Missing analysis in MCJIT?

[Bader, Aleksey A]

Hi,

It looks like MCJIT::emitObject is missing target specific analysis passes to do efficient code generation.

Codegen runs several preparation passes including Loop Strength Reduction, which hoists some computations out of the loop increasing register pressure, which leads to register spills on 32-bit platform. In order to estimate the profitability of the modification this pass uses TargetTransformInfo analysis data. My understanding is that NoTargetTransformInfo pass is created by default and it is not good enough for efficient code generation. This fix introduces target-specific passes, which provide correct cost of modifications.

Does it make sense?
- Alexey

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