Inline common cases of PackParam<BufferBinding>

This appears to improve frame time by ~0.8% in some of my
driver_overhead_2 tests on a mobile device.
Default implementation is FromGLenum<BufferBinding>
https://crsrc.org/c/third_party/angle/src/common/PackedGLEnums_autogen.cpp;drc=0bb109aa3311f35bf0b51bcda3d7e095048168c8;l=106
and has 15 cases. This CL avoids the call for 3 of those cases,
most common ones according to frequency of glBindBuffer arg
in our trace cpp files.

This mapping adds compare/branch instructions for each case, hence
inlining increases the caller a little. In this case the increase is
about 60 bytes. With the total of 23 callers (GL_*Buffer* exports), this
increase the .so size by ~1.3KB. Just inlining the function would yield
higher bloat and wouldn't prioritize the common cases.

Bug: b/383305597
Change-Id: Icc205fd46fb8ef195c8ffaf67f9cd5194d1d1a5d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6148838
Reviewed-by: Shahbaz Youssefi <[email protected]>
Reviewed-by: Geoff Lang <[email protected]>
Commit-Queue: Roman Lavrov <[email protected]>

src/common/PackedEnums.h

@@ -925,6 +925,27 @@ PackParam(FromT from)
         "Data types are different");
     return reinterpret_cast<EnumT>(from);
 }
+
+// Optimized specialization to avoid function call in common cases
+template <>
+ANGLE_INLINE typename gl::BufferBinding PackParam<gl::BufferBinding>(GLenum from)
+{
+    if (ANGLE_LIKELY(from == GL_ARRAY_BUFFER))
+    {
+        return gl::BufferBinding::Array;
+    }
+    if (ANGLE_LIKELY(from == GL_ELEMENT_ARRAY_BUFFER))
+    {
+        return gl::BufferBinding::ElementArray;
+    }
+    if (ANGLE_LIKELY(from == GL_UNIFORM_BUFFER))
+    {
+        return gl::BufferBinding::Uniform;
+    }
+
+    // Fall back to the default implementation
+    return FromGLenum<gl::BufferBinding>(from);
+}
 }  // namespace gl
 
 #endif  // COMMON_PACKEDGLENUMS_H_