On Tue, 30 Aug 2011, Richard Guenther wrote:
>
> I've run into PR48571 again, and after having fun with out data-dep
> analysis code I indeed believe that we should not try to re-construct
> ARRAY_REFs from code involving pointer arithmetic. ARRAY_REFs
> have constraints imposed on them that are relied on by data dependence
> analysis and that are indeed useful to have (the index is within
> bounds, otherwise undefined behavior). We can't recover from
> lowering that happened, much as Zdenek argued when I initially
> proposed to lower all ARRAY_REFs to pointer arithmetic with the
> original MEM_REF design.
>
> Thus, the following completes the partial removal of reference
> re-constructing I did when merging MEM_REFs (I removed the code
> re-constructing COMPONENT_REFs back then).
>
> Not much fallout, much to my surprise (I've tried it initially
> on the MEM_REF branch, but quickly gave up on this additional task).
> We've appearantly become better in handling of pointer based accesses
> (we've already much experience here with GFortran lowering
> multi-dimensional array accesses to one-dimensional ones).
>
> The patch XFAILs one -Warray-bounds testcase, the -Warray-bounds
> infrastructure needs some serious TLC which I didn't want to fold
> into this patch. The testcase in question also really asks for
> an 'access outside of object' warning, similar to the
> 'offset outside bounds of constant string' one we have.
>
> Bootstrapped and tested an earlier version on x86_64-unknown-linux-gnu,
> a final bootstrap and regtest cycle is currently running.
>
> (yes, there are still
> tree-ssa-forwprop.c:forward_propagate_addr_into_variable_array_index and
> fold-const.c:try_move_mult_to_index)
Actually I forgot
* gcc.dg/tree-ssa/ssa-ccp-25.c: Remove.
* gcc.dg/tree-ssa/ssa-ccp-26.c: Likewise.
which are feature tests for the reconstruction. Likewise I missed
a recalculate_side_effects (*expr_p) in POINTER_PLUS_EXPR gimplification.
With both fixed, bootstrapped and tested on x86_64-unknown-linxu-gnu
and applied to trunk.
Richard.
