cmd/gc: accept ideal float as indices.

Fixes #4813.

R=golang-dev, daniel.morsing, rsc
CC=golang-dev
https://golang.org/cl/7625050

src/cmd/gc/typecheck.c

@@ -276,6 +276,29 @@ callrecvlist(NodeList *l)
 	return 0;
 }
 
+// indexlit implements typechecking of untyped values as
+// array/slice indexes. It is equivalent to defaultlit
+// except for constants of numerical kind, which are acceptable
+// whenever they can be represented by a value of type int.
+static void
+indexlit(Node **np)
+{
+	Node *n;
+
+	n = *np;
+	if(n == N || !isideal(n->type))
+		return;
+	switch(consttype(n)) {
+	case CTINT:
+	case CTRUNE:
+	case CTFLT:
+	case CTCPLX:
+		defaultlit(np, types[TINT]);
+		break;
+	}
+	defaultlit(np, T);
+}
+
 static void
 typecheck1(Node **np, int top)
 {
@@ -845,7 +868,7 @@ reswitch:
 
 		case TSTRING:
 		case TARRAY:
-			defaultlit(&n->right, T);
+			indexlit(&n->right);
 			if(t->etype == TSTRING)
 				n->type = types[TUINT8];
 			else
@@ -861,8 +884,8 @@ reswitch:
 				yyerror("non-integer %s index %N", why, n->right);
 				break;
 			}
-			if(n->right->op == OLITERAL) {
-			       	if(mpgetfix(n->right->val.u.xval) < 0)
+			if(isconst(n->right, CTINT)) {
+				if(mpgetfix(n->right->val.u.xval) < 0)
 					yyerror("invalid %s index %N (index must be non-negative)", why, n->right);
 				else if(isfixedarray(t) && t->bound > 0 && mpgetfix(n->right->val.u.xval) >= t->bound)
 					yyerror("invalid array index %N (out of bounds for %d-element array)", n->right, t->bound);
@@ -938,8 +961,8 @@ reswitch:
 		typecheck(&n->right->left, Erv);
 		typecheck(&n->right->right, Erv);
 		defaultlit(&n->left, T);
-		defaultlit(&n->right->left, T);
-		defaultlit(&n->right->right, T);
+		indexlit(&n->right->left);
+		indexlit(&n->right->right);
 		l = n->left;
 		if(isfixedarray(l->type)) {
 			if(!islvalue(n->left)) {

test/fixedbugs/issue4813.go

@@ -0,0 +1,52 @@
+// errorcheck
+
+// Copyright 2013 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 4813: use of constant floats as indices.
+
+package main
+
+var A [3]int
+var S []int
+var T string
+
+const (
+	i  = 1
+	f  = 2.0
+	f2 = 2.1
+	c  = complex(2, 0)
+	c2 = complex(2, 1)
+)
+
+var (
+	vf = f
+	vc = c
+)
+
+var (
+	a1 = A[i]
+	a2 = A[f]
+	a3 = A[f2] // ERROR "truncated"
+	a4 = A[c]
+	a5 = A[c2] // ERROR "truncated"
+	a6 = A[vf] // ERROR "non-integer"
+	a7 = A[vc] // ERROR "non-integer"
+
+	s1 = S[i]
+	s2 = S[f]
+	s3 = S[f2] // ERROR "truncated"
+	s4 = S[c]
+	s5 = S[c2] // ERROR "truncated"
+	s6 = S[vf] // ERROR "non-integer"
+	s7 = S[vc] // ERROR "non-integer"
+
+	t1 = T[i]
+	t2 = T[f]
+	t3 = T[f2] // ERROR "truncated"
+	t4 = T[c]
+	t5 = T[c2] // ERROR "truncated"
+	t6 = T[vf] // ERROR "non-integer"
+	t7 = T[vc] // ERROR "non-integer"
+)

test/index.go

@@ -36,6 +36,8 @@ const (
 	ci64big int64 = 1<<31
 	ci64bigger int64 = 1<<32
 	chuge = 1<<100
+	cfgood = 2.0
+	cfbad = 2.1
 
 	cnj = -2
 	cni int = -3
@@ -46,6 +48,8 @@ const (
 	cni64big int64 = -1<<31
 	cni64bigger int64 = -1<<32
 	cnhuge = -1<<100
+	cnfgood = -2.0
+	cnfbad = -2.1
 )
 
 var j int = 100020
@@ -57,6 +61,8 @@ var i64 int64 = 100023
 var i64big int64 = 1<<31
 var i64bigger int64 = 1<<32
 var huge uint64 = 1<<64 - 1
+var fgood float64 = 2.0
+var fbad float64 = 2.1
 
 var nj int = -10
 var ni int = -11
@@ -67,6 +73,8 @@ var ni64 int64 = -13
 var ni64big int64 = -1<<31
 var ni64bigger int64 = -1<<32
 var nhuge int64 = -1<<63
+var nfgood float64 = -2.0
+var nfbad float64 = -2.1
 
 var si []int = make([]int, 10)
 var ai [10]int
@@ -156,7 +164,7 @@ func testExpr(b *bufio.Writer, expr string) {
 	if pass == 0 {
 		fmt.Fprintf(b, "\ttest(func(){use(%s)}, %q)\n", expr, expr)
 	} else {
-		fmt.Fprintf(b, "\tuse(%s)  // ERROR \"index|overflow\"\n", expr)
+		fmt.Fprintf(b, "\tuse(%s)  // ERROR \"index|overflow|truncated\"\n", expr)
 	}
 }
 
