[WinEH] Create an llvm.x86.seh.exceptioninfo intrinsic

This intrinsic is like framerecover plus a load. It recovers the EH
registration stack allocation from the parent frame and loads the
exception information field out of it, giving back a pointer to an
EXCEPTION_POINTERS struct. It's designed for clang to use in SEH filter
expressions instead of accessing the EXCEPTION_POINTERS parameter that
is available on x64.

This required a minor change to MC to allow defining a label variable to
another absolute framerecover label variable.

llvm-svn: 239567

2 files changed, 42 insertions, 47 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 8e663097d71..a4c7d1620fc 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -15506,23 +15506,6 @@ static SDValue LowerINTRINSIC_WO_CHAIN(SDValue Op, const X86Subtarget *Subtarget
         DAG.getTargetExternalSymbol(Name.data(), VT, X86II::MO_NOPREFIX);
     return DAG.getNode(X86ISD::Wrapper, dl, VT, Result);
   }
-
-  case Intrinsic::eh_exceptioninfo: {
-    // Compute the symbol for the LSDA. We know it'll get emitted later.
-    MachineFunction &MF = DAG.getMachineFunction();
-    SDValue Op1 = Op.getOperand(1);
-    auto *Fn = cast<Function>(cast<GlobalAddressSDNode>(Op1)->getGlobal());
-    MCSymbol *LSDASym = MF.getMMI().getContext().getOrCreateLSDASymbol(
-        GlobalValue::getRealLinkageName(Fn->getName()));
-    StringRef Name = LSDASym->getName();
-    assert(Name.data()[Name.size()] == '\0' && "not null terminated");
-
-    // Generate a simple absolute symbol reference. This intrinsic is only
-    // supported on 32-bit Windows, which isn't PIC.
-    SDValue Result =
-        DAG.getTargetExternalSymbol(Name.data(), VT, X86II::MO_NOPREFIX);
-    return DAG.getNode(X86ISD::Wrapper, dl, VT, Result);
-  }
   }
 }
 
@@ -15707,14 +15690,49 @@ static SDValue LowerREADCYCLECOUNTER(SDValue Op, const X86Subtarget *Subtarget,
   return DAG.getMergeValues(Results, DL);
 }
 
+static SDValue LowerEXCEPTIONINFO(SDValue Op, const X86Subtarget *Subtarget,
+                                  SelectionDAG &DAG) {
+  MachineFunction &MF = DAG.getMachineFunction();
+  SDLoc dl(Op);
+  SDValue FnOp = Op.getOperand(2);
+  SDValue FPOp = Op.getOperand(3);
+
+  // Compute the symbol for the parent EH registration. We know it'll get
+  // emitted later.
+  auto *Fn = cast<Function>(cast<GlobalAddressSDNode>(FnOp)->getGlobal());
+  MCSymbol *ParentFrameSym =
+      MF.getMMI().getContext().getOrCreateParentFrameOffsetSymbol(
+          GlobalValue::getRealLinkageName(Fn->getName()));
+  StringRef Name = ParentFrameSym->getName();
+  assert(Name.data()[Name.size()] == '\0' && "not null terminated");
+
+  // Create a TargetExternalSymbol for the label to avoid any target lowering
+  // that would make this PC relative.
+  MVT PtrVT = Op.getSimpleValueType();
+  SDValue OffsetSym = DAG.getTargetExternalSymbol(Name.data(), PtrVT);
+  SDValue OffsetVal =
+      DAG.getNode(ISD::FRAME_ALLOC_RECOVER, dl, PtrVT, OffsetSym);
+
+  // Add the offset to the FP.
+  SDValue Add = DAG.getNode(ISD::ADD, dl, PtrVT, FPOp, OffsetVal);
+
+  // Load the second field of the struct, which is 4 bytes in. See
+  // WinEHStatePass for more info.
+  Add = DAG.getNode(ISD::ADD, dl, PtrVT, Add, DAG.getConstant(4, dl, PtrVT));
+  return DAG.getLoad(PtrVT, dl, DAG.getEntryNode(), Add, MachinePointerInfo(),
+                     false, false, false, 0);
+}
 
 static SDValue LowerINTRINSIC_W_CHAIN(SDValue Op, const X86Subtarget *Subtarget,
                                       SelectionDAG &DAG) {
   unsigned IntNo = cast<ConstantSDNode>(Op.getOperand(1))->getZExtValue();
 
   const IntrinsicData* IntrData = getIntrinsicWithChain(IntNo);
-  if (!IntrData)
+  if (!IntrData) {
+    if (IntNo == Intrinsic::x86_seh_exceptioninfo)
+      return LowerEXCEPTIONINFO(Op, Subtarget, DAG);
     return SDValue();
+  }
 
