Revert of AVX 2 SrcOver blits: color32, blitmask.

src/opts/SkOpts_avx2.cpp

-/*
- * Copyright 2015 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#include "SkOpts.h"
-#define SK_OPTS_NS sk_avx2
-
-#ifndef SK_SUPPORT_LEGACY_X86_BLITS
-
-namespace sk_avx2 {
-
-// AVX2 has masked loads and stores.  We'll use them for N<4 pixels.
-static __m128i mask(int n) {
-    static const int masks[][4] = {
-        { 0, 0, 0, 0},
-        {~0, 0, 0, 0},
-        {~0,~0, 0, 0},
-        {~0,~0,~0, 0},
-    };
-    return _mm_load_si128((const __m128i*)masks+n);
-}
-
-// Load 8, 4, or 1-3 constant pixels or coverages (4x replicated).
-static __m256i next8(    uint32_t val) { return _mm256_set1_epi32(val); }
-static __m128i next4(    uint32_t val) { return    _mm_set1_epi32(val); }
-static __m128i tail(int, uint32_t val) { return    _mm_set1_epi32(val); }
-
-static __m256i next8(    uint8_t val) { return _mm256_set1_epi8(val); }
-static __m128i next4(    uint8_t val) { return    _mm_set1_epi8(val); }
-static __m128i tail(int, uint8_t val) { return    _mm_set1_epi8(val); }
-
-// Load 8, 4, or 1-3 variable pixels or coverages (4x replicated).
-// next8() and next4() increment their pointer past what they just read.  tail() doesn't bother.
-static __m256i next8(const uint32_t*& ptr) {
-    auto r = _mm256_loadu_si256((const __m256i*)ptr);
-    ptr += 8;
-    return r;
-}
-static __m128i next4(const uint32_t*& ptr) {
-    auto r = _mm_loadu_si128((const __m128i*)ptr);
-    ptr += 4;
-    return r;
-}
-static __m128i tail(int n, const uint32_t* ptr) {
-    return _mm_maskload_epi32((const int*)ptr, mask(n));
-}
-
-static __m256i next8(const uint8_t*& ptr) {
-    auto r = _mm256_cvtepu8_epi32(_mm_loadl_epi64((const __m128i*)ptr));
-    r = _mm256_shuffle_epi8(r, _mm256_setr_epi8(0,0,0,0, 4,4,4,4, 8,8,8,8, 12,12,12,12,
-                                                0,0,0,0, 4,4,4,4, 8,8,8,8, 12,12,12,12));
-    ptr += 8;
-    return r;
-}
-static __m128i next4(const uint8_t*& ptr) {
-    auto r = _mm_shuffle_epi8(_mm_cvtsi32_si128(*(const uint32_t*)ptr),
-                              _mm_setr_epi8(0,0,0,0, 1,1,1,1, 2,2,2,2, 3,3,3,3));
-    ptr += 4;
-    return r;
-}
-static __m128i tail(int n, const uint8_t* ptr) {
-    uint32_t x = 0;
-    switch (n) {
-        case 3: x |= (uint32_t)ptr[2] << 16;
-        case 2: x |= (uint32_t)ptr[1] <<  8;
-        case 1: x |= (uint32_t)ptr[0] <<  0;
-    }
-    auto p = (const uint8_t*)&x;
-    return next4(p);
-}
-
-// For i = 0...n, tgt = fn(dst,src,cov), where Dst,Src,and Cov can be constants or arrays.
-template <typename Dst, typename Src, typename Cov, typename Fn>
-static void loop(int n, uint32_t* t, const Dst dst, const Src src, const Cov cov, Fn&& fn) {
-    // We don't want to muck with the callers' pointers, so we make them const and copy here.
-    Dst d = dst;
-    Src s = src;
-    Cov c = cov;
-
-    // Writing this as a single while-loop helps hoist loop invariants from fn.
-    while (n) {
-        if (n >= 8) {
-            _mm256_storeu_si256((__m256i*)t, fn(next8(d), next8(s), next8(c)));
-            t += 8;
-            n -= 8;
-            continue;
-        }
-        if (n >= 4) {
-            _mm_storeu_si128((__m128i*)t, fn(next4(d), next4(s), next4(c)));
-            t += 4;
-            n -= 4;
-        }
-        if (n) {
-            _mm_maskstore_epi32((int*)t, mask(n), fn(tail(n,d), tail(n,s), tail(n,c)));
-        }
-        return;
-    }
-}
-
-//                                       packed                                              //
-// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ //
-//                                      unpacked                                             //
-
-// Everything on the packed side of the squiggly line deals with densely packed 8-bit data,
-// e.g [ BGRA bgra ... ] for pixels or [ CCCC cccc ... ] for coverage.
-//
-// Everything on the unpacked side of the squiggly line deals with unpacked 8-bit data,
-// e.g. [ B_G_ R_A_ b_g_ r_a_ ... ] for pixels or [ C_C_ C_C_ c_c_ c_c_ ... ] for coverage,
-// where _ is a zero byte.
-//
-// Adapt<Fn> / adapt(fn) allow the two sides to interoperate,
-// by unpacking arguments, calling fn, then packing the results.
-//
-// This lets us write most of our code in terms of unpacked inputs (considerably simpler)
-// and all the packing and unpacking is handled automatically.
