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Re: GCSE store motion
- From: David Edelsohn <dje at watson dot ibm dot com>
- To: Roger Sayle <roger at eyesopen dot com>
- Cc: Daniel Berlin <dberlin at dberlin dot org>, gcc at gcc dot gnu dot org, Mark Mitchell <mark at codesourcery dot com>
- Date: Wed, 15 May 2002 13:17:40 -0400
- Subject: Re: GCSE store motion
>>>>> Roger Sayle writes:
Roger> I apologise profusely. I'm not arguing that store motion is
Roger> useful or shouldn't be disabled per se, just that store motion
Roger> probably isn't broken without any evidence to the contrary.
Roger> I don't want Mark or any other MAINTAINER disabling it just on
Roger> the mistaken understanding that it was causing regressions.
The lack of regressions does not mean that the implementation of
store motion is correct. Given that the current implementation of store
motion generally does not move any stores, it is even more difficult to
create a testcase which shows how store motion may produce incorrect code.
I personally think that this argues *for* disabling it by default because
we do not have a coverage tool to ensure that the specific optimization is
Daniel performed an analysis of the store motion implementation
itself and he believes that he found an error (a reversed condition, if I
remember correctly). Given that we cannot test GCSE store motion
directly, I think it is best to leave it disabled by default until store
motion is fixed or someone finds a flaw in Daniel's analysis.