Re: [PATCH] cleanup gcse.c:canon_modify_mem_list

[Jeff Law <law@redhat.com>]

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On 04/03/11 19:44, Nathan Froyd wrote:
> The patch below converts gcse.c:canon_modify_mem_list to hold VECs
> instead of EXPR_LIST rtxes.  I am ambivalent about the use of VECs in
> canon_modify_mem_list; they will waste some memory compared to the
> linked list scheme present before, though I'm not sure how much.  It
> would depend on the average chain length, etc.  I'm happy to use an
> linked list datastructure instead, allocated out of an
> alloc_pool (better statistics!) or even gcse's private obstack if folks
> think that would be better.  Moving things out of GC memory and
> eliminating a use of EXPR_LIST has to be considered a good thing,
> though...
I've got no strong opinions on all this stuff -- except that blindly
moving stuff out of GC memory isn't necessarily a good thing.  It really
depends on the lifetime of the objects.

Assuming the memory list stuff in gcse doesn't have a lifetime outside
of GCSE and is thus easily tracked, then I've got no fundamental
objection to the change.


> 
> Doing this required addressing an odd little comment in
> record_last_mem_set_info:
> 
>   if (CALL_P (insn))
>     {
>       /* Note that traversals of this loop (other than for free-ing)
> 	 will break after encountering a CALL_INSN.  So, there's no
> 	 need to insert a pair of items, as canon_list_insert does.  */
>       canon_modify_mem_list[bb] =
> 	alloc_INSN_LIST (insn, canon_modify_mem_list[bb]);
>       bitmap_set_bit (blocks_with_calls, bb);
>     }
> 
> This is all well and good, except that the only real traversal of
> canon_modify_mem_list (compute_transp) doesn't check for CALL_INSNs.
It's possible (likely?) the implementation changed over time and the
comment wasn't properly updated.  Unfortunate, but it does happen.


> +  canon_modify_mem_list = GCNEWVEC (VEC(modify_pair,heap) *,
> +				    last_basic_block);
nit; You're missing some whitespace here (after the VEC).

OK.  Please install,

Thanks,
Jeff
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