SkPMFloat: avoid loads and stores where possible.

A store/load pair like this is a redundant no-op:
  store simd_register_a, memory_address
  load  memory_address, simd_register_a

Everyone seems to be good at removing those when using SSE, but GCC and Clang
are pretty terrible at this for NEON.  We end up issuing both redundant
commands, usually to and from the stack.  That's slow.  Let's not do that.

This CL unions in the native SIMD register type into SkPMFloat, so that we can
assign to and from it directly, which is generating a lot better NEON code.  On
my Nexus 5, the benchmarks improve from 36ns to 23ns.

SSE is just as fast either way, but I paralleled the NEON code for consistency.
It's a little terser.  And because it needed the platform headers anyway, I
moved all includes into SkPMFloat.h, again only for consistency.

I'd union in Sk4f too to make its conversion methods a little clearer,
but MSVC won't let me (it has a copy constructor... they're apparently not up
to speed with C++11 unrestricted unions).

BUG=skia:

Review URL: https://codereview.chromium.org/1015083004

1 files changed, 7 insertions, 5 deletions

diff --git a/src/opts/SkPMFloat_neon.h b/src/opts/SkPMFloat_neon.h
index 036d10d0d6..6c9df37e51 100644
--- a/src/opts/SkPMFloat_neon.h
+++ b/src/opts/SkPMFloat_neon.h
@@ -1,5 +1,7 @@
-#include "SkColorPriv.h"
-#include <arm_neon.h>
+inline SkPMFloat& SkPMFloat::operator=(const SkPMFloat& that) {
+    fColors = that.fColors;
+    return *this;
+}
 
 // For SkPMFloat(SkPMFColor), we widen our 8 bit components (fix8) to 8-bit components in 16 bits
 // (fix8_16), then widen those to 8-bit-in-32-bits (fix8_32), and finally convert those to floats.
@@ -13,13 +15,13 @@ inline SkPMFloat::SkPMFloat(SkPMColor c) {
     uint8x8_t   fix8    = (uint8x8_t)vdup_n_u32(c);
     uint16x8_t  fix8_16 = vmovl_u8(fix8);
     uint32x4_t  fix8_32 = vmovl_u16(vget_low_u16(fix8_16));
-    vst1q_f32(fColor, vcvtq_f32_u32(fix8_32));
+    fColors = vcvtq_f32_u32(fix8_32);
     SkASSERT(this->isValid());
 }
 
 inline SkPMColor SkPMFloat::get() const {
     SkASSERT(this->isValid());
-    float32x4_t add_half = vaddq_f32(vld1q_f32(fColor), vdupq_n_f32(0.5f));
+    float32x4_t add_half = vaddq_f32(fColors, vdupq_n_f32(0.5f));
     uint32x4_t  fix8_32  = vcvtq_u32_f32(add_half);  // vcvtq_u32_f32 truncates, so round manually
     uint16x4_t  fix8_16  = vmovn_u32(fix8_32);
     uint8x8_t   fix8     = vmovn_u16(vcombine_u16(fix8_16, vdup_n_u16(0)));
@@ -29,7 +31,7 @@ inline SkPMColor SkPMFloat::get() const {
 }
 
 inline SkPMColor SkPMFloat::clamped() const {
-    float32x4_t add_half = vaddq_f32(vld1q_f32(fColor), vdupq_n_f32(0.5f));
+    float32x4_t add_half = vaddq_f32(fColors, vdupq_n_f32(0.5f));
     uint32x4_t  fix8_32  = vcvtq_u32_f32(add_half);  // vcvtq_u32_f32 truncates, so round manually
     uint16x4_t  fix8_16  = vqmovn_u32(fix8_32);
     uint8x8_t   fix8     = vqmovn_u16(vcombine_u16(fix8_16, vdup_n_u16(0)));