From 77aa62c01ed412ddbcc5d02b842a7e2445b51e3e Mon Sep 17 00:00:00 2001
From: mtklein <mtklein@chromium.org>
Date: Tue, 9 Feb 2016 11:03:40 -0800
Subject: [PATCH] Slim down Sk4fRoundtrip benches.

Looks like the conversions are complicated enough to not compile away.
No need to mess with random number generation, etc.
We still need to blackhole it into a volatile in the end.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1682793002

Review URL: https://codereview.chromium.org/1682793002
---
 bench/Sk4fBench.cpp | 28 ++++++++--------------------
 1 file changed, 8 insertions(+), 20 deletions(-)

diff --git a/bench/Sk4fBench.cpp b/bench/Sk4fBench.cpp
index 823e14c0af..d5201fa2f0 100644
--- a/bench/Sk4fBench.cpp
+++ b/bench/Sk4fBench.cpp
@@ -9,16 +9,8 @@
 #include "SkColor.h"
 #include "SkNx.h"
 
-// Used to prevent the compiler from optimizing away the whole loop.
-volatile uint64_t blackhole = 0;
-
-// Not a great random number generator, but it's very fast.
-// The code we're measuring is quite fast, so low overhead is essential.
-static uint64_t lcg_rand(uint64_t* seed) {
-    *seed *= 1664525;
-    *seed += 1013904223;
-    return *seed;
-}
+// Writing into this array prevents the loops from being compiled away.
+static volatile float blackhole[4];
 
 template <typename T>
 struct Sk4fRoundtripBench : public Benchmark {
@@ -28,6 +20,7 @@ struct Sk4fRoundtripBench : public Benchmark {
         switch (sizeof(T)) {
             case 1: return "Sk4f_roundtrip_u8";
             case 2: return "Sk4f_roundtrip_u16";
+            case 4: return "Sk4f_roundtrip_int";
         }
         SkASSERT(false);
         return "";
@@ -36,21 +29,16 @@ struct Sk4fRoundtripBench : public Benchmark {
     bool isSuitableFor(Backend backend) override { return backend == kNonRendering_Backend; }
 
     void onDraw(int loops, SkCanvas* canvas) override {
-        // Unlike blackhole, junk can and probably will be a register.
-        uint64_t junk = 0;
-        uint64_t seed = 0;
-        for (int i = 0; i < loops; i++) {
-            uint64_t src = lcg_rand(&seed),
-                     back;
-            auto f = SkNx_cast<float>(SkNx<4,T>::Load(&src));
-            SkNx_cast<T>(f).store(&back);
-            junk ^= back;
+        Sk4f fs(1,2,3,4);
+        while (loops --> 0) {
+            fs = SkNx_cast<float>(SkNx_cast<T>(fs));
         }
-        blackhole ^= junk;
+        fs.store((float*)blackhole);
     }
 };
 DEF_BENCH(return new Sk4fRoundtripBench<uint8_t>;)
 DEF_BENCH(return new Sk4fRoundtripBench<uint16_t>;)
+DEF_BENCH(return new Sk4fRoundtripBench<int>;)
 
 struct Sk4fGradientBench : public Benchmark {
     const char* onGetName() override { return "Sk4f_gradient"; }