Reland "Reland "make SkJumper stages normal Skia code""

This is a reland of 78cb579f33943421afc8423a39867fcfd69fed44

This time, lowp stages are controlled by !defined(JUMPER_IS_SCALAR), not
by defined(__clang__).  The two are usually the same, except when we opt
Clang builds into JUMPER_IS_SCALAR artificially.

Some Google3 builds use compilers old enough that they barf when
compiling our NEON code.  It's conceivably also possible to define
JUMPER_IS_SCALAR yourself, but I don't think anyone does that.

Original change's description:
> Reland "make SkJumper stages normal Skia code"
>
> This is a reland of 22e536e3a1a09405d1c0e6f071717a726d86e8d4
>
> Now with fixed #include paths in SkRasterPipeline_opts.h,
> and -ffp-contract=fast for the :hsw target to minimize
> diffs on non-Windows Clang AVX2/AVX-512 bots.
>
> Original change's description:
> > make SkJumper stages normal Skia code
> >
> > Enough clients are using Clang now that we can say, use Clang to build
> > if you want these software pipeline stages to go fast.
> >
> > This lets us drop the offline build aspect of SkJumper stages, instead
> > building as part of Skia using the SkOpts framework.
> >
> > I think everything should work, except I've (temporarily) removed
> > AVX-512 support.  I will put this back in a follow up.
> >
> > I have had to drop Windows down to __vectorcall and our narrower
> > stage calling convention that keeps the d-registers on the stack.
> > I tried forcing sysv_abi, but that crashed Clang.  :/
> >
> > Added a TODO to up the same narrower stage calling convention
> > for lowp stages... we just *don't* today, for no good reason.
> >
> > Change-Id: Iaaa792ffe4deab3508d2dc5d0008c163c24b3383
> > Reviewed-on: https://skia-review.googlesource.com/110641
> > Commit-Queue: Mike Klein <mtklein@chromium.org>
> > Reviewed-by: Herb Derby <herb@google.com>
> > Reviewed-by: Florin Malita <fmalita@chromium.org>
>
> Change-Id: I44f2c03d33958e3807747e40904b6351957dd448
> Reviewed-on: https://skia-review.googlesource.com/112742
> Reviewed-by: Mike Klein <mtklein@chromium.org>

Change-Id: I3d71197d4bbb19ca4a94961a97fa2e54d5cbfb0d
Reviewed-on: https://skia-review.googlesource.com/112744
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/gn/opts.gni b/gn/opts.gni
index 1cc6027af2..34481db3b6 100644
--- a/gn/opts.gni
+++ b/gn/opts.gni
@@ -51,3 +51,4 @@ ssse3 = [
 sse41 = [ "$_src/opts/SkOpts_sse41.cpp" ]
 sse42 = [ "$_src/opts/SkOpts_sse42.cpp" ]
 avx = [ "$_src/opts/SkOpts_avx.cpp" ]
+hsw = [ "$_src/opts/SkOpts_hsw.cpp" ]