[PATCH] D30324: [ARM] Thumb2: favor R4-R7 over R12/LR in allocation order when opt for minsize

[Renato Golin via Phabricator via llvm-commits]

rengolin added a comment.

Hi Weiming,

Sorry for the delay. I have two major points with this approach:

1. We're basically selecting different patterns based on different flags by crossing too many wires (table-gen reg definition, sub-target feature, command line option, optimisation flags). Dynamically changing with command line options is going to be harder to test and reproduce user bugs.
2. The benchmark numbers for code size reduction aren't still really *that* encouraging.

Ultimately, having a simple ARM/Thumb1/2 set would be as far as I'd go.

@qcolombet is there some prior art for that kind of fiddling? By looking at the other register files, the most that happens is things like "is64bit", in the same way we have "isThumb1".

cheers,
--renato


https://reviews.llvm.org/D30324