CodeGen support for x86_64 SEH catch handlers in LLVM

This adds handling for ExceptionHandling::MSVC, used by the
x86_64-pc-windows-msvc triple. It assumes that filter functions have
already been outlined in either the frontend or the backend. Filter
functions are used in place of the landingpad catch clause type info
operands. In catch clause order, the first filter to return true will
catch the exception.

The C specific handler table expects the landing pad to be split into
one block per handler, but LLVM IR uses a single landing pad for all
possible unwind actions. This patch papers over the mismatch by
synthesizing single instruction BBs for every catch clause to fill in
the EH selector that the landing pad block expects.

Missing functionality:
- Accessing data in the parent frame from outlined filters
- Cleanups (from __finally) are unsupported, as they will require
  outlining and parent frame access
- Filter clauses are unsupported, as there's no clear analogue in SEH

In other words, this is the minimal set of changes needed to write IR to
catch arbitrary exceptions and resume normal execution.

Reviewers: majnemer

Differential Revision: http://reviews.llvm.org/D6300

llvm-svn: 225904

3 files changed, 94 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 151bc724df6..86a63eea7c2 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2071,10 +2071,14 @@ void SelectionDAGBuilder::visitLandingPad(const LandingPadInst &LP) {
   // Get the two live-in registers as SDValues. The physregs have already been
   // copied into virtual registers.
   SDValue Ops[2];
-  Ops[0] = DAG.getZExtOrTrunc(
-      DAG.getCopyFromReg(DAG.getEntryNode(), getCurSDLoc(),
-                         FuncInfo.ExceptionPointerVirtReg, TLI.getPointerTy()),
-      getCurSDLoc(), ValueVTs[0]);
+  if (FuncInfo.ExceptionPointerVirtReg) {
+    Ops[0] = DAG.getZExtOrTrunc(
+        DAG.getCopyFromReg(DAG.getEntryNode(), getCurSDLoc(),
+                           FuncInfo.ExceptionPointerVirtReg, TLI.getPointerTy()),
+        getCurSDLoc(), ValueVTs[0]);
+  } else {
+    Ops[0] = DAG.getConstant(0, TLI.getPointerTy());
+  }
   Ops[1] = DAG.getZExtOrTrunc(
       DAG.getCopyFromReg(DAG.getEntryNode(), getCurSDLoc(),
                          FuncInfo.ExceptionSelectorVirtReg, TLI.getPointerTy()),
@@ -2086,6 +2090,27 @@ void SelectionDAGBuilder::visitLandingPad(const LandingPadInst &LP) {
   setValue(&LP, Res);
 }
 
+unsigned
+SelectionDAGBuilder::visitLandingPadClauseBB(GlobalValue *ClauseGV,
+                                             MachineBasicBlock *LPadBB) {
+  SDValue Chain = getControlRoot();
+
+  // Get the typeid that we will dispatch on later.
+  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+  const TargetRegisterClass *RC = TLI.getRegClassFor(TLI.getPointerTy());
+  unsigned VReg = FuncInfo.MF->getRegInfo().createVirtualRegister(RC);
+  unsigned TypeID = DAG.getMachineFunction().getMMI().getTypeIDFor(ClauseGV);
+  SDValue Sel = DAG.getConstant(TypeID, TLI.getPointerTy());
+  Chain = DAG.getCopyToReg(Chain, getCurSDLoc(), VReg, Sel);
+
+  // Branch to the main landing pad block.
+  MachineBasicBlock *ClauseMBB = FuncInfo.MBB;
+  ClauseMBB->addSuccessor(LPadBB);
+  DAG.setRoot(DAG.getNode(ISD::BR, getCurSDLoc(), MVT::Other, Chain,
+                          DAG.getBasicBlock(LPadBB)));
+  return VReg;
+}
+
 /// handleSmallSwitchCaseRange - Emit a series of specific tests (suitable for
 /// small case ranges).
 bool SelectionDAGBuilder::handleSmallSwitchRange(CaseRec& CR,
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
index 8216a0223cd..c1f483186d9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
@@ -713,6 +713,8 @@ public:
   void visitJumpTable(JumpTable &JT);
   void visitJumpTableHeader(JumpTable &JT, JumpTableHeader &JTH,
                             MachineBasicBlock *SwitchBB);
+  unsigned visitLandingPadClauseBB(GlobalValue *ClauseGV,
+                                   MachineBasicBlock *LPadMBB);
 
 private:
   // These all get lowered before this pass.
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 79109b7b8e6..a3f0fa47dd9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -19,6 +19,7 @@
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/CFG.h"
+#include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/FastISel.h"
 #include "llvm/CodeGen/FunctionLoweringInfo.h"
 #include "llvm/CodeGen/GCMetadata.h"
@@ -40,6 +41,7 @@
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
+#include "llvm/MC/MCAsmInfo.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -892,6 +894,8 @@ void SelectionDAGISel::DoInstructionSelection() {
 void SelectionDAGISel::PrepareEHLandingPad() {
   MachineBasicBlock *MBB = FuncInfo->MBB;
 
