[SEH] Add 32-bit lowering for SEH __try

This re-lands r236052 and adds support for __exception_code().

In 32-bit SEH, the exception code is not available in eax. It is only
available in the filter function, and now we arrange to load it and
store it into an escaped variable in the parent frame.

As a consequence, we have to disable the "catch i8* null" optimization
on 32-bit and always generate a filter function. We can re-enable the
optimization if we detect an __except block that doesn't use the
exception code, but this probably isn't worth optimizing.

Reviewers: majnemer

Differential Revision: http://reviews.llvm.org/D10852

llvm-svn: 241171

4 files changed, 299 insertions, 158 deletions

diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
index 4c8501724bd..55ee48fd81f 100644
--- a/clang/lib/CodeGen/CGException.cpp
+++ b/clang/lib/CodeGen/CGException.cpp
@@ -20,6 +20,7 @@
 #include "clang/AST/StmtCXX.h"
 #include "clang/AST/StmtObjC.h"
 #include "clang/AST/StmtVisitor.h"
+#include "clang/Basic/TargetBuiltins.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/IntrinsicInst.h"
@@ -1279,14 +1280,6 @@ llvm::BasicBlock *CodeGenFunction::getEHResumeBlock(bool isCleanup) {
 }
 
 void CodeGenFunction::EmitSEHTryStmt(const SEHTryStmt &S) {
-  // FIXME: Implement SEH on other architectures.
-  const llvm::Triple &T = CGM.getTarget().getTriple();
-  if (T.getArch() != llvm::Triple::x86_64 ||
-      !T.isKnownWindowsMSVCEnvironment()) {
-    ErrorUnsupported(&S, "__try statement");
-    return;
-  }
-
   EnterSEHTryStmt(S);
   {
     JumpDest TryExit = getJumpDestInCurrentScope("__try.__leave");
@@ -1311,25 +1304,39 @@ struct PerformSEHFinally : EHScopeStack::Cleanup {
 
   void Emit(CodeGenFunction &CGF, Flags F) override {
     ASTContext &Context = CGF.getContext();
-    QualType ArgTys[2] = {Context.UnsignedCharTy, Context.VoidPtrTy};
-    FunctionProtoType::ExtProtoInfo EPI;
-    const auto *FTP = cast<FunctionType>(
-        Context.getFunctionType(Context.VoidTy, ArgTys, EPI));
+    CodeGenModule &CGM = CGF.CGM;
 
+    // In 64-bit, we call the child function with arguments. In 32-bit, we store
+    // zero in the parent frame and use framerecover to check the value.
+    const CGFunctionInfo *FnInfo;
     CallArgList Args;
-    llvm::Value *IsForEH =
-        llvm::ConstantInt::get(CGF.ConvertType(ArgTys[0]), F.isForEHCleanup());
-    Args.add(RValue::get(IsForEH), ArgTys[0]);
+    if (CGF.getTarget().getTriple().getArch() != llvm::Triple::x86) {
+      // Compute the two argument values.
+      QualType ArgTys[2] = {Context.UnsignedCharTy, Context.VoidPtrTy};
+      llvm::Value *FrameAddr = CGM.getIntrinsic(llvm::Intrinsic::frameaddress);
+      llvm::Value *FP =
+          CGF.Builder.CreateCall(FrameAddr, {CGF.Builder.getInt32(0)});
+      llvm::Value *IsForEH =
+          llvm::ConstantInt::get(CGF.ConvertType(ArgTys[0]), F.isForEHCleanup());
+      Args.add(RValue::get(IsForEH), ArgTys[0]);
+      Args.add(RValue::get(FP), ArgTys[1]);
+
+      // Arrange a two-arg function info and type.
+      FunctionProtoType::ExtProtoInfo EPI;
+      const auto *FPT = cast<FunctionProtoType>(
+          Context.getFunctionType(Context.VoidTy, ArgTys, EPI));
+      FnInfo = &CGM.getTypes().arrangeFreeFunctionCall(Args, FPT,
+                                                       /*chainCall=*/false);
+    } else {
+      // Emit the zero store if this is normal control flow. There are no
+      // explicit arguments.
+      if (F.isForNormalCleanup() && CGF.ChildAbnormalTerminationSlot)
+        CGF.Builder.CreateStore(CGF.Builder.getInt32(0),
+                                CGF.ChildAbnormalTerminationSlot);
+      FnInfo = &CGM.getTypes().arrangeNullaryFunction();
+    }
 
