[PATCH] D72225: Align branches within 32-Byte boundary(Prefix padding)

Mon Jan 13 12:09:27 PST 2020

MaskRay added a comment.

In D72225#1816594 <https://reviews.llvm.org/D72225#1816594>, @LuoYuanke wrote:

> The patch LGTM. I'd like to see the patch land before the llvm release.

We can play it safe. NOP padding is available which should achieve most of the mitigation benefits (http://lists.llvm.org/pipermail/llvm-dev/2019-December/137610.html hw vs hw_sw_nop). This patch retrieves a bit more performance loss back at the risk of some more uncertainty. I can remove `-mllvm -x86-align-branch-prefix-size=` from D72463 <https://reviews.llvm.org/D72463> and commit it (if it gets approved) before the 10.0.0 branch date (2020-01-15). We should definitely speed up reviewing this patch and make it available soon, so that downstream users playing with -mbranches-within-32B-boundaries.

> If you have interest in designing such an interface for MCObjectStreamer and placing the logic in one place, you can reimplement the Prefix Padding after the patch is landed, I will be very glad to help you review that patch.

Thanks. I'll definitely think more in this area.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72225/new/

https://reviews.llvm.org/D72225