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Re: [RFC] Fix PR28684
- From: Geert Bosch <bosch at adacore dot com>
- To: Revital1 Eres <ERES at il dot ibm dot com>
- Cc: Richard Guenther <rguenther at suse dot de>, Ayal Zaks <ZAKS at il dot ibm dot com>, Dorit Nuzman <DORIT at il dot ibm dot com>, gcc-patches at gcc dot gnu dot org, roger at eyesopen dot com, Clint Whaley <whaley at cs dot utsa dot edu>
- Date: Thu, 16 Nov 2006 11:09:36 -0500
- Subject: Re: [RFC] Fix PR28684
- References: <OFE1314467.33CACBB1-ONC2257228.004F50A8-C2257228.004F6098@il.ibm.com>
On Nov 16, 2006, at 09:30, Revital1 Eres wrote:
I believe we may also inhibit or create underflow or overflow with
re-ordering for example
(X + C1) - C2 to X + (C1 - C2)
for X near FLT_MAX and C1 sufficiently large.
Right.
Even transforming
X + Y - Y to X
may fail to propagate a NaN Y to the result.
Is transforming X + Y - Y to X is allowed by our flag?
Isn't it like x * 0 -> 0?
It seems we really need a table with a row for each transformation,
and columns indicating which flags allow or inhibit the compiler
to perform the transformation. Shall I start such a page on the Wiki?
When we converge to a list that people can agree with, this would
then be moved to the regular documentation.
-Geert