   SDLoc dl(Op);
   switch(IntrData->Type) {
diff --git a/llvm/lib/Target/X86/X86WinEHState.cpp b/llvm/lib/Target/X86/X86WinEHState.cpp
index afad3f930da..e037f08790c 100644
--- a/llvm/lib/Target/X86/X86WinEHState.cpp
+++ b/llvm/lib/Target/X86/X86WinEHState.cpp
@@ -67,8 +67,6 @@ private:
   void addCXXStateStoresToFunclet(Value *ParentRegNode, WinEHFuncInfo &FuncInfo,
                                   Function &F, int BaseState);
   void insertStateNumberStore(Value *ParentRegNode, Instruction *IP, int State);
-  iplist<Instruction>::iterator
-  rewriteExceptionInfoIntrinsics(IntrinsicInst *Intrin);
 
   Value *emitEHLSDA(IRBuilder<> &Builder, Function *F);
 
@@ -487,6 +485,12 @@ void WinEHStatePass::addCXXStateStoresToFunclet(Value *ParentRegNode,
 void WinEHStatePass::addSEHStateStores(Function &F, MachineModuleInfo &MMI) {
   WinEHFuncInfo &FuncInfo = MMI.getWinEHFuncInfo(&F);
 
+  // Remember and return the index that we used. We save it in WinEHFuncInfo so
+  // that we can lower llvm.x86.seh.exceptioninfo later in filter functions
+  // without too much trouble.
+  int RegNodeEscapeIndex = escapeRegNode(F);
+  FuncInfo.EHRegNodeEscapeIndex = RegNodeEscapeIndex;
+
   // Iterate all the instructions and emit state number stores.
   int CurState = 0;
   SmallPtrSet<BasicBlock *, 4> ExceptBlocks;
@@ -495,7 +499,6 @@ void WinEHStatePass::addSEHStateStores(Function &F, MachineModuleInfo &MMI) {
       if (auto *CI = dyn_cast<CallInst>(I)) {
         auto *Intrin = dyn_cast<IntrinsicInst>(CI);
         if (Intrin) {
-          I = rewriteExceptionInfoIntrinsics(Intrin);
           // Calls that "don't throw" are considered to be able to throw asynch
           // exceptions, but intrinsics cannot.
           continue;
@@ -542,32 +545,6 @@ void WinEHStatePass::addSEHStateStores(Function &F, MachineModuleInfo &MMI) {
   }
 }
 
-/// Rewrite llvm.eh.exceptioncode and llvm.eh.exceptioninfo to memory loads in
-/// IR.
-iplist<Instruction>::iterator
-WinEHStatePass::rewriteExceptionInfoIntrinsics(IntrinsicInst *Intrin) {
-  Intrinsic::ID ID = Intrin->getIntrinsicID();
-  if (ID != Intrinsic::eh_exceptioncode && ID != Intrinsic::eh_exceptioninfo)
-    return Intrin;
-
-  // RegNode->ExceptionPointers
-  IRBuilder<> Builder(Intrin);
-  Value *Ptrs =
-      Builder.CreateLoad(Builder.CreateStructGEP(RegNodeTy, RegNode, 1));
-  Value *Res;
-  if (ID == Intrinsic::eh_exceptioncode) {
-    // Ptrs->ExceptionRecord->Code
-    Ptrs = Builder.CreateBitCast(
-        Ptrs, Builder.getInt32Ty()->getPointerTo()->getPointerTo());
-    Value *Rec = Builder.CreateLoad(Ptrs);
-    Res = Builder.CreateLoad(Rec);
-  } else {
-    Res = Ptrs;
-  }
-  Intrin->replaceAllUsesWith(Res);
-  return Intrin->eraseFromParent();
-}
-
 void WinEHStatePass::insertStateNumberStore(Value *ParentRegNode,
                                             Instruction *IP, int State) {
   IRBuilder<> Builder(IP);