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Re: prevent optimisation of variables on SSA

From: Diego Novillo <dnovillo at google dot com>
To: Martin Schindewolf <schindew at ira dot uka dot de>
Cc: gcc at gcc dot gnu dot org, Albert Cohen <Albert dot Cohen at inria dot fr>
Date: Tue, 19 Aug 2008 08:38:13 -0400
Subject: Re: prevent optimisation of variables on SSA
References: <48A5B643.4060306@ira.uka.de>

On 8/15/08 1:00 PM, Martin Schindewolf wrote:

Hi all,

I currently introduce a temporary variable on SSA form but it
does not survive the SSA optimisation passes. (Not even the
simple ones triggered with -O1). Since the temporary variable
is considered to be a gimple register it is not possible to
set a VUSE or VDEF for it. (I tried and it breaks the SSA
properties). Are there any mechanisms to work around this
restriction and set the VDEF/VUSE anyway or is there a way to
tell the SSA optimisers not to touch this variable (or
SSA_NAME)?
Thank you very much for sharing your thoughts!

You are not providing enough information. Is the creating assignment for the new SSA variable dead? If there are no uses of your new variable, then DCE will remove the assignment.

Diego.

References:
- prevent optimisation of variables on SSA
  - From: Martin Schindewolf

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