Prune empty declarations from the AST

src/compiler.gypi

@@ -78,6 +78,8 @@
             'compiler/translator/PoolAlloc.cpp',
             'compiler/translator/PoolAlloc.h',
             'compiler/translator/Pragma.h',
+            'compiler/translator/PruneEmptyDeclarations.cpp',
+            'compiler/translator/PruneEmptyDeclarations.h',
             'compiler/translator/QualifierAlive.cpp',
             'compiler/translator/QualifierAlive.h',
             'compiler/translator/RegenerateStructNames.cpp',

src/compiler/translator/Compiler.cpp

@@ -11,6 +11,7 @@
 #include "compiler/translator/InitializeParseContext.h"
 #include "compiler/translator/InitializeVariables.h"
 #include "compiler/translator/ParseContext.h"
+#include "compiler/translator/PruneEmptyDeclarations.h"
 #include "compiler/translator/RegenerateStructNames.h"
 #include "compiler/translator/RenameFunction.h"
 #include "compiler/translator/ScalarizeVecAndMatConstructorArgs.h"
@@ -249,6 +250,10 @@ TIntermNode *TCompiler::compileTreeImpl(const char* const shaderStrings[],
         if (success && !(compileOptions & SH_DONT_PRUNE_UNUSED_FUNCTIONS))
             success = pruneUnusedFunctions(root);
 
+        // Prune empty declarations to work around driver bugs and to keep declaration output simple.
+        if (success)
+            PruneEmptyDeclarations(root);
+
         if (success && shaderVersion == 300 && shaderType == GL_FRAGMENT_SHADER)
             success = validateOutputs(root);
 

src/compiler/translator/PruneEmptyDeclarations.cpp

+//
+// Copyright (c) 2002-2015 The ANGLE Project Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// The PruneEmptyDeclarations function prunes unnecessary empty declarations and declarators from the AST.
+
+#include "compiler/translator/PruneEmptyDeclarations.h"
+
+#include "compiler/translator/IntermNode.h"
+
+namespace
+{
+
+class PruneEmptyDeclarationsTraverser : private TIntermTraverser
+{
+  public:
+    static void apply(TIntermNode *root);
+  private:
+    PruneEmptyDeclarationsTraverser();
+    bool visitAggregate(Visit, TIntermAggregate *node) override;
+};
+
+void PruneEmptyDeclarationsTraverser::apply(TIntermNode *root)
+{
+    PruneEmptyDeclarationsTraverser prune;
+    root->traverse(&prune);
+    prune.updateTree();
+}
+
+PruneEmptyDeclarationsTraverser::PruneEmptyDeclarationsTraverser()
+    : TIntermTraverser(true, false, false)
+{
+}
+
+bool PruneEmptyDeclarationsTraverser::visitAggregate(Visit, TIntermAggregate *node)
+{
+    if (node->getOp() == EOpDeclaration)
+    {
+        TIntermSequence *sequence = node->getSequence();
+        if (sequence->size() >= 1)
+        {
+            TIntermSymbol *sym = sequence->front()->getAsSymbolNode();
+            // Prune declarations without a variable name, unless it's an interface block declaration.
+            if (sym != nullptr && sym->getSymbol() == "" && !sym->isInterfaceBlock())
+            {
+                if (sequence->size() > 1)
+                {
+                    // Generate a replacement that will remove the empty declarator in the beginning of a declarator
+                    // list. Example of a declaration that will be changed:
+                    // float, a;
+                    // will be changed to
+                    // float a;
+                    // This applies also to struct declarations.
+                    TIntermSequence emptyReplacement;
+                    mMultiReplacements.push_back(NodeReplaceWithMultipleEntry(node, sym, emptyReplacement));
+                }
+                else if (sym->getBasicType() != EbtStruct)
+                {
+                    // Single struct declarations may just declare the struct type and no variables, so they should
+                    // not be pruned. All other single empty declarations can be pruned entirely. Example of an empty
+                    // declaration that will be pruned:
+                    // float;
+                    TIntermSequence emptyReplacement;
+                    TIntermAggregate *parentAgg = getParentNode()->getAsAggregate();
+                    ASSERT(parentAgg != nullptr);
+                    mMultiReplacements.push_back(NodeReplaceWithMultipleEntry(parentAgg, node, emptyReplacement));
+                }
+            }
+        }
+        return false;
+    }
+    return true;
+}
+
+} // namespace
+
+void PruneEmptyDeclarations(TIntermNode *root)
+{
+    PruneEmptyDeclarationsTraverser::apply(root);
+}

src/compiler/translator/PruneEmptyDeclarations.h

+//
+// Copyright (c) 2002-2015 The ANGLE Project Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// The PruneEmptyDeclarations function prunes unnecessary empty declarations and declarators from the AST.
+
+#ifndef COMPILER_TRANSLATOR_PRUNEEMPTYDECLARATIONS_H_
+#define COMPILER_TRANSLATOR_PRUNEEMPTYDECLARATIONS_H_
+
+class TIntermNode;
+
+void PruneEmptyDeclarations(TIntermNode *root);
+
+#endif  // COMPILER_TRANSLATOR_PRUNEEMPTYDECLARATIONS_H_