[LLVMdev] Cross-Block Dead Store Elimination

[Balaram Makam]

http://llvm.org/bugs/show_bug.cgi?id=5625

 

Thanks,

Balaram

 

From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
Behalf Of Philip Reames
Sent: Wednesday, November 05, 2014 7:48 PM
To: Artem Dinaburg; llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] Cross-Block Dead Store Elimination

 

 

On 10/24/2014 01:17 PM, Artem Dinaburg wrote:

Hi,
 
It looks like the DeadStoreElimination optimization doesn't work across
BasicBlock boundaries. The project I'm working on
(https://github.com/trailofbits/mcsema), would tremendously benefit from
even simple cross-block DSE. 

If you have specific small examples which aren't getting caught, I'd be
interested in seeing test cases (as bugs.) 

There was a patch to do non-local DSE few years ago
(http://lists.cs.uiuc.edu/pipermail/llvmdev/2010-January/028751.html), but
seems that the patch was never merged.
 
Is there an existing way to do cross-block DSE?

EarlyCSE handles limited cases here.  GVN probably could, but doesn't seem
to.  (Which surprises me.)



Was there something wrong with the original non-local DSE patch that it
wasn't merged?

I suspect it got lost in review.  It looks like there were some quality
issues with the original implementation and the cycle never got closed.



 
 
Thanks,
Artem






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