1 files changed, 84 insertions, 0 deletions
diff --git a/lib/Transforms/NaCl/RemoveAsmMemory.cpp b/lib/Transforms/NaCl/RemoveAsmMemory.cpp
new file mode 100644
index 0000000000..5295fe5ff8
--- /dev/null
+++ b/lib/Transforms/NaCl/RemoveAsmMemory.cpp
@@ -0,0 +1,84 @@
+//===- RemoveAsmMemory.cpp - Remove ``asm("":::"memory")`` ----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass removes all instances of ``asm("":::"memory")``.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/Twine.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/InlineAsm.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/InstVisitor.h"
+#include "llvm/Pass.h"
+#include <string>
+
+using namespace llvm;
+
+namespace {
+class RemoveAsmMemory : public FunctionPass {
+public:
+  static char ID; // Pass identification, replacement for typeid
+  RemoveAsmMemory() : FunctionPass(ID) {
+    initializeRemoveAsmMemoryPass(*PassRegistry::getPassRegistry());
+  }
+
+  virtual bool runOnFunction(Function &F);
+};
+
+class AsmDirectivesVisitor : public InstVisitor<AsmDirectivesVisitor> {
+public:
+  AsmDirectivesVisitor(Function &F)
+      : F(F), C(F.getParent()->getContext()), ModifiedFunction(false) {}
+  ~AsmDirectivesVisitor() {}
+  bool modifiedFunction() const { return ModifiedFunction; }
+
+  /// Only Call Instructions are ever inline assembly directives.
+  void visitCallInst(CallInst &CI);
+
+private:
+  Function &F;
+  LLVMContext &C;
+  bool ModifiedFunction;
+
+  AsmDirectivesVisitor() LLVM_DELETED_FUNCTION;
+  AsmDirectivesVisitor(const AsmDirectivesVisitor &) LLVM_DELETED_FUNCTION;
+  AsmDirectivesVisitor &operator=(
+      const AsmDirectivesVisitor &) LLVM_DELETED_FUNCTION;
+};
+}
+
+char RemoveAsmMemory::ID = 0;
+INITIALIZE_PASS(RemoveAsmMemory, "remove-asm-memory",
+                "remove all instances of ``asm(\"\":::\"memory\")``", false,
+                false)
+
+bool RemoveAsmMemory::runOnFunction(Function &F) {
+  AsmDirectivesVisitor AV(F);
+  AV.visit(F);
+  return AV.modifiedFunction();
+}
+
+void AsmDirectivesVisitor::visitCallInst(CallInst &CI) {
+  if (!CI.isInlineAsm() ||
+      !cast<InlineAsm>(CI.getCalledValue())->isAsmMemory())
+    return;
+
+  // In NaCl ``asm("":::"memory")`` always comes in pairs, straddling a
+  // sequentially consistent fence. Other passes rewrite this fence to
+  // an equivalent stable NaCl intrinsic, meaning that this assembly can
+  // be removed.
+  CI.eraseFromParent();
+  ModifiedFunction = true;
+}
+
+namespace llvm {
+FunctionPass *createRemoveAsmMemoryPass() { return new RemoveAsmMemory(); }
+}