gc: avoid meaningless constant overflow error for inverted slice range

Used to say:

issue4251.go:12: inverted slice range
issue4251.go:12: constant -1 overflows uint64
issue4251.go:16: inverted slice range
issue4251.go:16: constant -1 overflows uint64
issue4251.go:20: inverted slice range
issue4251.go:20: constant -1 overflows uint64

With this patch, only gives the "inverted slice range" errors.

R=golang-dev, daniel.morsing
CC=golang-dev
https://golang.org/cl/6871058

diff --git a/src/cmd/gc/typecheck.c b/src/cmd/gc/typecheck.c
index 2b6af2b6de0f94fa583888960fc7fc351ba01e4a..78e2047a6e41fc62d678ffbe3497742f3a2950bd 100644 (file)
--- a/src/cmd/gc/typecheck.c
+++ b/src/cmd/gc/typecheck.c
@@ -950,12 +950,16 @@ reswitch:
                                goto error;
                        }
                        if(n->right->left->op == OLITERAL) {
-                               if(mpgetfix(n->right->left->val.u.xval) < 0)
+                               if(mpgetfix(n->right->left->val.u.xval) < 0) {
                                        yyerror("invalid slice index %N (index must be non-negative)", n->right->left);
-                               else if(tp != nil && tp->bound > 0 && mpgetfix(n->right->left->val.u.xval) > tp->bound)
+                                       goto error;
+                               } else if(tp != nil && tp->bound > 0 && mpgetfix(n->right->left->val.u.xval) > tp->bound) {
                                        yyerror("invalid slice index %N (out of bounds for %d-element array)", n->right->left, tp->bound);
-                               else if(mpcmpfixfix(n->right->left->val.u.xval, maxintval[TINT]) > 0)
+                                       goto error;
+                               } else if(mpcmpfixfix(n->right->left->val.u.xval, maxintval[TINT]) > 0) {
                                        yyerror("invalid slice index %N (index too large)", n->right->left);
+                                       goto error;
+                               }
                        }
                }
                if(n->right->right != N) {
@@ -966,14 +970,26 @@ reswitch:
                                goto error;
                        }
                        if(n->right->right->op == OLITERAL) {
-                               if(mpgetfix(n->right->right->val.u.xval) < 0)
+                               if(mpgetfix(n->right->right->val.u.xval) < 0) {
                                        yyerror("invalid slice index %N (index must be non-negative)", n->right->right);
-                               else if(tp != nil && tp->bound > 0 && mpgetfix(n->right->right->val.u.xval) > tp->bound)
+                                       goto error;
+                               } else if(tp != nil && tp->bound > 0 && mpgetfix(n->right->right->val.u.xval) > tp->bound) {
                                        yyerror("invalid slice index %N (out of bounds for %d-element array)", n->right->right, tp->bound);
-                               else if(mpcmpfixfix(n->right->right->val.u.xval, maxintval[TINT]) > 0)
+                                       goto error;
+                               } else if(mpcmpfixfix(n->right->right->val.u.xval, maxintval[TINT]) > 0) {
                                        yyerror("invalid slice index %N (index too large)", n->right->right);
+                                       goto error;
+                               }
                        }
                }
+               if(n->right->left != N
+                  && n->right->right != N
+                  && n->right->left->op == OLITERAL
+                  && n->right->right->op == OLITERAL
+                  && mpcmpfixfix(n->right->left->val.u.xval, n->right->right->val.u.xval) > 0) {
+                       yyerror("inverted slice index %N > %N", n->right->left, n->right->right);
+                       goto error;
+               }
                goto ret;
 
        /*

diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index ee8a481f0648c6c00e50c4193b1c262820e5c604..98b2a4fa74421758a9bbe9533f5b2edaa03eae5b 100644 (file)
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -2517,8 +2517,6 @@ sliceany(Node* n, NodeList **init)
                else
                        bv = mpgetfix(bound->val.u.xval);
        }
-       lbv = -1;
-       hbv = -1;
 
        if(isconst(hb, CTINT)) {
                hbv = mpgetfix(hb->val.u.xval);
@@ -2536,8 +2534,6 @@ sliceany(Node* n, NodeList **init)
                if(lbv == 0)
                        lb = N;
        }
-       if(lbv >= 0 && hbv >= 0 && lbv > hbv)
-               yyerror("inverted slice range");
 
        // dynamic checks convert all bounds to unsigned to save us the bound < 0 comparison
        // generate

diff --git a/test/fixedbugs/issue4251.go b/test/fixedbugs/issue4251.go
new file mode 100644 (file)
index 0000000..a14e089
--- /dev/null
+++ b/test/fixedbugs/issue4251.go
@@ -0,0 +1,21 @@
+// errorcheck
+
+// 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 4251: slice with inverted range is an error.
+
+package p
+
+func F1(s []byte) []byte {
+       return s[2:1]           // ERROR "inverted"
+}
+
+func F2(a [10]byte) []byte {
+       return a[2:1]           // ERROR "inverted"
+}
+
+func F3(s string) string {
+       return s[2:1]           // ERROR "inverted"
+}