centralize SI, Ctx, and load_and_inc()

We've got independent definitions of SI, LazyCtx/Ctx, and load_and_inc()
in _stages.cpp and _lowp.cpp.  It's a good time to centralize them,
taking _stages.cpp's SI and load_and_inc(), and _lowp's Ctx.

SI and load_and_inc() are uninterestingly different.  But using _lowp's
Ctx will let us get its prettier typed stage definitions into
_stages.cpp, but that is not not done here.

This is a pure refactor with no generated code changes.

Change-Id: I53260b0fdc71a77bf9e3ed6f3df3a2a4cbd2392b
Reviewed-on: https://skia-review.googlesource.com/47181
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/jumper/SkJumper_misc.h b/src/jumper/SkJumper_misc.h
index 09758fba7d..8f7ebb56ac 100644
--- a/src/jumper/SkJumper_misc.h
+++ b/src/jumper/SkJumper_misc.h
@@ -63,19 +63,21 @@ SI void* load_and_inc(void**& program) {
 #endif
 }
 
-// LazyCtx doesn't do anything unless you call operator T*(), encapsulating the logic
-// from above that stages without a context pointer are represented by just 1 void*.
-struct LazyCtx {
+// Lazily resolved on first cast.  Does nothing if cast to Ctx::None.
+struct Ctx {
+    using None = decltype(nullptr);
+
     void*   ptr;
     void**& program;
 
-    explicit LazyCtx(void**& p) : ptr(nullptr), program(p) {}
+    explicit Ctx(void**& p) : ptr(nullptr), program(p) {}
 
     template <typename T>
     operator T*() {
         if (!ptr) { ptr = load_and_inc(program); }
         return (T*)ptr;
     }
+    operator None() { return nullptr; }
 };
 
 #endif//SkJumper_misc_DEFINED