r254251 - ARM v8.1a adds Advanced SIMD instructions for Rounding Double Multiply

[Tim Northover via cfe-commits]

On 1 December 2015 at 10:42, James Molloy via cfe-commits
<cfe-commits at lists.llvm.org> wrote:
> W.r.t the test-suite, that is a possibility. There are currently no
> codegen-filecheck tests in the test-suite but there seems to be no reason I
> can see why not. The disadvantage there for me is that we take short
> running, simple tests and demote them to be run less often.

Compared to test-suite these are short-running. But compared to
virtually everything else in check-all they're beasts.

I've been meaning to do *something* about them for a long while.
They're not even particularly good: these days they're a huge
hand-written mess and they don't test data flow at all.

Given how the code is actually generated, it would be absurdly easy to
accidentally feed LHS into an LLVM instruction twice by mistake. For a
long while we randomly flipped the operand order in vfma_lane_* on
Darwin, and had to phase that out gradually.

Unfortunately, I haven't actually come up with a better replacement.
Even if we could magically replace each one with a test of LLVM IR I
don't think it would improve things massively.

Tim.