1 files changed, 90 insertions, 0 deletions
diff --git a/gfx/skia/skia/src/sksl/transform/SkSLEliminateDeadGlobalVariables.cpp b/gfx/skia/skia/src/sksl/transform/SkSLEliminateDeadGlobalVariables.cpp
new file mode 100644
index 0000000000..700e176ca5
--- /dev/null
+++ b/gfx/skia/skia/src/sksl/transform/SkSLEliminateDeadGlobalVariables.cpp
@@ -0,0 +1,90 @@
+/*
+ * Copyright 2021 Google LLC
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "include/private/SkSLProgramElement.h"
+#include "src/base/SkStringView.h"
+#include "src/sksl/SkSLCompiler.h"
+#include "src/sksl/SkSLContext.h"
+#include "src/sksl/SkSLProgramSettings.h"
+#include "src/sksl/analysis/SkSLProgramUsage.h"
+#include "src/sksl/ir/SkSLProgram.h"
+#include "src/sksl/ir/SkSLVarDeclarations.h"
+#include "src/sksl/ir/SkSLVariable.h"
+#include "src/sksl/transform/SkSLTransform.h"
+
+#include <algorithm>
+#include <cstddef>
+#include <memory>
+#include <vector>
+
+namespace SkSL {
+
+static bool is_dead_variable(const ProgramElement& element,
+                             ProgramUsage* usage,
+                             bool onlyPrivateGlobals) {
+    if (!element.is<GlobalVarDeclaration>()) {
+        return false;
+    }
+    const GlobalVarDeclaration& global = element.as<GlobalVarDeclaration>();
+    const VarDeclaration& varDecl = global.varDeclaration();
+    if (onlyPrivateGlobals && !skstd::starts_with(varDecl.var()->name(), '$')) {
+        return false;
+    }
+    if (!usage->isDead(*varDecl.var())) {
+        return false;
+    }
+    // This declaration is about to be eliminated by remove_if; update ProgramUsage accordingly.
+    usage->remove(&varDecl);
+    return true;
+}
+
+bool Transform::EliminateDeadGlobalVariables(const Context& context,
+                                             Module& module,
+                                             ProgramUsage* usage,
+                                             bool onlyPrivateGlobals) {
+    auto isDeadVariable = [&](const ProgramElement& element) {
+        return is_dead_variable(element, usage, onlyPrivateGlobals);
+    };
+
+    size_t numElements = module.fElements.size();
+    if (context.fConfig->fSettings.fRemoveDeadVariables) {
+        module.fElements.erase(std::remove_if(module.fElements.begin(),
+                                              module.fElements.end(),
+                                              [&](const std::unique_ptr<ProgramElement>& pe) {
+                                                  return isDeadVariable(*pe);
+                                              }),
+                               module.fElements.end());
+    }
+    return module.fElements.size() < numElements;
+}
+
+bool Transform::EliminateDeadGlobalVariables(Program& program) {
+    auto isDeadVariable = [&](const ProgramElement& element) {
+        return is_dead_variable(element, program.fUsage.get(), /*onlyPrivateGlobals=*/false);
+    };
+
+    size_t numOwnedElements = program.fOwnedElements.size();
+    size_t numSharedElements = program.fSharedElements.size();
+    if (program.fConfig->fSettings.fRemoveDeadVariables) {
+        program.fOwnedElements.erase(std::remove_if(program.fOwnedElements.begin(),
+                                                    program.fOwnedElements.end(),
+                                                    [&](const std::unique_ptr<ProgramElement>& pe) {
+                                                        return isDeadVariable(*pe);
+                                                    }),
+                                     program.fOwnedElements.end());
+        program.fSharedElements.erase(std::remove_if(program.fSharedElements.begin(),
+                                                     program.fSharedElements.end(),
+                                                     [&](const ProgramElement* pe) {
+                                                         return isDeadVariable(*pe);
+                                                     }),
+                                      program.fSharedElements.end());
+    }
+    return program.fOwnedElements.size() < numOwnedElements ||
+           program.fSharedElements.size() < numSharedElements;
+}
+
+}  // namespace SkSL