Remove empty switch statements from translated shaders

src/compiler.gypi

@@ -107,6 +107,8 @@
             'compiler/translator/RegenerateStructNames.h',
             'compiler/translator/RemoveArrayLengthMethod.cpp',
             'compiler/translator/RemoveArrayLengthMethod.h',
+            'compiler/translator/RemoveEmptySwitchStatements.cpp',
+            'compiler/translator/RemoveEmptySwitchStatements.h',
             'compiler/translator/RemoveInvariantDeclaration.cpp',
             'compiler/translator/RemoveInvariantDeclaration.h',
             'compiler/translator/RemoveNoOpCasesFromEndOfSwitchStatements.cpp',

src/compiler/translator/Compiler.cpp

@@ -28,6 +28,7 @@
 #include "compiler/translator/PruneNoOps.h"
 #include "compiler/translator/RegenerateStructNames.h"
 #include "compiler/translator/RemoveArrayLengthMethod.h"
+#include "compiler/translator/RemoveEmptySwitchStatements.h"
 #include "compiler/translator/RemoveInvariantDeclaration.h"
 #include "compiler/translator/RemoveNoOpCasesFromEndOfSwitchStatements.h"
 #include "compiler/translator/RemovePow.h"
@@ -393,6 +394,9 @@ TIntermBlock *TCompiler::compileTreeImpl(const char *const shaderStrings[],
         if (success)
             RemoveNoOpCasesFromEndOfSwitchStatements(root, &symbolTable);
 
+        // Remove empty switch statements - this makes output simpler.
+        RemoveEmptySwitchStatements(root);
+
         // Create the function DAG and check there is no recursion
         if (success)
             success = initCallDag(root);

src/compiler/translator/RemoveEmptySwitchStatements.cpp

+//
+// Copyright (c) 2017 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.
+//
+// RemoveEmptySwitchStatements.cpp: Remove switch statements that have an empty statement list.
+
+#include "compiler/translator/RemoveEmptySwitchStatements.h"
+
+#include "compiler/translator/IntermTraverse.h"
+
+namespace sh
+{
+
+namespace
+{
+
+class RemoveEmptySwitchStatementsTraverser : public TIntermTraverser
+{
+  public:
+    RemoveEmptySwitchStatementsTraverser() : TIntermTraverser(true, false, false) {}
+
+    bool visitSwitch(Visit visit, TIntermSwitch *node);
+};
+
+bool RemoveEmptySwitchStatementsTraverser::visitSwitch(Visit visit, TIntermSwitch *node)
+{
+    if (node->getStatementList()->getSequence()->empty())
+    {
+        // Just output the init statement.
+        if (node->getInit()->hasSideEffects())
+        {
+            queueReplacement(node->getInit(), OriginalNode::IS_DROPPED);
+        }
+        else
+        {
+            TIntermSequence emptyReplacement;
+            ASSERT(getParentNode()->getAsBlock());
+            mMultiReplacements.push_back(NodeReplaceWithMultipleEntry(getParentNode()->getAsBlock(),
+                                                                      node, emptyReplacement));
+        }
+        return false;  // Nothing inside the child nodes to traverse.
+    }
+    return true;
+}
+
+}  // anonymous namespace
+
+void RemoveEmptySwitchStatements(TIntermBlock *root)
+{
+    RemoveEmptySwitchStatementsTraverser traverser;
+    root->traverse(&traverser);
+    traverser.updateTree();
+}
+
+}  // namespace sh

src/compiler/translator/RemoveEmptySwitchStatements.h

+//
+// Copyright (c) 2017 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.
+//
+// RemoveEmptySwitchStatements.h: Remove switch statements that have an empty statement list.
+
+#ifndef COMPILER_TRANSLATOR_REMOVEEMPTYSWITCHSTATEMENTS_H_
+#define COMPILER_TRANSLATOR_REMOVEEMPTYSWITCHSTATEMENTS_H_
+
+namespace sh
+{
+class TIntermBlock;
+
+void RemoveEmptySwitchStatements(TIntermBlock *root);
+}
+
+#endif  // COMPILER_TRANSLATOR_REMOVEEMPTYSWITCHSTATEMENTS_H_
\ No newline at end of file

src/tests/gl_tests/GLSLTest.cpp

@@ -3691,6 +3691,30 @@ TEST_P(GLSLTest_ES3, NestedSwitchWithVariableDeclarationInside)
     EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::green);
 }
 
+// Test that an empty switch/case statement is translated in a way that compiles and executes the
+// init-statement.
+TEST_P(GLSLTest_ES3, EmptySwitch)
+{
+    const std::string &fragmentShader =
+        R"(#version 300 es
+
+        precision highp float;
+
+        uniform int u_zero;
+        out vec4 my_FragColor;
+
+        void main()
+        {
+            int i = u_zero;
+            switch(++i) {}
+            my_FragColor = (i == 1) ? vec4(0, 1, 0, 1) : vec4(1, 0, 0, 1);
+        })";
+
+    ANGLE_GL_PROGRAM(program, mSimpleVSSource, fragmentShader);
+    drawQuad(program.get(), "inputAttribute", 0.5f);
+    EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::green);
+}
+
 // Use this to select which configurations (e.g. which renderer, which GLES major version) these tests should be run against.
 ANGLE_INSTANTIATE_TEST(GLSLTest,
                        ES2_D3D9(),