-    CodeGenModule &CGM = CGF.CGM;
-    llvm::Value *Zero = llvm::ConstantInt::get(CGM.Int32Ty, 0);
-    llvm::Value *FrameAddr = CGM.getIntrinsic(llvm::Intrinsic::frameaddress);
-    llvm::Value *FP = CGF.Builder.CreateCall(FrameAddr, Zero);
-    Args.add(RValue::get(FP), ArgTys[1]);
-
-    const CGFunctionInfo &FnInfo =
-        CGM.getTypes().arrangeFreeFunctionCall(Args, FTP, /*chainCall=*/false);
-    CGF.EmitCall(FnInfo, OutlinedFinally, ReturnValueSlot(), Args);
+    CGF.EmitCall(*FnInfo, OutlinedFinally, ReturnValueSlot(), Args);
   }
 };
 }
@@ -1340,9 +1347,16 @@ struct CaptureFinder : ConstStmtVisitor<CaptureFinder> {
   CodeGenFunction &ParentCGF;
   const VarDecl *ParentThis;
   SmallVector<const VarDecl *, 4> Captures;
+  llvm::Value *AbnormalTermination = nullptr;
+  llvm::Value *SEHCodeSlot = nullptr;
   CaptureFinder(CodeGenFunction &ParentCGF, const VarDecl *ParentThis)
       : ParentCGF(ParentCGF), ParentThis(ParentThis) {}
 
+  // Return true if we need to do any capturing work.
+  bool foundCaptures() {
+    return !Captures.empty() || AbnormalTermination || SEHCodeSlot;
+  }
+
   void Visit(const Stmt *S) {
     // See if this is a capture, then recurse.
     ConstStmtVisitor<CaptureFinder>::Visit(S);
@@ -1366,25 +1380,116 @@ struct CaptureFinder : ConstStmtVisitor<CaptureFinder> {
   void VisitCXXThisExpr(const CXXThisExpr *E) {
     Captures.push_back(ParentThis);
   }
+
+  void VisitCallExpr(const CallExpr *E) {
+    // We only need to add parent frame allocations for these builtins in x86.
+    if (ParentCGF.getTarget().getTriple().getArch() != llvm::Triple::x86)
+      return;
+
+    unsigned ID = E->getBuiltinCallee();
+    switch (ID) {
+    case Builtin::BI__abnormal_termination:
+    case Builtin::BI_abnormal_termination:
+      // This is the simple case where we are the outermost finally. All we
+      // have to do here is make sure we escape this and recover it in the
+      // outlined handler.
+      if (!AbnormalTermination)
+        AbnormalTermination = ParentCGF.CreateMemTemp(
+            ParentCGF.getContext().IntTy, "abnormal_termination");
+      break;
+    case Builtin::BI__exception_code:
+    case Builtin::BI_exception_code:
+      // This is the simple case where we are the outermost finally. All we
+      // have to do here is make sure we escape this and recover it in the
+      // outlined handler.
+      if (!SEHCodeSlot)
+        SEHCodeSlot = ParentCGF.SEHCodeSlotStack.back();
+      break;
+    }
+  }
 };
 }
 
+llvm::Value *CodeGenFunction::recoverAddrOfEscapedLocal(
+    CodeGenFunction &ParentCGF, llvm::Value *ParentVar, llvm::Value *ParentFP) {
+  llvm::CallInst *RecoverCall = nullptr;
+  CGBuilderTy Builder(AllocaInsertPt);
+  if (auto *ParentAlloca = dyn_cast<llvm::AllocaInst>(ParentVar)) {
+    // Mark the variable escaped if nobody else referenced it and compute the
+    // frameescape index.
+    auto InsertPair = ParentCGF.EscapedLocals.insert(
+        std::make_pair(ParentAlloca, ParentCGF.EscapedLocals.size()));
+    int FrameEscapeIdx = InsertPair.first->second;
+    // call i8* @llvm.framerecover(i8* bitcast(@parentFn), i8* %fp, i32 N)
+    llvm::Function *FrameRecoverFn = llvm::Intrinsic::getDeclaration(
+        &CGM.getModule(), llvm::Intrinsic::framerecover);
+    llvm::Constant *ParentI8Fn =
+        llvm::ConstantExpr::getBitCast(ParentCGF.CurFn, Int8PtrTy);
+    RecoverCall = Builder.CreateCall(
+        FrameRecoverFn, {ParentI8Fn, ParentFP,
+                         llvm::ConstantInt::get(Int32Ty, FrameEscapeIdx)});
+
+  } else {
+    // If the parent didn't have an alloca, we're doing some nested outlining.
+    // Just clone the existing framerecover call, but tweak the FP argument to
+    // use our FP value. All other arguments are constants.
+    auto *ParentRecover =
+        cast<llvm::IntrinsicInst>(ParentVar->stripPointerCasts());
+    assert(ParentRecover->getIntrinsicID() == llvm::Intrinsic::framerecover &&
+           "expected alloca or framerecover in parent LocalDeclMap");
+    RecoverCall = cast<llvm::CallInst>(ParentRecover->clone());
+    RecoverCall->setArgOperand(1, ParentFP);
+    RecoverCall->insertBefore(AllocaInsertPt);
+  }
+
+  // Bitcast the variable, rename it, and insert it in the local decl map.
+  llvm::Value *ChildVar =
+      Builder.CreateBitCast(RecoverCall, ParentVar->getType());
+  ChildVar->setName(ParentVar->getName());
+  return ChildVar;
+}
+
 void CodeGenFunction::EmitCapturedLocals(CodeGenFunction &ParentCGF,
                                          const Stmt *OutlinedStmt,
-                                         llvm::Value *ParentFP) {
+                                         bool IsFilter) {
   // Find all captures in the Stmt.
   CaptureFinder Finder(ParentCGF, ParentCGF.CXXABIThisDecl);
   Finder.Visit(OutlinedStmt);
 
