[PATCH] D50924: [CodeGen] add rotate builtins

[Sanjay Patel via Phabricator via cfe-commits]

spatel created this revision.
spatel added reviewers: fabiang, craig.topper, rnk, thakis.
Herald added a subscriber: mcrosier.

This exposes the LLVM funnel shift intrinsics as more familiar bit rotation functions in clang (when both halves of a funnel shift are the same value, it's a rotate).

I think we're free to name these as we want because we're not copying gcc, but if there's some other existing art that we want to replicate, let me know.

The funnel shift intrinsics were added here:
https://reviews.llvm.org/D49242

With improved codegen in:
https://reviews.llvm.org/rL337966
https://reviews.llvm.org/rL339359

And basic IR optimization added in:
https://reviews.llvm.org/rL338218
https://reviews.llvm.org/rL340022

...so I think these should produce asm output that's equal or better to the multi-instruction alternatives using primitive C/IR ops.

In the motivating loop example from PR37387:
https://bugs.llvm.org/show_bug.cgi?id=37387#c7
...we get the expected 'rolq' x86 instructions if we substitute the rotate builtin into the source.


https://reviews.llvm.org/D50924

Files:
  docs/LanguageExtensions.rst
  include/clang/Basic/Builtins.def
  lib/CodeGen/CGBuiltin.cpp
  test/CodeGen/builtin-rotate.c

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