[PATCH] Allow the RegisterCoalescer to remove copies to reserved registers

[Quentin Colombet]

Hi Hal,

I am worry about the approach here.
With this approach, we are propagating constraints on the allocation problem that we cannot recover from. We cannot split physical register live-ranges. The bottom line is it may introduce more spilling or more expensive splitting.

I would suggest instead to extend the copy propagation pass to handle such cases, since at that time the allocation has all been done. IIRC the copy propagation pass is top down, but we may be able to add a bottom up pass that would catch this.

What do you think?

Cheers,
-Quentin


http://reviews.llvm.org/D6978

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