initial checkin of SkSL compiler

src/sksl/ir/SkSLIndexExpression.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_INDEX
+#define SKSL_INDEX
+
+#include "SkSLExpression.h"
+#include "SkSLUtil.h"
+
+namespace SkSL {
+
+/**
+ * Given a type, returns the type that will resulting from extracting an array value from it.

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

typo: s/resulting/result/

+ */
+static std::shared_ptr<Type> index_type(std::shared_ptr<Type> type) {
+    if (type->kind() == Type::kMatrix_Kind) {
+        if (type->componentType() == kFloat_Type) {
+            switch (type->columns()) {
+                case 2: return kVec2_Type;
+                case 3: return kVec3_Type;
+                case 4: return kVec4_Type;
+                default: ASSERT(false);
+            }
+        } else {
+            ASSERT(type->componentType() == kDouble_Type);
+            switch (type->columns()) {
+                case 2: return kDVec2_Type;
+                case 3: return kDVec3_Type;
+                case 4: return kDVec4_Type;
+                default: ASSERT(false);
+            }
+        }
+    }
+    return type->componentType();
+}
+
+/**
+ * An expression which extracts a value from an array or matrix, as in 'm[2]'.
+ */
+struct IndexExpression : public Expression {
+    IndexExpression(std::unique_ptr<Expression> base, std::unique_ptr<Expression> index)
+    : INHERITED(base->fPosition, kIndex_Kind, index_type(base->fType))
+    , fBase(std::move(base))
+    , fIndex(std::move(index)) {
+        ASSERT(fIndex->fType == kInt_Type);
+    }
+
+    virtual std::string description() const override {

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

nit: remove virtual

+        return fBase->description() + "[" + fIndex->description() + "]";
+    }
+
+    const std::unique_ptr<Expression> fBase;
+    const std::unique_ptr<Expression> fIndex;
+
+    typedef Expression INHERITED;
+};
+
+} // namespace
+
+#endif