[PATCH] D79155: [CodeGen] Increase applicability of ffine-grained-bitfield-accesses for targets with limited native integer widths

[Dave Green via Phabricator via cfe-commits]

dmgreen added a comment.

Hello. We've received reports that this is bloating codesize of some code, quite a lot in places. There is an example in https://godbolt.org/z/66TEKa1xK. Essentially the glomming together of reads/writes into i32's (in our case) helps to reduce the total number of loads/stores needed. Splitting that up into individual i8/i16's creates a lot more load/mask/load/mask/or/store sequences.

I suspect it's better in cases, worse in others. It depends on where exactly the bitfield delimitators lie. And whether they are more likely to be on i32/i64 boundaries (which I believe is common in a lot of cases bitfields are used in), or to be more randomly distributed.


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https://reviews.llvm.org/D79155