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Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
- From: Richard Henderson <rth at redhat dot com>
- To: Jeff Law <law at redhat dot com>, Jakub Jelinek <jakub at redhat dot com>
- Cc: Jiong Wang <jiong dot wang at arm dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 10 Oct 2014 10:25:47 -0700
- Subject: Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
- Authentication-results: sourceware.org; auth=none
- References: <5429B204 dot 7040200 at arm dot com> <542A2FC5 dot 4020605 at redhat dot com> <542AC02D dot 70508 at arm dot com> <542ADA9D dot 8070709 at redhat dot com> <CAAfDdZ0ti4nfkOL1qTHTtsgpYLCmC5NQcM=_GEBFfJHpcx+XCw at mail dot gmail dot com> <543558B8 dot 3060006 at arm dot com> <54380267 dot 8030705 at redhat dot com> <54380BAF dot 9000602 at arm dot com> <54380ED3 dot 1020203 at redhat dot com> <543810C6 dot 8050104 at redhat dot com> <20141010170408 dot GR10376 at tucnak dot redhat dot com> <54381582 dot 3090404 at redhat dot com>
On 10/10/2014 10:21 AM, Jeff Law wrote:
> On 10/10/14 11:04, Jakub Jelinek wrote:
>> On Fri, Oct 10, 2014 at 11:00:54AM -0600, Jeff Law wrote:
>>> But it's really a lot more like a
>>>> kind of PLUS. If instead we had a LOW to match HIGH it would have been
>>> Right. In fact, I believe at the hardware level it's typically implemented
>>> as addition.
>>
>> Can be addition or bitwise or, as high should have some low bits zero, both
>> usually work the same.
> It can be bitwise-or on some architectures...
Just to be clear, the LOW rtx code I mentioned upthread was for illustration
purposes only. I only intend to change the rtx class of the existing LO_SUM.
:-)
r~