Re: [PATCH] Fix arrays in rtx.u + add minor rtx verification

[Jakub Jelinek <jakub at redhat dot com>]

On Fri, Jun 20, 2014 at 01:55:41PM -0600, Jeff Law wrote:
> >like spot.  Most RTLs are allocated through rtx_alloc and the size
> >is determined from RTX_HDR_SIZE (i.e. offsetof) and/or RTX_CODE_SIZE,
> >so your rtl.h change IMHO shouldn't affect anything but make the
> >expmed.c init_expmed_rtl structure somewhat longer.
> Right.  This comment was actually very helpful in that I wasn't aware of
> precisely which cases Marek was trying to address.
> 
> Presumably the [1] sizing is what prevents any compile-time checking of
> this?

First version of Marek's patch did that (never instrumented [], [0] and
[1] arrays, no matter where they appeared, and instrumented everything
else).
Latest patch only never instruments [] (which, by definition can only
appear at the end of structure), other arrays (no matter what size)
aren't instrumented if they aren't followed by any fields, or
if the base of the handled components is not INDIRECT_REF/MEM_REF
(so, typically is a decl).
u.fld[1] array is the last field, so we don't warn for that, but when
rtx_def appears in another structure (in expmed.c) or if e.g. even
some code had a rtx_def typed variable and accessed say u.fld[1] in there,
it would be instrumented.

Whether we should have a strict array bounds mode where we would instrument
even arrays at the end of structures (with the exception of []) is something
to be discussed.

	Jakub