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diff --git a/contrib/llvm/lib/Target/WebAssembly/WebAssemblyFixFunctionBitcasts.cpp b/contrib/llvm/lib/Target/WebAssembly/WebAssemblyFixFunctionBitcasts.cpp
new file mode 100644
index 000000000000..666337acccce
--- /dev/null
+++ b/contrib/llvm/lib/Target/WebAssembly/WebAssemblyFixFunctionBitcasts.cpp
@@ -0,0 +1,234 @@
+//===-- WebAssemblyFixFunctionBitcasts.cpp - Fix function bitcasts --------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief Fix bitcasted functions.
+///
+/// WebAssembly requires caller and callee signatures to match, however in LLVM,
+/// some amount of slop is vaguely permitted. Detect mismatch by looking for
+/// bitcasts of functions and rewrite them to use wrapper functions instead.
+///
+/// This doesn't catch all cases, such as when a function's address is taken in
+/// one place and casted in another, but it works for many common cases.
+///
+/// Note that LLVM already optimizes away function bitcasts in common cases by
+/// dropping arguments as needed, so this pass only ends up getting used in less
+/// common cases.
+///
+//===----------------------------------------------------------------------===//
+
+#include "WebAssembly.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "wasm-fix-function-bitcasts"
+
+static cl::opt<bool> TemporaryWorkarounds(
+  "wasm-temporary-workarounds",
+  cl::desc("Apply certain temporary workarounds"),
+  cl::init(true), cl::Hidden);
+
+namespace {
+class FixFunctionBitcasts final : public ModulePass {
+  StringRef getPassName() const override {
+    return "WebAssembly Fix Function Bitcasts";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    ModulePass::getAnalysisUsage(AU);
+  }
+
+  bool runOnModule(Module &M) override;
+
+public:
+  static char ID;
+  FixFunctionBitcasts() : ModulePass(ID) {}
+};
+} // End anonymous namespace
+
+char FixFunctionBitcasts::ID = 0;
+ModulePass *llvm::createWebAssemblyFixFunctionBitcasts() {
+  return new FixFunctionBitcasts();
+}
+
+// Recursively descend the def-use lists from V to find non-bitcast users of
+// bitcasts of V.
+static void FindUses(Value *V, Function &F,
+                     SmallVectorImpl<std::pair<Use *, Function *>> &Uses,
+                     SmallPtrSetImpl<Constant *> &ConstantBCs) {
+  for (Use &U : V->uses()) {
+    if (BitCastOperator *BC = dyn_cast<BitCastOperator>(U.getUser()))
+      FindUses(BC, F, Uses, ConstantBCs);
+    else if (U.get()->getType() != F.getType()) {
+      CallSite CS(U.getUser());
+      if (!CS)
+        // Skip uses that aren't immediately called
+        continue;
+      Value *Callee = CS.getCalledValue();
+      if (Callee != V)
+        // Skip calls where the function isn't the callee
+        continue;
+      if (isa<Constant>(U.get())) {
+        // Only add constant bitcasts to the list once; they get RAUW'd
+        auto c = ConstantBCs.insert(cast<Constant>(U.get()));
+        if (!c.second)
+          continue;
+      }
+      Uses.push_back(std::make_pair(&U, &F));
+    }
+  }
+}
+
+// Create a wrapper function with type Ty that calls F (which may have a
+// different type). Attempt to support common bitcasted function idioms:
+//  - Call with more arguments than needed: arguments are dropped
+//  - Call with fewer arguments than needed: arguments are filled in with undef
+//  - Return value is not needed: drop it
+//  - Return value needed but not present: supply an undef
+//
+// For now, return nullptr without creating a wrapper if the wrapper cannot
+// be generated due to incompatible types.
+static Function *CreateWrapper(Function *F, FunctionType *Ty) {
+  Module *M = F->getParent();
+
+  Function *Wrapper =
+      Function::Create(Ty, Function::PrivateLinkage, "bitcast", M);
+  BasicBlock *BB = BasicBlock::Create(M->getContext(), "body", Wrapper);
+
+  // Determine what arguments to pass.
+  SmallVector<Value *, 4> Args;
+  Function::arg_iterator AI = Wrapper->arg_begin();
+  Function::arg_iterator AE = Wrapper->arg_end();
+  FunctionType::param_iterator PI = F->getFunctionType()->param_begin();
+  FunctionType::param_iterator PE = F->getFunctionType()->param_end();
+  for (; AI != AE && PI != PE; ++AI, ++PI) {
+    if (AI->getType() != *PI) {
+      Wrapper->eraseFromParent();
+      return nullptr;
+    }
+    Args.push_back(&*AI);
+  }
+  for (; PI != PE; ++PI)
+    Args.push_back(UndefValue::get(*PI));
+  if (F->isVarArg())
+    for (; AI != AE; ++AI)
+      Args.push_back(&*AI);
+
+  CallInst *Call = CallInst::Create(F, Args, "", BB);
+
+  // Determine what value to return.