-
-template <typename Fn>
-struct Adapt {
-    Fn fn;
-
-    __m256i operator()(__m256i d, __m256i s, __m256i c) {
-        auto lo = [](__m256i x) { return _mm256_unpacklo_epi8(x, _mm256_setzero_si256()); };
-        auto hi = [](__m256i x) { return _mm256_unpackhi_epi8(x, _mm256_setzero_si256()); };
-        return _mm256_packus_epi16(fn(lo(d), lo(s), lo(c)),
-                                   fn(hi(d), hi(s), hi(c)));
-    }
-
-    __m128i operator()(__m128i d, __m128i s, __m128i c) {
-        auto unpack = [](__m128i x) { return _mm256_cvtepu8_epi16(x); };
-        auto   pack = [](__m256i x) {
-            auto x01 = x,
-                 x23 = _mm256_permute4x64_epi64(x, 0xe);  // 0b1110
-            return _mm256_castsi256_si128(_mm256_packus_epi16(x01, x23));
-        };
-        return pack(fn(unpack(d), unpack(s), unpack(c)));
-    }
-};
-
-template <typename Fn>
-static Adapt<Fn> adapt(Fn&& fn) { return { fn }; }
-
-// These helpers all work exclusively with unpacked 8-bit values,
-// except div255() which is 16-bit -> unpacked 8-bit, and mul255() which is the reverse.
-
-// Divide by 255 with rounding.
-// (x+127)/255 == ((x+128)*257)>>16.
-// Sometimes we can be more efficient by breaking this into two parts.
-static __m256i div255_part1(__m256i x) { return _mm256_add_epi16  (x, _mm256_set1_epi16(128)); }
-static __m256i div255_part2(__m256i x) { return _mm256_mulhi_epu16(x, _mm256_set1_epi16(257)); }
-static __m256i div255(__m256i x) { return div255_part2(div255_part1(x)); }
-
-// (x*y+127)/255, a byte multiply.
-static __m256i scale(__m256i x, __m256i y) { return div255(_mm256_mullo_epi16(x, y)); }
-
-// (255 * x).
-static __m256i mul255(__m256i x) { return _mm256_sub_epi16(_mm256_slli_epi16(x, 8), x); }
-
-// (255 - x).
-static __m256i inv(__m256i x) { return _mm256_xor_si256(_mm256_set1_epi16(0x00ff), x); }
-
-// ARGB argb ... -> AAAA aaaa ...
-static __m256i alphas(__m256i px) {
-    const int a = 2 * (SK_A32_SHIFT/8);  // SK_A32_SHIFT is typically 24, so this is typically 6.
-    const int _ = ~0;
-    return _mm256_shuffle_epi8(px, _mm256_setr_epi8(a+0,_,a+0,_,a+0,_,a+0,_,
-                                                    a+8,_,a+8,_,a+8,_,a+8,_,
-                                                    a+0,_,a+0,_,a+0,_,a+0,_,
-                                                    a+8,_,a+8,_,a+8,_,a+8,_));
-}
-
-
-// SrcOver, with a constant source and full coverage.
-static void blit_row_color32(SkPMColor* tgt, const SkPMColor* dst, int n, SkPMColor src) {
-    // We want to calculate s + (d * inv(alphas(s)) + 127)/255.
-    // We'd generally do that div255 as s + ((d * inv(alphas(s)) + 128)*257)>>16.
-
-    // But we can go one step further to ((s*255 + 128 + d*inv(alphas(s)))*257)>>16.
-    // This lets us hoist (s*255+128) and inv(alphas(s)) out of the loop.
-    auto s = _mm256_cvtepu8_epi16(_mm_set1_epi32(src)),
-         s_255_128 = div255_part1(mul255(s)),
-         A = inv(alphas(s));
-
-    const uint8_t cov = 0xff;
-    loop(n, tgt, dst, src, cov, adapt([=](__m256i d, __m256i, __m256i) {
-        return div255_part2(_mm256_add_epi16(s_255_128, _mm256_mullo_epi16(d, A)));
-    }));
-}
-
-// SrcOver, with a constant source and variable coverage.
-// If the source is opaque, SrcOver becomes Src.
-static void blit_mask_d32_a8(SkPMColor* dst,     size_t dstRB,
-                             const SkAlpha* cov, size_t covRB,
-                             SkColor color, int w, int h) {
-    if (SkColorGetA(color) == 0xFF) {
-        const SkPMColor src = SkSwizzle_BGRA_to_PMColor(color);
-        while (h --> 0) {
-            loop(w, dst, (const SkPMColor*)dst, src, cov,
-                    adapt([](__m256i d, __m256i s, __m256i c) {
-                // Src blend mode: a simple lerp from d to s by c.
-                // TODO: try a pmaddubsw version?
-                return div255(_mm256_add_epi16(_mm256_mullo_epi16(inv(c),d),
-                                               _mm256_mullo_epi16(    c ,s)));
-            }));
-            dst += dstRB / sizeof(*dst);
-            cov += covRB / sizeof(*cov);
-        }
-    } else {
-        const SkPMColor src = SkPreMultiplyColor(color);
-        while (h --> 0) {
-            loop(w, dst, (const SkPMColor*)dst, src, cov,
-                    adapt([](__m256i d, __m256i s, __m256i c) {
-                // SrcOver blend mode, with coverage folded into source alpha.
-                auto sc = scale(s,c),
-                     AC = inv(alphas(sc));
-                return _mm256_add_epi16(sc, scale(d,AC));
-            }));
-            dst += dstRB / sizeof(*dst);
-            cov += covRB / sizeof(*cov);
-        }
-    }
-}
-
-}  // namespace sk_avx2
-
-#endif
-
-namespace SkOpts {
-    void Init_avx2() {
-    #ifndef SK_SUPPORT_LEGACY_X86_BLITS
-        blit_row_color32 = sk_avx2::blit_row_color32;
-        blit_mask_d32_a8 = sk_avx2::blit_mask_d32_a8;
-    #endif
-    }
-}