-  // Typically there are no captures and we can exit early.
-  if (Finder.Captures.empty())
+  // We can exit early on x86_64 when there are no captures. We just have to
+  // save the exception code in filters so that __exception_code() works.
+  if (!Finder.foundCaptures() &&
+      CGM.getTarget().getTriple().getArch() != llvm::Triple::x86) {
+    if (IsFilter)
+      EmitSEHExceptionCodeSave(ParentCGF, nullptr, nullptr);
     return;
+  }
 
-  // Prepare the first two arguments to llvm.framerecover.
-  llvm::Function *FrameRecoverFn = llvm::Intrinsic::getDeclaration(
-      &CGM.getModule(), llvm::Intrinsic::framerecover);
-  llvm::Constant *ParentI8Fn =
-      llvm::ConstantExpr::getBitCast(ParentCGF.CurFn, Int8PtrTy);
+  llvm::Value *EntryEBP = nullptr;
+  llvm::Value *ParentFP;
+  if (CGM.getTarget().getTriple().getArch() != llvm::Triple::x86) {
+    // On x64, the parent FP is passed as the second argument.
+    auto AI = CurFn->arg_begin();
+    ++AI;
+    ParentFP = AI;
+  } else {
+    // The end of the EH registration is passed in as the EBP physical register.
+    // We can recover that with llvm.frameaddress(1), and adjust that to
+    // recover the parent's true frame pointer.
+    CGBuilderTy Builder(AllocaInsertPt);
+    EntryEBP = Builder.CreateCall(
+        CGM.getIntrinsic(llvm::Intrinsic::frameaddress), {Builder.getInt32(1)});
+    llvm::Function *RecoverFPIntrin =
+        CGM.getIntrinsic(llvm::Intrinsic::x86_seh_recoverfp);
+    llvm::Constant *ParentI8Fn =
+        llvm::ConstantExpr::getBitCast(ParentCGF.CurFn, Int8PtrTy);
+    ParentFP = Builder.CreateCall(RecoverFPIntrin, {ParentI8Fn, EntryEBP});
+
+    // Inlining will break llvm.frameaddress(1), so disable it.
+    // FIXME: We could teach the inliner about the special meaning of
+    // frameaddress, framerecover, and frameescape to remove this limitation.
+    CurFn->addFnAttr(llvm::Attribute::NoInline);
+  }
 
   // Create llvm.framerecover calls for all captures.
   for (const VarDecl *VD : Finder.Captures) {
@@ -1407,49 +1512,70 @@ void CodeGenFunction::EmitCapturedLocals(CodeGenFunction &ParentCGF,
       continue;
     llvm::Value *ParentVar = I->second;
 
-    llvm::CallInst *RecoverCall = nullptr;
-    CGBuilderTy Builder(AllocaInsertPt);
-    if (auto *ParentAlloca = dyn_cast<llvm::AllocaInst>(ParentVar)) {
-      // Mark the variable escaped if nobody else referenced it and compute the
-      // frameescape index.
-      auto InsertPair =
-          ParentCGF.EscapedLocals.insert(std::make_pair(ParentAlloca, -1));
-      if (InsertPair.second)
-        InsertPair.first->second = ParentCGF.EscapedLocals.size() - 1;
-      int FrameEscapeIdx = InsertPair.first->second;
-      // call i8* @llvm.framerecover(i8* bitcast(@parentFn), i8* %fp, i32 N)
-      RecoverCall = Builder.CreateCall(
-          FrameRecoverFn, {ParentI8Fn, ParentFP,
-                           llvm::ConstantInt::get(Int32Ty, FrameEscapeIdx)});
+    LocalDeclMap[VD] =
+        recoverAddrOfEscapedLocal(ParentCGF, ParentVar, ParentFP);
+  }
 
