[llvm-commits] [PATCH] Bug fix to enable zextload on targets that support it

[Mishne, Alon]

Hi Silviu,

Thanks for letting me know, I didn't understand the loop is actually required - and you are of course right.
By the way, since the loop is required anyway, I don't really see the benefit of using isConstantSplat() over just anding the lanes (paying in isConstantSplat() time to just decrease AND iterations). But it's a small thing, of course :)

Thanks for correcting me! My patch should not be applied.

-          Alon

From: Silviu Baranga [mailto:silbar01 at arm.com]
Sent: Tuesday, August 28, 2012 11:55
To: Mishne, Alon; llvm-commits at cs.uiuc.edu
Cc: James Molloy
Subject: RE: [llvm-commits] [PATCH] Bug fix to enable zextload on targets that support it

Hi Alon,

I noticed that you are removing the code that ands every lane
of the splat value. That code(the loop) is actually required, since
we might not have the same value for all lanes and we would
still want to fold the AND node.

Related to this, I've sent a patch  a couple of days ago to handle
the same issue:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20120820/148839.html

Cheers,
Silviu


From: llvm-commits-bounces at cs.uiuc.edu<mailto:llvm-commits-bounces at cs.uiuc.edu> [mailto:llvm-commits-bounces at cs.uiuc.edu]<mailto:[mailto:llvm-commits-bounces at cs.uiuc.edu]> On Behalf Of Mishne, Alon
Sent: 26 August 2012 08:27
To: llvm-commits at cs.uiuc.edu<mailto:llvm-commits at cs.uiuc.edu>
Subject: [llvm-commits] [PATCH] Bug fix to enable zextload on targets that support it

Hi,

I've noticed a clever trick in lib/CodeGen/SelectionDAG/DAGCombiner.cpp of identifying an AND whose only purpose is to reset the top bits as a potential zextload instead of extload in targets that support it. However, the code for identifying the constant used in such an AND with a vector is wrong - it makes incorrect usage of the isConstantSplat() method, assuming it works differently from how it really does.

Attached is a patch that fixes this by using that method correctly, enabling a nice optimization on targets that support zextload. The fixed code is also much simpler and more efficient than the incorrect usage, becomes it removes an unneeded loop.

Please review this patch and commit if acceptable,

-          Alon

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