@@ -169,15 +177,15 @@ func main() {
 		fmt.Fprint(b, "// errorcheck\n\n")
 	}
 	fmt.Fprint(b, prolog)
-	
+
 	var choices = [][]string{
 		// Direct value, fetch from struct, fetch from struct pointer.
 		// The last two cases get us to oindex_const_sudo in gsubr.c.
 		[]string{"", "t.", "pt."},
-		
+
 		// Array, pointer to array, slice.
 		[]string{"a", "pa", "s"},
-		
+
 		// Element is int, element is quad (struct).
 		// This controls whether we end up in gsubr.c (i) or cgen.c (q).
 		[]string{"i", "q"},
@@ -192,9 +200,9 @@ func main() {
 		[]string{"", "n"},
 
 		// Size of index.
-		[]string{"j", "i", "i8", "i16", "i32", "i64", "i64big", "i64bigger", "huge"},
+		[]string{"j", "i", "i8", "i16", "i32", "i64", "i64big", "i64bigger", "huge", "fgood", "fbad"},
 	}
-	
+
 	forall(choices, func(x []string) {
 		p, a, e, big, c, n, i := x[0], x[1], x[2], x[3], x[4], x[5], x[6]
 
@@ -206,7 +214,7 @@ func main() {
 		//	negative constant
 		//	large constant
 		thisPass := 0
-		if c == "c" && (a == "a" || a == "pa" || n == "n" || i == "i64big" || i == "i64bigger" || i == "huge") {
+		if c == "c" && (a == "a" || a == "pa" || n == "n" || i == "i64big" || i == "i64bigger" || i == "huge" || i == "fbad") {
 			if i == "huge" {
 				// Due to a detail of 6g's internals,
 				// the huge constant errors happen in an
@@ -223,27 +231,50 @@ func main() {
 				thisPass = 2
 			}
 		}
-		
+
+		pae := p + a + e + big
+		cni := c + n + i
+
 		// If we're using the big-len data, positive int8 and int16 cannot overflow.
 		if big == "b" && n == "" && (i == "i8" || i == "i16") {
+			if pass == 0 {
+				fmt.Fprintf(b, "\tuse(%s[%s])\n", pae, cni)
+				fmt.Fprintf(b, "\tuse(%s[0:%s])\n", pae, cni)
+				fmt.Fprintf(b, "\tuse(%s[1:%s])\n", pae, cni)
+				fmt.Fprintf(b, "\tuse(%s[%s:])\n", pae, cni)
+				fmt.Fprintf(b, "\tuse(%s[%s:%s])\n", pae, cni, cni)
+			}
+			return
+		}
+
+		// Float variables cannot be used as indices.
+		if c == "" && (i == "fgood" || i == "fbad") {
+			return
+		}
+		// Integral float constat is ok.
+		if c == "c" && n == "" && i == "fgood" {
+			if pass == 0 {
+				fmt.Fprintf(b, "\tuse(%s[%s])\n", pae, cni)
+				fmt.Fprintf(b, "\tuse(%s[0:%s])\n", pae, cni)
+				fmt.Fprintf(b, "\tuse(%s[1:%s])\n", pae, cni)
+				fmt.Fprintf(b, "\tuse(%s[%s:])\n", pae, cni)
+				fmt.Fprintf(b, "\tuse(%s[%s:%s])\n", pae, cni, cni)
+			}
 			return
 		}
 
 		// Only print the test case if it is appropriate for this pass.
 		if thisPass == pass {
-			pae := p+a+e+big
-			cni := c+n+i
-			
 			// Index operation
-			testExpr(b, pae + "[" + cni + "]")
-			
+			testExpr(b, pae+"["+cni+"]")
+
 			// Slice operation.
 			// Low index 0 is a special case in ggen.c
 			// so test both 0 and 1.
-			testExpr(b, pae + "[0:" + cni + "]")
-			testExpr(b, pae + "[1:" + cni + "]")
-			testExpr(b, pae + "[" + cni + ":]")
-			testExpr(b, pae + "[" + cni + ":" + cni + "]")
+			testExpr(b, pae+"[0:"+cni+"]")
+			testExpr(b, pae+"[1:"+cni+"]")
+			testExpr(b, pae+"["+cni+":]")
+			testExpr(b, pae+"["+cni+":"+cni+"]")
 		}
 	})
 
@@ -253,7 +284,7 @@ func main() {
 
 func forall(choices [][]string, f func([]string)) {
 	x := make([]string, len(choices))
-	
+
 	var recurse func(d int)
 	recurse = func(d int) {
 		if d >= len(choices) {
@@ -261,7 +292,7 @@ func forall(choices [][]string, f func([]string)) {
 			return
 		}
 		for _, x[d] = range choices[d] {
-			recurse(d+1)
+			recurse(d + 1)
 		}
 	}
 	recurse(0)