-    } else {
-      // If the parent didn't have an alloca, we're doing some nested outlining.
-      // Just clone the existing framerecover call, but tweak the FP argument to
-      // use our FP value. All other arguments are constants.
-      auto *ParentRecover =
-          cast<llvm::IntrinsicInst>(ParentVar->stripPointerCasts());
-      assert(ParentRecover->getIntrinsicID() == llvm::Intrinsic::framerecover &&
-             "expected alloca or framerecover in parent LocalDeclMap");
-      RecoverCall = cast<llvm::CallInst>(ParentRecover->clone());
-      RecoverCall->setArgOperand(1, ParentFP);
-      RecoverCall->insertBefore(AllocaInsertPt);
-    }
+  // The __abnormal_termination and __exception_code values are just more
+  // captures.
+  if (Finder.AbnormalTermination) {
+    AbnormalTerminationSlot = recoverAddrOfEscapedLocal(
+        ParentCGF, Finder.AbnormalTermination, ParentFP);
+    // Save the slot on the parent so it can store 1 and 0 to it.
+    ParentCGF.ChildAbnormalTerminationSlot = Finder.AbnormalTermination;
+  }
 
-    // Bitcast the variable, rename it, and insert it in the local decl map.
-    llvm::Value *ChildVar =
-        Builder.CreateBitCast(RecoverCall, ParentVar->getType());
-    ChildVar->setName(ParentVar->getName());
-    LocalDeclMap[VD] = ChildVar;
+  if (Finder.SEHCodeSlot) {
+    SEHCodeSlotStack.push_back(
+        recoverAddrOfEscapedLocal(ParentCGF, Finder.SEHCodeSlot, ParentFP));
   }
+
+  if (IsFilter)
+    EmitSEHExceptionCodeSave(ParentCGF, ParentFP, EntryEBP);
 }
 
 /// Arrange a function prototype that can be called by Windows exception
 /// handling personalities. On Win64, the prototype looks like:
 /// RetTy func(void *EHPtrs, void *ParentFP);
 void CodeGenFunction::startOutlinedSEHHelper(CodeGenFunction &ParentCGF,
-                                             StringRef Name, QualType RetTy,
-                                             FunctionArgList &Args,
+                                             bool IsFilter,
                                              const Stmt *OutlinedStmt) {
+  SourceLocation StartLoc = OutlinedStmt->getLocStart();
+
+  // Get the mangled function name.
+  SmallString<128> Name;
+  {
+    llvm::raw_svector_ostream OS(Name);
+    const Decl *ParentCodeDecl = ParentCGF.CurCodeDecl;
+    const NamedDecl *Parent = dyn_cast_or_null<NamedDecl>(ParentCodeDecl);
+    assert(Parent && "FIXME: handle unnamed decls (lambdas, blocks) with SEH");
+    MangleContext &Mangler = CGM.getCXXABI().getMangleContext();
+    if (IsFilter)
+      Mangler.mangleSEHFilterExpression(Parent, OS);
+    else
+      Mangler.mangleSEHFinallyBlock(Parent, OS);
+  }
+
+  FunctionArgList Args;
+  if (CGM.getTarget().getTriple().getArch() != llvm::Triple::x86) {
+    if (IsFilter) {
+      Args.push_back(ImplicitParamDecl::Create(
+          getContext(), nullptr, StartLoc,
+          &getContext().Idents.get("exception_pointers"),
+          getContext().VoidPtrTy));
+    } else {
+      Args.push_back(ImplicitParamDecl::Create(
+          getContext(), nullptr, StartLoc,
+          &getContext().Idents.get("abnormal_termination"),
+          getContext().UnsignedCharTy));
+    }
+    Args.push_back(ImplicitParamDecl::Create(
+        getContext(), nullptr, StartLoc,
+        &getContext().Idents.get("frame_pointer"), getContext().VoidPtrTy));
+  }
+
+  QualType RetTy = IsFilter ? getContext().LongTy : getContext().VoidTy;
+
   llvm::Function *ParentFn = ParentCGF.CurFn;
   const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeFreeFunctionDeclaration(
       RetTy, Args, FunctionType::ExtInfo(), /*isVariadic=*/false);
@@ -1474,10 +1600,7 @@ void CodeGenFunction::startOutlinedSEHHelper(CodeGenFunction &ParentCGF,
                 OutlinedStmt->getLocStart(), OutlinedStmt->getLocStart());
 
   CGM.SetLLVMFunctionAttributes(nullptr, FnInfo, CurFn);
-
-  auto AI = Fn->arg_begin();
-  ++AI;
-  EmitCapturedLocals(ParentCGF, OutlinedStmt, &*AI);
+  EmitCapturedLocals(ParentCGF, OutlinedStmt, IsFilter);
 }
 
