initial checkin of SkSL compiler

src/sksl/ir/SkSLSwizzle.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+ 
+#ifndef SKSL_SWIZZLE
+#define SKSL_SWIZZLE
+
+#include "SkSLExpression.h"
+#include "SkSLUtil.h"
+
+namespace SkSL {
+
+/**
+ * Given a type and a swizzle component count, returns the type that will result from swizzling. For 
+ * instance, swizzling a vec3 with two components will result in a vec2. It is possible to swizzle
+ * with more components than the source vector, as in 'vec2(1).xxxx'.
+ */
+static std::shared_ptr<Type> get_type(Expression& value, 

[dogben, 2016/06/22 17:43:57]

nit: I'm used to all references being const, but I don't know what style Skia
normally uses.

[ethannicholas, 2016/06/24 21:23:10]

Normally I would have used const, but all of these types are immutable in the
first place -- does it matter?

[dogben, 2016/06/26 03:57:53]

Nope. :-)

The style I'm used to is that everything that can be const, is const; and all
reference parameters are const -- mutable parameters must be pointers. The
benefit is that (in most cases) the call site has an indication of whether the
callee can mutate the parameters. E.g.:
string x;
foo(&x); // foo could mutate x. (In most cases, this means foo *should* mutate
x.)
bar(x);  // bar can't mutate x.

To follow up on a previous comment, using "mutable" breaks the contract in this
style. It's still used for caches, where the externally-visible constness of the
object is preserved.

Again, this is just the style I'm used to. I wanted to give a little bit of
background for where some of my comments are coming from.

+                                      size_t count) {
+    std::shared_ptr<Type> base = value.fType->componentType();
+    if (count == 1) {
+        return base;
+    }
+    if (base == kFloat_Type) {
+        switch (count) {
+            case 1: return kFloat_Type;

[dogben, 2016/06/22 17:43:57]

nit: Aren't all the "case 1"s in this function redundant?

[ethannicholas, 2016/06/24 21:23:10]

What do you mean?

[dogben, 2016/06/26 03:57:53]

Sorry for being unclear. The "count == 1" case is handled above.

[ethannicholas, 2016/06/27 20:35:03]

Derp. Yes, it is.

+            case 2: return kVec2_Type;
+            case 3: return kVec3_Type;
+            case 4: return kVec4_Type;
+        }
+    } else if (base == kDouble_Type) {
+        switch (count) {
+            case 1: return kDouble_Type;
+            case 2: return kDVec2_Type;
+            case 3: return kDVec3_Type;
+            case 4: return kDVec4_Type;
+        }
+    } else if (base == kInt_Type) {
+        switch (count) {
+            case 1: return kInt_Type;
+            case 2: return kIVec2_Type;
+            case 3: return kIVec3_Type;
+            case 4: return kIVec4_Type;
+        }
+    } else if (base == kUInt_Type) {
+        switch (count) {
+            case 1: return kUInt_Type;
+            case 2: return kUVec2_Type;
+            case 3: return kUVec3_Type;
+            case 4: return kUVec4_Type;
+        }
+    } else if (base == kBool_Type) {
+        switch (count) {
+            case 1: return kBool_Type;
+            case 2: return kBVec2_Type;
+            case 3: return kBVec3_Type;
+            case 4: return kBVec4_Type;
+        }
+    }
+    ABORT("cannot swizzle %s\n", value.description().c_str());
+}
+
+/**
+ * Represents a vector swizzle operation such as 'vec2(1, 2, 3).zyx'.
+ */
+struct Swizzle : public Expression {
+    Swizzle(std::unique_ptr<Expression> base, std::vector<int> components)
+    : INHERITED(base->fPosition, kSwizzle_Kind, get_type(*base, components.size()))
+    , fBase(std::move(base))
+    , fComponents(components) {

[dogben, 2016/06/22 17:43:58]

nit: std::move

+        ASSERT(components.size() >= 1 && components.size() <= 4);
+    }
+
+    virtual std::string description() const override {

[dogben, 2016/06/22 17:43:58]

nit: remove virtual

+        std::string result = fBase->description() + ".";
+        for (int x : fComponents) {
+            result += "xyzw"[x];
+        }
+        return result;
+    }
+
+    const std::unique_ptr<Expression> fBase;
+    const std::vector<int> fComponents;
+
+    typedef Expression INHERITED;
+};
+
+} // namespace
+
+#endif