+  const TargetRegisterClass *PtrRC = TLI->getRegClassFor(TLI->getPointerTy());
+
   // Add a label to mark the beginning of the landing pad.  Deletion of the
   // landing pad can thus be detected via the MachineModuleInfo.
   MCSymbol *Label = MF->getMMI().addLandingPad(MBB);
@@ -903,8 +907,66 @@ void SelectionDAGISel::PrepareEHLandingPad() {
   BuildMI(*MBB, FuncInfo->InsertPt, SDB->getCurDebugLoc(), II)
     .addSym(Label);
 
+  if (TM.getMCAsmInfo()->getExceptionHandlingType() ==
+      ExceptionHandling::MSVC) {
+    // Make virtual registers and a series of labels that fill in values for the
+    // clauses.
+    auto &RI = MF->getRegInfo();
+    FuncInfo->ExceptionSelectorVirtReg = RI.createVirtualRegister(PtrRC);
+
+    // Get all invoke BBs that will unwind into the clause BBs.
+    SmallVector<MachineBasicBlock *, 4> InvokeBBs(MBB->pred_begin(),
+                                                  MBB->pred_end());
+
+    // Emit separate machine basic blocks with separate labels for each clause
+    // before the main landing pad block.
+    const BasicBlock *LLVMBB = MBB->getBasicBlock();
+    const LandingPadInst *LPadInst = LLVMBB->getLandingPadInst();
+    MachineInstrBuilder SelectorPHI = BuildMI(
+        *MBB, MBB->begin(), SDB->getCurDebugLoc(), TII->get(TargetOpcode::PHI),
+        FuncInfo->ExceptionSelectorVirtReg);
+    for (unsigned I = 0, E = LPadInst->getNumClauses(); I != E; ++I) {
+      MachineBasicBlock *ClauseBB = MF->CreateMachineBasicBlock(LLVMBB);
+      MF->insert(MBB, ClauseBB);
+
+      // Add the edge from the invoke to the clause.
+      for (MachineBasicBlock *InvokeBB : InvokeBBs)
+        InvokeBB->addSuccessor(ClauseBB);
+
+      // Mark the clause as a landing pad or MI passes will delete it.
+      ClauseBB->setIsLandingPad();
+
+      GlobalValue *ClauseGV = ExtractTypeInfo(LPadInst->getClause(I));
+
+      // Start the BB with a label.
+      MCSymbol *ClauseLabel = MF->getMMI().addClauseForLandingPad(MBB);
+      BuildMI(*ClauseBB, ClauseBB->begin(), SDB->getCurDebugLoc(), II)
+          .addSym(ClauseLabel);
+
+      // Construct a simple BB that defines a register with the typeid constant.
+      FuncInfo->MBB = ClauseBB;
+      FuncInfo->InsertPt = ClauseBB->end();
+      unsigned VReg = SDB->visitLandingPadClauseBB(ClauseGV, MBB);
+      CurDAG->setRoot(SDB->getRoot());
+      SDB->clear();
+      CodeGenAndEmitDAG();
+
+      // Add the typeid virtual register to the phi in the main landing pad.
+      SelectorPHI.addReg(VReg).addMBB(ClauseBB);
+    }
+
+    // Remove the edge from the invoke to the lpad.
+    for (MachineBasicBlock *InvokeBB : InvokeBBs)
+      InvokeBB->removeSuccessor(MBB);
+
+    // Restore FuncInfo back to its previous state and select the main landing
+    // pad block.
+    FuncInfo->MBB = MBB;
+    FuncInfo->InsertPt = MBB->end();
+    return;
+  }
+
   // Mark exception register as live in.
-  const TargetRegisterClass *PtrRC = TLI->getRegClassFor(TLI->getPointerTy());
   if (unsigned Reg = TLI->getExceptionPointerRegister())
     FuncInfo->ExceptionPointerVirtReg = MBB->addLiveIn(Reg, PtrRC);