[llvm-dev] Conditional analysis before inliner

[Friedman, Eli via llvm-dev]

On 4/19/2018 1:57 PM, Anom LLVM via llvm-dev wrote:
> Hi,
>
> I have pass phase ordering question.
>
> I am interested in performing a transformation that matches several 
> LLVM IR instructions and converts them to a single builtin. This sort 
> of transformation must occur prior to inlining because inlining needs 
> to analyze cost of the builtin. However, the LLVM IR -> builtin 
> transformation requires scalar evolution which typically doesn't run 
> until after the inliner.

This isn't right, or at least, not the complete picture; loop 
optimization passes run interleaved with the inliner.  (Try looking at 
the output of "-debug-pass=Executions" to see exactly what's happening.)

> My question is, is there a way to run scalar evolution conditionally 
> prior to inlining? I'd like to leave compile time unaffected if my 
> code doesn't contain any of these builtins.

ScalarEvolution is lazy, so it's essentially free if you don't query it.

-Eli

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project