[WebAssembly] LSDA info generation

Summary:
This adds support for LSDA (exception table) generation for wasm EH.
Wasm EH mostly follows the structure of Itanium-style exception tables,
with one exception: a call site table entry in wasm EH corresponds to
not a call site but a landing pad.

In wasm EH, the VM is responsible for stack unwinding. After an
exception occurs and the stack is unwound, the control flow is
transferred to wasm 'catch' instruction by the VM, after which the
personality function is called from the compiler-generated code. (Refer
to WasmEHPrepare pass for more information on this part.)

This patch:
- Changes wasm.landingpad.index intrinsic to take a token argument, to
make this 1:1 match with a catchpad instruction
- Stores landingpad index info and catch type info MachineFunction in
before instruction selection
- Lowers wasm.lsda intrinsic to an MCSymbol pointing to the start of an
exception table
- Adds WasmException class with overridden methods for table generation
- Adds support for LSDA section in Wasm object writer

Reviewers: dschuff, sbc100, rnk

Subscribers: mgorny, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D52748

llvm-svn: 344575

1 files changed, 59 insertions, 24 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 2b4a590f19f..90bcaa653c3 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -27,6 +27,7 @@
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/EHPersonalities.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
@@ -1128,6 +1129,36 @@ static bool hasExceptionPointerOrCodeUser(const CatchPadInst *CPI) {
   return false;
 }
 
+// wasm.landingpad.index intrinsic is for associating a landing pad index number
+// with a catchpad instruction. Retrieve the landing pad index in the intrinsic
+// and store the mapping in the function.
+static void mapWasmLandingPadIndex(MachineBasicBlock *MBB,
+                                   const CatchPadInst *CPI) {
+  MachineFunction *MF = MBB->getParent();
+  // In case of single catch (...), we don't emit LSDA, so we don't need
+  // this information.
+  bool IsSingleCatchAllClause =
+      CPI->getNumArgOperands() == 1 &&
+      cast<Constant>(CPI->getArgOperand(0))->isNullValue();
+  if (!IsSingleCatchAllClause) {
+    // Create a mapping from landing pad label to landing pad index.
+    bool IntrFound = false;
+    for (const User *U : CPI->users()) {
+      if (const auto *Call = dyn_cast<IntrinsicInst>(U)) {
+        Intrinsic::ID IID = Call->getIntrinsicID();
+        if (IID == Intrinsic::wasm_landingpad_index) {
+          Value *IndexArg = Call->getArgOperand(1);
+          int Index = cast<ConstantInt>(IndexArg)->getZExtValue();
+          MF->setWasmLandingPadIndex(MBB, Index);
+          IntrFound = true;
+          break;
+        }
+      }
+    }
+    assert(IntrFound && "wasm.landingpad.index intrinsic not found!");
+  }
+}
+
 /// PrepareEHLandingPad - Emit an EH_LABEL, set up live-in registers, and
 /// do other setup for EH landing-pad blocks.
 bool SelectionDAGISel::PrepareEHLandingPad() {
@@ -1137,44 +1168,48 @@ bool SelectionDAGISel::PrepareEHLandingPad() {
   const TargetRegisterClass *PtrRC =
       TLI->getRegClassFor(TLI->getPointerTy(CurDAG->getDataLayout()));
 
+  auto Pers = classifyEHPersonality(PersonalityFn);
+
   // Catchpads have one live-in register, which typically holds the exception
   // pointer or code.
-  if (const auto *CPI = dyn_cast<CatchPadInst>(LLVMBB->getFirstNonPHI())) {
-    if (hasExceptionPointerOrCodeUser(CPI)) {
-      // Get or create the virtual register to hold the pointer or code.  Mark
-      // the live in physreg and copy into the vreg.
-      MCPhysReg EHPhysReg = TLI->getExceptionPointerRegister(PersonalityFn);
-      assert(EHPhysReg && "target lacks exception pointer register");
-      MBB->addLiveIn(EHPhysReg);
-      unsigned VReg = FuncInfo->getCatchPadExceptionPointerVReg(CPI, PtrRC);
-      BuildMI(*MBB, FuncInfo->InsertPt, SDB->getCurDebugLoc(),
-              TII->get(TargetOpcode::COPY), VReg)
-          .addReg(EHPhysReg, RegState::Kill);
+  if (isFuncletEHPersonality(Pers)) {
+    if (const auto *CPI = dyn_cast<CatchPadInst>(LLVMBB->getFirstNonPHI())) {
+      if (hasExceptionPointerOrCodeUser(CPI)) {
+        // Get or create the virtual register to hold the pointer or code.  Mark
+        // the live in physreg and copy into the vreg.
+        MCPhysReg EHPhysReg = TLI->getExceptionPointerRegister(PersonalityFn);
+        assert(EHPhysReg && "target lacks exception pointer register");
+        MBB->addLiveIn(EHPhysReg);
+        unsigned VReg = FuncInfo->getCatchPadExceptionPointerVReg(CPI, PtrRC);
+        BuildMI(*MBB, FuncInfo->InsertPt, SDB->getCurDebugLoc(),
+                TII->get(TargetOpcode::COPY), VReg)
+            .addReg(EHPhysReg, RegState::Kill);
+      }
     }
     return true;
   }
 
-  if (!LLVMBB->isLandingPad())
-    return true;
-
   // 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->addLandingPad(MBB);
 
-  // Assign the call site to the landing pad's begin label.
-  MF->setCallSiteLandingPad(Label, SDB->LPadToCallSiteMap[MBB]);
-
   const MCInstrDesc &II = TII->get(TargetOpcode::EH_LABEL);
   BuildMI(*MBB, FuncInfo->InsertPt, SDB->getCurDebugLoc(), II)
     .addSym(Label);
 
-  // Mark exception register as live in.
-  if (unsigned Reg = TLI->getExceptionPointerRegister(PersonalityFn))
-    FuncInfo->ExceptionPointerVirtReg = MBB->addLiveIn(Reg, PtrRC);
-
-  // Mark exception selector register as live in.
-  if (unsigned Reg = TLI->getExceptionSelectorRegister(PersonalityFn))
-    FuncInfo->ExceptionSelectorVirtReg = MBB->addLiveIn(Reg, PtrRC);
+  if (Pers == EHPersonality::Wasm_CXX) {
+    if (const auto *CPI = dyn_cast<CatchPadInst>(LLVMBB->getFirstNonPHI()))
+      mapWasmLandingPadIndex(MBB, CPI);
+  } else {
+    // Assign the call site to the landing pad's begin label.
+    MF->setCallSiteLandingPad(Label, SDB->LPadToCallSiteMap[MBB]);
+    // Mark exception register as live in.
+    if (unsigned Reg = TLI->getExceptionPointerRegister(PersonalityFn))
+      FuncInfo->ExceptionPointerVirtReg = MBB->addLiveIn(Reg, PtrRC);
+    // Mark exception selector register as live in.
+    if (unsigned Reg = TLI->getExceptionSelectorRegister(PersonalityFn))
+      FuncInfo->ExceptionSelectorVirtReg = MBB->addLiveIn(Reg, PtrRC);
+  }
 
   return true;
 }