From: law@redhat.com
To: Zdenek Dvorak <rakdver@atrey.karlin.mff.cuni.cz>
Cc: gcc@gcc.gnu.org
Subject: Re: [tree-ssa] Kills by VDEFs in mark_def_sites
Date: Fri, 30 Apr 2004 22:55:00 -0000 [thread overview]
Message-ID: <200404302131.i3ULVXXo016140@speedy.slc.redhat.com> (raw)
In-Reply-To: Your message of "Wed, 14 Apr 2004 23:36:04 +0200." <20040414213604.GA32480@atrey.karlin.mff.cuni.cz>
In message <20040414213604.GA32480@atrey.karlin.mff.cuni.cz>, Zdenek Dvorak wri
tes:
>Hello,
>
>a comment in tree-into-ssa.c:mark_def_sites states that
>
>/* Note that virtual definitions are irrelevant for computing KILLS
> because a VDEF does not constitute a killing definition of the
> variable. */
>
>and indeed, we do not set a bit in "kills" bitmap for VDEFs.
>
>There are two things that make this part of code a bit weird:
>
>1) For operand of VDEF and for VUSE we test whether the bit is set
> in the "kills" bitmap; however this is clearly useless, as there
> is no way how there could be anything set in this bitmap for virtual
> operands.
>
>2) The comment above is moreorless useless as well. Even if we set the
> bit in the "kills" bitmap, everything would work exactly the same
> way, since VDEF has an operand that is processed before the VDEF's
> result, so the basic block processed would be marked in the livein
> bitmap as well.
>
>Are these observations correct, or am I missing something?
I believe your observations are correct. I believe this code only made
sense in the world where we still mixed real and virtual operands in
strange and not so wonderful ways.
I'll give things a spin with the kills bitmap gunk removed for virtuals.
jeff
prev parent reply other threads:[~2004-04-30 21:31 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-04-14 22:04 Zdenek Dvorak
2004-04-30 22:55 ` law [this message]
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