 /// Create a stub filter function that will ultimately hold the code of the
@@ -1487,37 +1610,7 @@ llvm::Function *
 CodeGenFunction::GenerateSEHFilterFunction(CodeGenFunction &ParentCGF,
                                            const SEHExceptStmt &Except) {
   const Expr *FilterExpr = Except.getFilterExpr();
-  SourceLocation StartLoc = FilterExpr->getLocStart();
-
-  SEHPointersDecl = ImplicitParamDecl::Create(
-      getContext(), nullptr, StartLoc,
-      &getContext().Idents.get("exception_pointers"), getContext().VoidPtrTy);
-  FunctionArgList Args;
-  Args.push_back(SEHPointersDecl);
-  Args.push_back(ImplicitParamDecl::Create(
-      getContext(), nullptr, StartLoc,
-      &getContext().Idents.get("frame_pointer"), getContext().VoidPtrTy));
-
-  // Get the mangled function name.
-  SmallString<128> Name;
-  {
-    llvm::raw_svector_ostream OS(Name);
-    const Decl *ParentCodeDecl = ParentCGF.CurCodeDecl;
-    const NamedDecl *Parent = dyn_cast_or_null<NamedDecl>(ParentCodeDecl);
-    assert(Parent && "FIXME: handle unnamed decls (lambdas, blocks) with SEH");
-    CGM.getCXXABI().getMangleContext().mangleSEHFilterExpression(Parent, OS);
-  }
-
-  startOutlinedSEHHelper(ParentCGF, Name, getContext().LongTy, Args,
-                         FilterExpr);
-
-  // Mark finally block calls as nounwind and noinline to make LLVM's job a
-  // little easier.
-  // FIXME: Remove these restrictions in the future.
-  CurFn->addFnAttr(llvm::Attribute::NoUnwind);
-  CurFn->addFnAttr(llvm::Attribute::NoInline);
-
-  EmitSEHExceptionCodeSave();
+  startOutlinedSEHHelper(ParentCGF, true, FilterExpr);
 
   // Emit the original filter expression, convert to i32, and return.
   llvm::Value *R = EmitScalarExpr(FilterExpr);
@@ -1534,29 +1627,13 @@ llvm::Function *
 CodeGenFunction::GenerateSEHFinallyFunction(CodeGenFunction &ParentCGF,
                                             const SEHFinallyStmt &Finally) {
   const Stmt *FinallyBlock = Finally.getBlock();
-  SourceLocation StartLoc = FinallyBlock->getLocStart();
-
-  FunctionArgList Args;
-  Args.push_back(ImplicitParamDecl::Create(
-      getContext(), nullptr, StartLoc,
-      &getContext().Idents.get("abnormal_termination"),
-      getContext().UnsignedCharTy));
-  Args.push_back(ImplicitParamDecl::Create(
-      getContext(), nullptr, StartLoc,
-      &getContext().Idents.get("frame_pointer"), getContext().VoidPtrTy));
+  startOutlinedSEHHelper(ParentCGF, false, FinallyBlock);
 
-  // Get the mangled function name.
-  SmallString<128> Name;
-  {
-    llvm::raw_svector_ostream OS(Name);
-    const Decl *ParentCodeDecl = ParentCGF.CurCodeDecl;
-    const NamedDecl *Parent = dyn_cast_or_null<NamedDecl>(ParentCodeDecl);
-    assert(Parent && "FIXME: handle unnamed decls (lambdas, blocks) with SEH");
-    CGM.getCXXABI().getMangleContext().mangleSEHFinallyBlock(Parent, OS);
-  }
-
-  startOutlinedSEHHelper(ParentCGF, Name, getContext().VoidTy, Args,
-                         FinallyBlock);
+  // Mark finally block calls as nounwind and noinline to make LLVM's job a
+  // little easier.
+  // FIXME: Remove these restrictions in the future.
+  CurFn->addFnAttr(llvm::Attribute::NoUnwind);
+  CurFn->addFnAttr(llvm::Attribute::NoInline);
 
   // Emit the original filter expression, convert to i32, and return.
   EmitStmt(FinallyBlock);
@@ -1566,47 +1643,63 @@ CodeGenFunction::GenerateSEHFinallyFunction(CodeGenFunction &ParentCGF,
   return CurFn;
 }
 
