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Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer

From: Jeff Law <law at redhat dot com>
To: Richard Henderson <rth 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 11:26:39 -0600
Subject: Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
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On 10/10/14 11:25, Richard Henderson wrote:

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.

That was my expectation :-)
jeff

References:
- Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
  - From: Jiong Wang
- Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
  - From: Richard Henderson
- Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
  - From: Jiong Wang
- Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
  - From: Richard Henderson
- Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
  - From: Jeff Law
- Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
  - From: Jakub Jelinek
- Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
  - From: Jeff Law
- Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer
  - From: Richard Henderson

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