cmd/5g, cmd/8g: fix internal error on 64-bit indices statically bounded

Fixes #4448.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6855100

src/cmd/5g/cgen.c

@@ -521,7 +521,7 @@ ret:
  * returns Prog* to patch to panic call.
  */
 Prog*
-cgenindex(Node *n, Node *res)
+cgenindex(Node *n, Node *res, int bounded)
 {
 	Node tmp, lo, hi, zero, n1, n2;
 
@@ -534,7 +534,7 @@ cgenindex(Node *n, Node *res)
 	cgen(n, &tmp);
 	split64(&tmp, &lo, &hi);
 	gmove(&lo, res);
-	if(debug['B']) {
+	if(bounded) {
 		splitclean();
 		return nil;
 	}
@@ -889,6 +889,7 @@ agenr(Node *n, Node *a, Node *res)
 	Prog *p1, *p2;
 	uint32 w;
 	uint64 v;
+	int bounded;
 
 	if(debug['g'])
 		dump("agenr-n", n);
@@ -915,13 +916,14 @@ agenr(Node *n, Node *a, Node *res)
 	case OINDEX:
 		p2 = nil;  // to be patched to panicindex.
 		w = n->type->width;
+		bounded = debug['B'] || n->bounded;
 		if(nr->addable) {
 			if(!isconst(nr, CTINT))
 				tempname(&tmp, types[TINT32]);
 			if(!isconst(nl, CTSTR))
 				agenr(nl, &n3, res);
 			if(!isconst(nr, CTINT)) {
-				p2 = cgenindex(nr, &tmp);
+				p2 = cgenindex(nr, &tmp, bounded);
 				regalloc(&n1, tmp.type, N);
 				gmove(&tmp, &n1);
 			}
@@ -929,7 +931,7 @@ agenr(Node *n, Node *a, Node *res)
 		if(nl->addable) {
 			if(!isconst(nr, CTINT)) {
 				tempname(&tmp, types[TINT32]);
-				p2 = cgenindex(nr, &tmp);
+				p2 = cgenindex(nr, &tmp, bounded);
 				regalloc(&n1, tmp.type, N);
 				gmove(&tmp, &n1);
 			}
@@ -938,7 +940,7 @@ agenr(Node *n, Node *a, Node *res)
 			}
 		} else {
 			tempname(&tmp, types[TINT32]);
-			p2 = cgenindex(nr, &tmp);
+			p2 = cgenindex(nr, &tmp, bounded);
 			nr = &tmp;
 			if(!isconst(nl, CTSTR))
 				agenr(nl, &n3, res);

src/cmd/5g/gg.h

@@ -88,7 +88,7 @@ void	ginscall(Node*, int);
  * cgen
  */
 void	agen(Node*, Node*);
-Prog* cgenindex(Node *, Node *);
+Prog* cgenindex(Node *, Node *, int);
 void	igen(Node*, Node*, Node*);
 void agenr(Node *n, Node *a, Node *res);
 vlong	fieldoffset(Type*, Node*);

src/cmd/5g/gsubr.c

@@ -1937,7 +1937,7 @@ oindex:
 		t = types[TINT32];
 	regalloc(reg1, t, N);
 	regalloc(&n3, types[TINT32], reg1);
-	p2 = cgenindex(r, &n3);
+	p2 = cgenindex(r, &n3, debug['B'] || n->bounded);
 	gmove(&n3, reg1);
 	regfree(&n3);
 

src/cmd/8g/cgen.c

@@ -464,8 +464,8 @@ flt2:	// binary
  * n is an array index, and might be any size; res width is <= 32-bit.
  * returns Prog* to patch to panic call.
  */
-Prog*
-igenindex(Node *n, Node *res)
+static Prog*
+igenindex(Node *n, Node *res, int bounded)
 {
 	Node tmp, lo, hi, zero;
 
@@ -485,7 +485,7 @@ igenindex(Node *n, Node *res)
 	split64(&tmp, &lo, &hi);
 	tempname(res, types[TUINT32]);
 	gmove(&lo, res);
-	if(debug['B']) {
+	if(bounded) {
 		splitclean();
 		return nil;
 	}
@@ -508,6 +508,7 @@ agen(Node *n, Node *res)
 	uint32 w;
 	uint64 v;
 	Prog *p1, *p2;
+	int bounded;
 
 	if(debug['g']) {
 		dump("\nagen-res", res);
@@ -584,26 +585,27 @@ agen(Node *n, Node *res)
 	case OINDEX:
 		p2 = nil;  // to be patched to panicindex.
 		w = n->type->width;
+		bounded = debug['B'] || n->bounded;
 		if(nr->addable) {
 			// Generate &nl first, and move nr into register.
 			if(!isconst(nl, CTSTR))
 				igen(nl, &n3, res);
 			if(!isconst(nr, CTINT)) {
-				p2 = igenindex(nr, &tmp);
+				p2 = igenindex(nr, &tmp, bounded);
 				regalloc(&n1, tmp.type, N);
 				gmove(&tmp, &n1);
 			}
 		} else if(nl->addable) {
 			// Generate nr first, and move &nl into register.
 			if(!isconst(nr, CTINT)) {
-				p2 = igenindex(nr, &tmp);
+				p2 = igenindex(nr, &tmp, bounded);
 				regalloc(&n1, tmp.type, N);
 				gmove(&tmp, &n1);
 			}
 			if(!isconst(nl, CTSTR))
 				igen(nl, &n3, res);
 		} else {
-			p2 = igenindex(nr, &tmp);
+			p2 = igenindex(nr, &tmp, bounded);
 			nr = &tmp;
 			if(!isconst(nl, CTSTR))
 				igen(nl, &n3, res);

test/fixedbugs/issue4448.go

+// run
+
+// Copyright 2012 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.
+
+// Issue 4448: 64-bit indices that are statically known
+// to be bounded make 5g and 8g generate a dangling branch.
+
+package main
+
+const b26 uint64 = 0x022fdd63cc95386d
+
+var bitPos [64]int
+
+func init() {
+	for p := uint(0); p < 64; p++ {
+		bitPos[b26<<p>>58] = int(p)
+	}
+}
+
+func MinPos(w uint64) int {
+	if w == 0 {
+		panic("bit: MinPos(0) undefined")
+	}
+	return bitPos[((w&-w)*b26)>>58]
+}
+
+func main() {
+	const one = uint64(1)
+	for i := 0; i < 64; i++ {
+		if MinPos(1<<uint(i)) != i {
+			println("i =", i)
+			panic("MinPos(1<<uint(i)) != i")
+		}
+	}
+}