-void CodeGenFunction::EmitSEHExceptionCodeSave() {
+void CodeGenFunction::EmitSEHExceptionCodeSave(CodeGenFunction &ParentCGF,
+                                               llvm::Value *ParentFP,
+                                               llvm::Value *EntryEBP) {
+  // Get the pointer to the EXCEPTION_POINTERS struct. This is returned by the
+  // __exception_info intrinsic.
+  if (CGM.getTarget().getTriple().getArch() != llvm::Triple::x86) {
+    // On Win64, the info is passed as the first parameter to the filter.
+    auto AI = CurFn->arg_begin();
+    SEHInfo = AI;
+    SEHCodeSlotStack.push_back(
+        CreateMemTemp(getContext().IntTy, "__exception_code"));
+  } else {
+    // On Win32, the EBP on entry to the filter points to the end of an
+    // exception registration object. It contains 6 32-bit fields, and the info
+    // pointer is stored in the second field. So, GEP 20 bytes backwards and
+    // load the pointer.
+    SEHInfo = Builder.CreateConstInBoundsGEP1_32(Int8Ty, EntryEBP, -20);
+    SEHInfo = Builder.CreateBitCast(SEHInfo, Int8PtrTy->getPointerTo());
+    SEHInfo = Builder.CreateLoad(Int8PtrTy, SEHInfo);
+    SEHCodeSlotStack.push_back(recoverAddrOfEscapedLocal(
+        ParentCGF, ParentCGF.SEHCodeSlotStack.back(), ParentFP));
+  }
+
   // Save the exception code in the exception slot to unify exception access in
   // the filter function and the landing pad.
   // struct EXCEPTION_POINTERS {
   //   EXCEPTION_RECORD *ExceptionRecord;
   //   CONTEXT *ContextRecord;
   // };
-  // void *exn.slot =
-  //     (void *)(uintptr_t)exception_pointers->ExceptionRecord->ExceptionCode;
-  llvm::Value *Ptrs = Builder.CreateLoad(GetAddrOfLocalVar(SEHPointersDecl));
+  // int exceptioncode = exception_pointers->ExceptionRecord->ExceptionCode;
   llvm::Type *RecordTy = CGM.Int32Ty->getPointerTo();
   llvm::Type *PtrsTy = llvm::StructType::get(RecordTy, CGM.VoidPtrTy, nullptr);
-  Ptrs = Builder.CreateBitCast(Ptrs, PtrsTy->getPointerTo());
+  llvm::Value *Ptrs = Builder.CreateBitCast(SEHInfo, PtrsTy->getPointerTo());
   llvm::Value *Rec = Builder.CreateStructGEP(PtrsTy, Ptrs, 0);
   Rec = Builder.CreateLoad(Rec);
   llvm::Value *Code = Builder.CreateLoad(Rec);
-  Code = Builder.CreateZExt(Code, CGM.IntPtrTy);
-  // FIXME: Change landing pads to produce {i32, i32} and make the exception
-  // slot an i32.
-  Code = Builder.CreateIntToPtr(Code, CGM.VoidPtrTy);
-  Builder.CreateStore(Code, getExceptionSlot());
+  assert(!SEHCodeSlotStack.empty() && "emitting EH code outside of __except");
+  Builder.CreateStore(Code, SEHCodeSlotStack.back());
 }
 
 llvm::Value *CodeGenFunction::EmitSEHExceptionInfo() {
   // Sema should diagnose calling this builtin outside of a filter context, but
   // don't crash if we screw up.
-  if (!SEHPointersDecl)
+  if (!SEHInfo)
     return llvm::UndefValue::get(Int8PtrTy);
-  return Builder.CreateLoad(GetAddrOfLocalVar(SEHPointersDecl));
+  assert(SEHInfo->getType() == Int8PtrTy);
+  return SEHInfo;
 }
 
 llvm::Value *CodeGenFunction::EmitSEHExceptionCode() {
-  // If we're in a landing pad or filter function, the exception slot contains
-  // the code.
-  assert(ExceptionSlot);
-  llvm::Value *Code =
-      Builder.CreatePtrToInt(getExceptionFromSlot(), CGM.IntPtrTy);
-  return Builder.CreateTrunc(Code, CGM.Int32Ty);
+  assert(!SEHCodeSlotStack.empty() && "emitting EH code outside of __except");
+  return Builder.CreateLoad(Int32Ty, SEHCodeSlotStack.back());
 }
 