+  if (Ty->getReturnType()->isVoidTy())
+    ReturnInst::Create(M->getContext(), BB);
+  else if (F->getFunctionType()->getReturnType()->isVoidTy())
+    ReturnInst::Create(M->getContext(), UndefValue::get(Ty->getReturnType()),
+                       BB);
+  else if (F->getFunctionType()->getReturnType() == Ty->getReturnType())
+    ReturnInst::Create(M->getContext(), Call, BB);
+  else {
+    Wrapper->eraseFromParent();
+    return nullptr;
+  }
+
+  return Wrapper;
+}
+
+bool FixFunctionBitcasts::runOnModule(Module &M) {
+  Function *Main = nullptr;
+  CallInst *CallMain = nullptr;
+  SmallVector<std::pair<Use *, Function *>, 0> Uses;
+  SmallPtrSet<Constant *, 2> ConstantBCs;
+
+  // Collect all the places that need wrappers.
+  for (Function &F : M) {
+    FindUses(&F, F, Uses, ConstantBCs);
+
+    // If we have a "main" function, and its type isn't
+    // "int main(int argc, char *argv[])", create an artificial call with it
+    // bitcasted to that type so that we generate a wrapper for it, so that
+    // the C runtime can call it.
+    if (!TemporaryWorkarounds && !F.isDeclaration() && F.getName() == "main") {
+      Main = &F;
+      LLVMContext &C = M.getContext();
+      Type *MainArgTys[] = {
+        PointerType::get(Type::getInt8PtrTy(C), 0),
+        Type::getInt32Ty(C)
+      };
+      FunctionType *MainTy = FunctionType::get(Type::getInt32Ty(C), MainArgTys,
+                                               /*isVarArg=*/false);
+      if (F.getFunctionType() != MainTy) {
+        Value *Args[] = {
+          UndefValue::get(MainArgTys[0]),
+          UndefValue::get(MainArgTys[1])
+        };
+        Value *Casted = ConstantExpr::getBitCast(Main,
+                                                 PointerType::get(MainTy, 0));
+        CallMain = CallInst::Create(Casted, Args, "call_main");
+        Use *UseMain = &CallMain->getOperandUse(2);
+        Uses.push_back(std::make_pair(UseMain, &F));
+      }
+    }
+  }
+
+  DenseMap<std::pair<Function *, FunctionType *>, Function *> Wrappers;
+
+  for (auto &UseFunc : Uses) {
+    Use *U = UseFunc.first;
+    Function *F = UseFunc.second;
+    PointerType *PTy = cast<PointerType>(U->get()->getType());
+    FunctionType *Ty = dyn_cast<FunctionType>(PTy->getElementType());
+
+    // If the function is casted to something like i8* as a "generic pointer"
+    // to be later casted to something else, we can't generate a wrapper for it.
+    // Just ignore such casts for now.
+    if (!Ty)
+      continue;
+
+    // Bitcasted vararg functions occur in Emscripten's implementation of
+    // EM_ASM, so suppress wrappers for them for now.
+    if (TemporaryWorkarounds && (Ty->isVarArg() || F->isVarArg()))
+      continue;
+
+    auto Pair = Wrappers.insert(std::make_pair(std::make_pair(F, Ty), nullptr));
+    if (Pair.second)
+      Pair.first->second = CreateWrapper(F, Ty);
+
+    Function *Wrapper = Pair.first->second;
+    if (!Wrapper)
+      continue;
+
+    if (isa<Constant>(U->get()))
+      U->get()->replaceAllUsesWith(Wrapper);
+    else
+      U->set(Wrapper);
+  }
+
+  // If we created a wrapper for main, rename the wrapper so that it's the
+  // one that gets called from startup.
+  if (CallMain) {
+    Main->setName("__original_main");
+    Function *MainWrapper =
+        cast<Function>(CallMain->getCalledValue()->stripPointerCasts());
+    MainWrapper->setName("main");
+    MainWrapper->setLinkage(Main->getLinkage());
+    MainWrapper->setVisibility(Main->getVisibility());
+    Main->setLinkage(Function::PrivateLinkage);
+    Main->setVisibility(Function::DefaultVisibility);
+    delete CallMain;
+  }
+
+  return true;
+}