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Re: [PATCH, rtl-optimization]: Fix PR37997: ICE shifting byte to the right with constant > 7FFFFFFF

From: Eric Botcazou <ebotcazou at adacore dot com>
To: Uros Bizjak <ubizjak at gmail dot com>
Cc: "H.J. Lu" <hjl dot tools at gmail dot com>, Richard Henderson <rth at redhat dot com>, gcc-patches at gcc dot gnu dot org
Date: Thu, 10 Sep 2009 16:33:47 +0200
Subject: Re: [PATCH, rtl-optimization]: Fix PR37997: ICE shifting byte to the right with constant > 7FFFFFFF
References: <4AA6785A.80805@gmail.com> <6dc9ffc80909100652s1421e18g9d2b33ef97d1d618@mail.gmail.com> <4AA90BE5.5000209@gmail.com>

> The patch fixes the problem, exposed by unfortunate testcase. The
> problem was that huge CONST_INT didn't satisfy QImode constraints, no
> matter if oldmode was new mode.

You should arrange for not passing QImode as old_mode to convert_modes if 
the input is not valid for QImode.  By breaking the invariant that the 
conversion from mode M to itself is a no-op, you penalize the common case.

-- 
Eric Botcazou

References:
- [PATCH, rtl-optimization]: Fix PR37997: ICE shifting byte to the right with constant > 7FFFFFFF
  - From: Uros Bizjak
- Re: [PATCH, rtl-optimization]: Fix PR37997: ICE shifting byte to the right with constant > 7FFFFFFF
  - From: H.J. Lu
- Re: [PATCH, rtl-optimization]: Fix PR37997: ICE shifting byte to the right with constant > 7FFFFFFF
  - From: Uros Bizjak

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