 llvm::Value *CodeGenFunction::EmitSEHAbnormalTermination() {
+  if (CGM.getTarget().getTriple().getArch() == llvm::Triple::x86)
+    return Builder.CreateLoad(AbnormalTerminationSlot);
   // Abnormal termination is just the first parameter to the outlined finally
   // helper.
   auto AI = CurFn->arg_begin();
@@ -1616,9 +1709,15 @@ llvm::Value *CodeGenFunction::EmitSEHAbnormalTermination() {
 void CodeGenFunction::EnterSEHTryStmt(const SEHTryStmt &S) {
   CodeGenFunction HelperCGF(CGM, /*suppressNewContext=*/true);
   if (const SEHFinallyStmt *Finally = S.getFinallyHandler()) {
-    // Push a cleanup for __finally blocks.
+    // Outline the finally block.
     llvm::Function *FinallyFunc =
         HelperCGF.GenerateSEHFinallyFunction(*this, *Finally);
+
+    // Store 1 to indicate abnormal termination if an exception is thrown.
+    if (ChildAbnormalTerminationSlot)
+      Builder.CreateStore(Builder.getInt32(1), ChildAbnormalTerminationSlot);
+
+    // Push a cleanup for __finally blocks.
     EHStack.pushCleanup<PerformSEHFinally>(NormalAndEHCleanup, FinallyFunc);
     return;
   }
@@ -1627,12 +1726,16 @@ void CodeGenFunction::EnterSEHTryStmt(const SEHTryStmt &S) {
   const SEHExceptStmt *Except = S.getExceptHandler();
   assert(Except);
   EHCatchScope *CatchScope = EHStack.pushCatch(1);
+  SEHCodeSlotStack.push_back(
+      CreateMemTemp(getContext().IntTy, "__exception_code"));
 
-  // If the filter is known to evaluate to 1, then we can use the clause "catch
-  // i8* null".
+  // If the filter is known to evaluate to 1, then we can use the clause
+  // "catch i8* null". We can't do this on x86 because the filter has to save
+  // the exception code.
   llvm::Constant *C =
       CGM.EmitConstantExpr(Except->getFilterExpr(), getContext().IntTy, this);
-  if (C && C->isOneValue()) {
+  if (CGM.getTarget().getTriple().getArch() != llvm::Triple::x86 && C &&
+      C->isOneValue()) {
     CatchScope->setCatchAllHandler(0, createBasicBlock("__except"));
     return;
   }
@@ -1650,6 +1753,7 @@ void CodeGenFunction::ExitSEHTryStmt(const SEHTryStmt &S) {
   // Just pop the cleanup if it's a __finally block.
   if (S.getFinallyHandler()) {
     PopCleanupBlock();
+    ChildAbnormalTerminationSlot = nullptr;
     return;
   }
 
@@ -1664,6 +1768,7 @@ void CodeGenFunction::ExitSEHTryStmt(const SEHTryStmt &S) {
   if (!CatchScope.hasEHBranches()) {
     CatchScope.clearHandlerBlocks();
     EHStack.popCatch();
+    SEHCodeSlotStack.pop_back();
     return;
   }
 
@@ -1683,9 +1788,20 @@ void CodeGenFunction::ExitSEHTryStmt(const SEHTryStmt &S) {
 
   EmitBlockAfterUses(ExceptBB);
 
+  // On Win64, the exception pointer is the exception code. Copy it to the slot.
+  if (CGM.getTarget().getTriple().getArch() != llvm::Triple::x86) {
+    llvm::Value *Code =
+        Builder.CreatePtrToInt(getExceptionFromSlot(), IntPtrTy);
+    Code = Builder.CreateTrunc(Code, Int32Ty);
+    Builder.CreateStore(Code, SEHCodeSlotStack.back());
+  }
+
   // Emit the __except body.
   EmitStmt(Except->getBlock());
 
+  // End the lifetime of the exception code.
+  SEHCodeSlotStack.pop_back();
+
   if (HaveInsertPoint())
     Builder.CreateBr(ContBB);
 
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index bece41e9ecb..b36b6565b86 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -45,12 +45,12 @@ CodeGenFunction::CodeGenFunction(CodeGenModule &cgm, bool suppressNewContext)
       LambdaThisCaptureField(nullptr), NormalCleanupDest(nullptr),
       NextCleanupDestIndex(1), FirstBlockInfo(nullptr), EHResumeBlock(nullptr),
       ExceptionSlot(nullptr), EHSelectorSlot(nullptr),
-      AbnormalTerminationSlot(nullptr), SEHPointersDecl(nullptr),
-      DebugInfo(CGM.getModuleDebugInfo()), DisableDebugInfo(false),
-      DidCallStackSave(false), IndirectBranch(nullptr), PGO(cgm),
-      SwitchInsn(nullptr), SwitchWeights(nullptr), CaseRangeBlock(nullptr),
-      UnreachableBlock(nullptr), NumReturnExprs(0), NumSimpleReturnExprs(0),
-      CXXABIThisDecl(nullptr), CXXABIThisValue(nullptr), CXXThisValue(nullptr),
+      DebugInfo(CGM.getModuleDebugInfo()),
+      DisableDebugInfo(false), DidCallStackSave(false), IndirectBranch(nullptr),
+      PGO(cgm), SwitchInsn(nullptr), SwitchWeights(nullptr),
+      CaseRangeBlock(nullptr), UnreachableBlock(nullptr), NumReturnExprs(0),
+      NumSimpleReturnExprs(0), CXXABIThisDecl(nullptr),
+      CXXABIThisValue(nullptr), CXXThisValue(nullptr),
       CXXDefaultInitExprThis(nullptr), CXXStructorImplicitParamDecl(nullptr),
       CXXStructorImplicitParamValue(nullptr), OutermostConditional(nullptr),
       CurLexicalScope(nullptr), TerminateLandingPad(nullptr),
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index e396d6adb6c..a587f001f4b 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -324,11 +324,21 @@ public:
   /// write the current selector value into this alloca.
   llvm::AllocaInst *EHSelectorSlot;
 
