[llvm-commits] More aggressive speculation in SimplifyCFG

[Krzysztof Parzyszek]

On 1/22/2013 5:55 PM, Evan Cheng wrote:
>
> What are you trying to accomplish with this change? It's hard to reason about the cost effectiveness of select formation in LLVM IR. Have you looked at the EarlyIfConversion pass?

This was written almost a year ago.  I don't know if the 
early-if-conversion existed then, and if it did, then I was unaware of 
it.  This was mainly motivated by source code analysis in the benchmarks 
that we were working on at the time.  The main thing was to linearize 
the control flow, specifically to eliminate small blocks, even if it 
comes at the price of speculatively executing some code.
Cost effectiveness is definitely tricky---I don't know how this could be 
made universally applicable to every target.

The reason I'm submitting it is basically that we have it, it works for 
us, and maybe someone would find it useful.  I haven't analyzed the 
early if conversion, so I'm not sure how this code compares to it.

-Krzysztof

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