HLSL: implement numthreads for compute shaders

This PR adds handling of the numthreads attribute for compute shaders, as well as a general
infrastructure for returning attribute values from acceptAttributes, which may be needed in other
cases, e.g, unroll(x), or merely to know if some attribute without params was given.

A map of enum values from TAttributeType to TIntermAggregate nodes is built and returned.  It
can be queried with operator[] on the map.  In the future there may be a need to also handle
strings (e.g, for patchconstantfunc), and those can be easily added into the class if needed.

New test is in hlsl.numthreads.comp.

hlsl/hlslAttributes.h

@@ -0,0 +1,96 @@
+//
+//Copyright (C) 2016 LunarG, Inc.
+//
+//All rights reserved.
+//
+//Redistribution and use in source and binary forms, with or without
+//modification, are permitted provided that the following conditions
+//are met:
+//
+//    Redistributions of source code must retain the above copyright
+//    notice, this list of conditions and the following disclaimer.
+//
+//    Redistributions in binary form must reproduce the above
+//    copyright notice, this list of conditions and the following
+//    disclaimer in the documentation and/or other materials provided
+//    with the distribution.
+//
+//    Neither the name of Google, Inc., nor the names of its
+//    contributors may be used to endorse or promote products derived
+//    from this software without specific prior written permission.
+//
+//THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+//"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+//LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+//FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+//COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+//INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+//BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+//LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+//CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+//LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+//ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+//POSSIBILITY OF SUCH DAMAGE.
+//
+
+#ifndef HLSLATTRIBUTES_H_
+#define HLSLATTRIBUTES_H_
+
+#include <unordered_map>
+#include <functional>
+#include "hlslScanContext.h"
+#include "../glslang/Include/Common.h"
+
+namespace glslang {
+    enum TAttributeType {
+        EatNone,
+        EatAllow_uav_condition,
+        EatBranch,
+        EatCall,
+        EatDomain,
+        EatEarlydepthstencil,
+        EatFastopt,
+        EatFlatten,
+        EatForcecase,
+        EatInstance,
+        EatMaxtessfactor,
+        EatNumthreads,
+        EatOutputcontrolpoints,
+        EatOutputtopology,
+        EatPartitioning,
+        EatPatchconstantfunc,
+        EatUnroll,
+    };
+}
+
+namespace std {
+    // Allow use of TAttributeType enum in hash_map without calling code having to cast.
+    template <> struct hash<glslang::TAttributeType> {
+        std::size_t operator()(glslang::TAttributeType attr) const {
+            return std::hash<int>()(int(attr));
+        }
+    };
+} // end namespace std
+
+namespace glslang {
+    class TIntermAggregate;
+
+    class TAttributeMap {
+    public:
+        // Search for and potentially add the attribute into the map.  Return the
+        // attribute type enum for it, if found, else EatNone.
+        TAttributeType setAttribute(const TString* name, TIntermAggregate* value);
+
+        // Const lookup: search for (but do not modify) the attribute in the map.
+        const TIntermAggregate* operator[](TAttributeType) const;
+
+    protected:
+        // Find an attribute enum given its name.
+        static TAttributeType attributeFromName(const TString&);
+
+        std::unordered_map<TAttributeType, TIntermAggregate*> attributes;
+    };
+} // end namespace glslang
+
+
+#endif // HLSLATTRIBUTES_H_