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Re: [PATCH PR62151]Fix uninitialized register issue caused by distribute_notes in combine pass
- From: Segher Boessenkool <segher at kernel dot crashing dot org>
- To: Jeff Law <law at redhat dot com>
- Cc: "Bin.Cheng" <amker dot cheng at gmail dot com>, Richard Earnshaw <rearnsha at arm dot com>, Bin Cheng <bin dot cheng at arm dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Date: Sun, 31 Aug 2014 07:18:44 -0500
- Subject: Re: [PATCH PR62151]Fix uninitialized register issue caused by distribute_notes in combine pass
- Authentication-results: sourceware.org; auth=none
- References: <000a01cfc1de$cac1c230$60454690$ at arm dot com> <53FDB440 dot 5030904 at arm dot com> <CAHFci28BS75pySKVtLTeY8BQsYupJHvXs73ZdYq1RkfHLbXocQ at mail dot gmail dot com> <5401680D dot 60907 at redhat dot com>
On Fri, Aug 29, 2014 at 11:58:37PM -0600, Jeff Law wrote:
> One could argue that this mess is a result of trying to optimize a reg
> that is set more than once. Though I guess that might be a bit of a
> big hammer.
It works fine in other cases, and is quite beneficial for e.g. optimising
instruction sequences that set a fixed carry register twice.
In the testcase (and comment in the proposed patch), why is combine
combining four insns at all? That means it rejected combining just the
first three. Why did it do that?
Segher