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Re: Question about how to fix PR69052
- From: "Bin.Cheng" <amker dot cheng at gmail dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Tue, 26 Jan 2016 16:36:45 +0000
- Subject: Re: Question about how to fix PR69052
- Authentication-results: sourceware.org; auth=none
- References: <CAHFci280ObgaSxzCBiKKBfKONeYsXOue8i84hH=pDwynhC4PNQ at mail dot gmail dot com> <56A67CD9 dot 70405 at redhat dot com> <CAHFci2_=BHm7x3iv9YrFCb=rhrfpmLfH=CQ-=uy7cOyYRDpiwA at mail dot gmail dot com> <56A79E3A dot 7020908 at redhat dot com>
On Tue, Jan 26, 2016 at 4:26 PM, Jeff Law <email@example.com> wrote:
> On 01/26/2016 02:28 AM, Bin.Cheng wrote:
>> Yes, loop invariant now increased invariant cost if the invariant
>> can't be propagated into address expression. Problem is we check
>> propagation by simply replacing use with def in memory reference then
>> verifying result insn with verify_changes. Apparently more advanced
>> transforms are necessary, just like what combine does.
>> I am surprised that rtl_fwprop_addr doesn't handle this either, it's
>> an exact address expression propagation example.
> So the question now becomes whether or not the work done by combine.c is
> dependent on knowledge that is specific to combine or is it just a series of
> transformations that we could make available (preferably moving it to
> If we can factor the transformation out and shove it into simplify-rtx, then
> it could be used elsewhere.
According to comment at
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69052#c6, it should be
just re-arrangement of operands, if the comment itself holds.
In this way, the transformation is backend related, maybe better to
keep it in backend, right?