-  llvm::AllocaInst *AbnormalTerminationSlot;
+  /// Entering and leaving an SEH __try / __finally scope causes stores to this
+  /// slot.
+  llvm::Value *ChildAbnormalTerminationSlot = nullptr;
 
-  /// The implicit parameter to SEH filter functions of type
-  /// 'EXCEPTION_POINTERS*'.
-  ImplicitParamDecl *SEHPointersDecl;
+  /// The SEH __abnormal_termination() intrinsic lowers down to loads from this
+  /// slot from a parent function.
+  llvm::Value *AbnormalTerminationSlot = nullptr;
+
+  /// A stack of exception code slots. Entering an __except block pushes a slot
+  /// on the stack and leaving pops one. The __exception_code() intrinsic loads
+  /// a value from the top of the stack.
+  SmallVector<llvm::Value *, 1> SEHCodeSlotStack;
+
+  /// Value returned by __exception_info intrinsic.
+  llvm::Value *SEHInfo = nullptr;
 
   /// Emits a landing pad for the current EH stack.
   llvm::BasicBlock *EmitLandingPad();
@@ -2048,8 +2058,7 @@ public:
   void EnterSEHTryStmt(const SEHTryStmt &S);
   void ExitSEHTryStmt(const SEHTryStmt &S);
 
-  void startOutlinedSEHHelper(CodeGenFunction &ParentCGF, StringRef Name,
-                              QualType RetTy, FunctionArgList &Args,
+  void startOutlinedSEHHelper(CodeGenFunction &ParentCGF, bool IsFilter,
                               const Stmt *OutlinedStmt);
 
   llvm::Function *GenerateSEHFilterFunction(CodeGenFunction &ParentCGF,
@@ -2058,7 +2067,9 @@ public:
   llvm::Function *GenerateSEHFinallyFunction(CodeGenFunction &ParentCGF,
                                              const SEHFinallyStmt &Finally);
 
-  void EmitSEHExceptionCodeSave();
+  void EmitSEHExceptionCodeSave(CodeGenFunction &ParentCGF,
+                                llvm::Value *ParentFP,
+                                llvm::Value *EntryEBP);
   llvm::Value *EmitSEHExceptionCode();
   llvm::Value *EmitSEHExceptionInfo();
   llvm::Value *EmitSEHAbnormalTermination();
@@ -2067,7 +2078,16 @@ public:
   /// each capture, mark the capture as escaped and emit a call to
   /// llvm.framerecover. Insert the framerecover result into the LocalDeclMap.
   void EmitCapturedLocals(CodeGenFunction &ParentCGF, const Stmt *OutlinedStmt,
-                          llvm::Value *ParentFP);
+                          bool IsFilter);
+
+  /// Recovers the address of a local in a parent function. ParentVar is the
+  /// address of the variable used in the immediate parent function. It can
+  /// either be an alloca or a call to llvm.framerecover if there are nested
+  /// outlined functions. ParentFP is the frame pointer of the outermost parent
+  /// frame.
+  llvm::Value *recoverAddrOfEscapedLocal(CodeGenFunction &ParentCGF,
+                                         llvm::Value *ParentVar,
+                                         llvm::Value *ParentFP);
 
   void EmitCXXForRangeStmt(const CXXForRangeStmt &S,
                            ArrayRef<const Attr *> Attrs = None);
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 6fca974d5b3..c4f6fd8df1c 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -25,6 +25,7 @@
 #include "clang/AST/StmtObjC.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/AST/TypeOrdering.h"
+#include "clang/Basic/TargetInfo.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Sema/Initialization.h"
 #include "clang/Sema/Lookup.h"
@@ -3649,6 +3650,10 @@ StmtResult Sema::ActOnSEHTryBlock(bool IsCXXTry, SourceLocation TryLoc,
   else
     Diag(TryLoc, diag::err_seh_try_outside_functions);
 
+  // Reject __try on unsupported targets.
+  if (!Context.getTargetInfo().isSEHTrySupported())
+    Diag(TryLoc, diag::err_seh_try_unsupported);
+
   return SEHTryStmt::Create(Context, IsCXXTry, TryLoc, TryBlock, Handler);
 }