Don't build skein_block_asm.s if we don't have an as binary
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Authored by arichardson on Aug 22 2018, 2:24 PM.

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Reviewers

jhb
brooks
emaste
imp
allanjude

Commits

rS338270: Don't build skein_block_asm.s if we don't have an as binary

Summary

This fixes building libmd on MacOS/Linux. The real fix is probably to
build it as a .S file with $CC instead. It might also be better to just
compile the C file in userspace since the compiler can the use SSE/AVX.

Test Plan

buildworld succeeds without building GNU as.

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Build Status

Buildable 19053
Build 18684: arc lint + arc unit

Event Timeline

arichardson created this revision.Aug 22 2018, 2:24 PM

Harbormaster completed remote builds in B19043: Diff 47098.Aug 22 2018, 2:24 PM

Clang's IAS cannot assemble skein_block_asm.s (D8434) so trying to just use ${CC} instead won't work. LLVM PR 33405 is open to track this.

I think this change is reasonable, although I might suggest adding a comment with more detail, and maybe a .warning if the file exists but we don't have as (e.g. .warning as not available: not using optimized Skein asm

It might be worth spending the time to see how the performance differs. If it's not extreme, then just dropping skein_block_asm.s entirely would make sense given we're talking about an SHA3 candidate that didn't win.

That being said, I see no reason not to commit this version now.

This revision is now accepted and ready to land.Aug 22 2018, 3:55 PM

I wouldn't be surprised if the C version isn't in fact faster with a modern compiler that can use vectorization (SSE/AVX) in userland. The handwritten assembly only uses GPRs.