code review 6783054: cmd/gc: do simple bounds checking of constant indices/s...

cmd/gc: do simple bounds checking of constant indices/slices in typecheck.

This should make the compiler emit errors specific to the bounds checking instead of overflow errors on the underlying types.

Updates issue 4232.

[DMorsing, 2012-10-26 20:05:20]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://code.google.com/p/go/

[rsc, 2012-11-01 16:54:25]

Thanks for working on this.

https://codereview.appspot.com/6783054/diff/1002/src/cmd/gc/typecheck.c
File src/cmd/gc/typecheck.c (right):

https://codereview.appspot.com/6783054/diff/1002/src/cmd/gc/typecheck.c#newco...
src/cmd/gc/typecheck.c:827: yyerror("slice/array index must be non-negative");
This message disagrees in form with the message at lines 924 and 934. Could you
use that form here?

https://codereview.appspot.com/6783054/diff/1002/src/cmd/gc/typecheck.c#newco...
src/cmd/gc/typecheck.c:829: yyerror("array index out of bounds");
Same idea.
invalid array index %N (out of bounds for %d-element array)
or something like that

[DMorsing, 2012-11-01 17:13:32]

Hello rsc@golang.org (cc: golang-dev@googlegroups.com),

Please take another look.

[DMorsing, 2012-11-01 17:14:41]

Whoops, a bit too fast on the trigger.

Anyway, both suggestions done.

[rsc, 2012-11-01 17:24:11]

LGTM

https://codereview.appspot.com/6783054/diff/9001/src/cmd/gc/typecheck.c
File src/cmd/gc/typecheck.c (right):

https://codereview.appspot.com/6783054/diff/9001/src/cmd/gc/typecheck.c#newco...
src/cmd/gc/typecheck.c:827: yyerror("invalid array/slice index %N (index must be
non-negative)", n->right);
Since we're cleaning things up, please use the right word here instead of
array/slice.

[DMorsing, 2012-11-01 17:45:26]

*** Submitted as http://code.google.com/p/go/source/detail?r=da736dff5c27 ***

cmd/gc: do simple bounds checking of constant indices/slices in typecheck.

This should make the compiler emit errors specific to the bounds checking
instead of overflow errors on the underlying types.

Updates issue 4232.

R=rsc
CC=golang-dev
http://codereview.appspot.com/6783054