >= nr->ullman) {
 		cgen(nl, &n2);
 		cgen(nr, &n1);
@@ -1119,7 +1120,21 @@ cgen_shift(int op, Node *nl, Node *nr, Node *res)
 		cgen(nr, &n1);
 		cgen(nl, &n2);
 	}
+
+	// test and fix up large shifts
+	nodconst(&n3, types[TUINT32], nl->type->width*8);
+	gins(optoas(OCMP, types[TUINT32]), &n1, &n3);
+	p1 = gbranch(optoas(OLT, types[TUINT32]), T);
+	if(op == ORSH && issigned[nl->type->etype]) {
+		nodconst(&n3, types[TUINT32], nl->type->width*8-1);
+		gins(a, &n3, &n2);
+	} else {
+		nodconst(&n3, nl->type, 0);
+		gmove(&n3, &n2);
+	}
+	patch(p1, pc);
 	gins(a, &n1, &n2);
+
 	gmove(&n2, res);
 
 	regfree(&n1);
diff --git a/src/cmd/gc/mparith2.c b/src/cmd/gc/mparith2.c
index ecc4c1d870..b819bd4006 100644
--- a/src/cmd/gc/mparith2.c
+++ b/src/cmd/gc/mparith2.c
@@ -71,10 +71,11 @@ mplshw(Mpint *a)
 static void
 mprsh(Mpint *a)
 {
-	long *a1, x;
+	long *a1, x, lo;
 	int i, c;
 
 	c = 0;
+	lo = a->a[0] & 1;
 	a1 = &a->a[Mpprec];
 	for(i=0; i<Mpprec; i++) {
 		x = *--a1;
@@ -83,6 +84,8 @@ mprsh(Mpint *a)
 		if(x & 1)
 			c = Mpbase;
 	}
+	if(a->neg && lo == 0)
+		mpaddcfix(a, -1);
 }
 
 //
@@ -92,15 +95,18 @@ mprsh(Mpint *a)
 static void
 mprshw(Mpint *a)
 {
-	long *a1;
+	long *a1, lo;
 	int i;
 
+	lo = a->a[0];
 	a1 = &a->a[0];
 	for(i=1; i<Mpprec; i++) {
 		a1[0] = a1[1];
 		*a1++;
 	}
 	a1[0] = 0;
+	if(a->neg && lo == 0)
+		mpaddcfix(a, -1);
 }
 
 //
@@ -411,7 +417,10 @@ mprshfixfix(Mpint *a, Mpint *b)
 	s = mpgetfix(b);
 	if(s < 0 || s >= Mpprec*Mpscale) {
 		warn("stupid shift: %lld", s);
-		mpmovecfix(a, 0);
+		if(a->neg)
+			mpmovecfix(a, -1);
+		else
+			mpmovecfix(a, 0);
 		return;
 	}
 
diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index 23ec5dbc3b..b018e999c2 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -473,8 +473,11 @@ loop:
 			goto nottop;
 		walktype(n->left, Elv);
 		l = n->left;
-		if(l->op != OINDEX)
+		if(l->op != OINDEX) {
+			if(n->etype == OLSH || n->etype == ORSH)
+				goto shft;
 			goto com;
+		}
 		if(!isptrto(l->left->type, TMAP))
 			goto com;
 		*n = *mapop(n, top);
@@ -482,6 +485,25 @@ loop:
 
 	case OLSH:
 	case ORSH:
+		if(top != Erv)
+			goto nottop;
+		walktype(n->left, Erv);
+
+	shft:
+		walktype(n->right, Erv);
+		if(n->left == N || n->right == N)
+			goto ret;
+		evconst(n);
+		if(n->op == OLITERAL)
+			goto ret;
+		convlit(n->left, n->left->type);
+		convlit(n->right, types[TUINT32]);
+		if(n->left->type == T || n->right->type == T)
+			goto ret;
+		if(issigned[n->right->type->etype])
+			goto badt;
+		break;
+
 	case OMOD:
 	case OAND:
 	case OOR:
-- 
2.48.1