[WebAssembly] Exception handling: Switch to the new proposal

Summary:
This switches the EH implementation to the new proposal:
https://github.com/WebAssembly/exception-handling/blob/master/proposals/Exceptions.md
(The previous proposal was
 https://github.com/WebAssembly/exception-handling/blob/master/proposals/old/Exceptions.md)

- Instruction changes
  - Now we have one single `catch` instruction that returns a except_ref
    value
  - `throw` now can take variable number of operations
  - `rethrow` does not have 'depth' argument anymore
  - `br_on_exn` queries an except_ref to see if it matches the tag and
    branches to the given label if true.
  - `extract_exception` is a pseudo instruction that simulates popping
    values from wasm stack. This is to make `br_on_exn`, a very special
    instruction, work: `br_on_exn` puts values onto the stack only if it
    is taken, and the # of values can vay depending on the tag.

- Now there's only one `catch` per `try`, this patch removes all special
  handling for terminate pad with a call to `__clang_call_terminate`.
  Before it was the only case there are two catch clauses (a normal
  `catch` and `catch_all` per `try`).

- Make `rethrow` act as a terminator like `throw`. This splits BB after
  `rethrow` in WasmEHPrepare, and deletes an unnecessary `unreachable`
  after `rethrow` in LateEHPrepare.

- Now we stop at all catchpads (because we add wasm `catch` instruction
  that catches all exceptions), this creates new
  `findWasmUnwindDestinations` function in SelectionDAGBuilder.

- Now we use `br_on_exn` instrution to figure out if an except_ref
  matches the current tag or not, LateEHPrepare generates this sequence
  for catch pads:
```
  catch
  block i32
  br_on_exn $__cpp_exception
  end_block
  extract_exception
```

- Branch analysis for `br_on_exn` in WebAssemblyInstrInfo

- Other various misc. changes to switch to the new proposal.

Reviewers: dschuff

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D57134

llvm-svn: 352598

1 files changed, 35 insertions, 41 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
index 7cb7f2750ff..52d9d282159 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -884,13 +884,13 @@ SDValue WebAssemblyTargetLowering::LowerOperation(SDValue Op,
     return LowerFRAMEADDR(Op, DAG);
   case ISD::CopyToReg:
     return LowerCopyToReg(Op, DAG);
-  case ISD::INTRINSIC_WO_CHAIN:
-    return LowerINTRINSIC_WO_CHAIN(Op, DAG);
   case ISD::EXTRACT_VECTOR_ELT:
   case ISD::INSERT_VECTOR_ELT:
     return LowerAccessVectorElement(Op, DAG);
   case ISD::INTRINSIC_VOID:
-    return LowerINTRINSIC_VOID(Op, DAG);
+  case ISD::INTRINSIC_WO_CHAIN:
+  case ISD::INTRINSIC_W_CHAIN:
+    return LowerIntrinsic(Op, DAG);
   case ISD::SIGN_EXTEND_INREG:
     return LowerSIGN_EXTEND_INREG(Op, DAG);
   case ISD::BUILD_VECTOR:
@@ -1035,17 +1035,28 @@ SDValue WebAssemblyTargetLowering::LowerVASTART(SDValue Op,
                       MachinePointerInfo(SV), 0);
 }
 
-SDValue
-WebAssemblyTargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
-                                                   SelectionDAG &DAG) const {
-  unsigned IntNo = cast<ConstantSDNode>(Op.getOperand(0))->getZExtValue();
+SDValue WebAssemblyTargetLowering::LowerIntrinsic(SDValue Op,
+                                                  SelectionDAG &DAG) const {
+  MachineFunction &MF = DAG.getMachineFunction();
+  unsigned IntNo;
+  switch (Op.getOpcode()) {
+  case ISD::INTRINSIC_VOID:
+  case ISD::INTRINSIC_W_CHAIN:
+    IntNo = cast<ConstantSDNode>(Op.getOperand(1))->getZExtValue();
+    break;
+  case ISD::INTRINSIC_WO_CHAIN:
+    IntNo = cast<ConstantSDNode>(Op.getOperand(0))->getZExtValue();
+    break;
+  default:
+    llvm_unreachable("Invalid intrinsic");
+  }
   SDLoc DL(Op);
+
   switch (IntNo) {
   default:
     return {}; // Don't custom lower most intrinsics.
 
   case Intrinsic::wasm_lsda: {
-    MachineFunction &MF = DAG.getMachineFunction();
     EVT VT = Op.getValueType();
     const TargetLowering &TLI = DAG.getTargetLoweringInfo();
     MVT PtrVT = TLI.getPointerTy(DAG.getDataLayout());
@@ -1055,43 +1066,26 @@ WebAssemblyTargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
     return DAG.getNode(WebAssemblyISD::Wrapper, DL, VT,
                        DAG.getMCSymbol(S, PtrVT));
   }
-  }
-}
-
-SDValue
-WebAssemblyTargetLowering::LowerINTRINSIC_VOID(SDValue Op,
-                                               SelectionDAG &DAG) const {
-  MachineFunction &MF = DAG.getMachineFunction();
-  unsigned IntNo = cast<ConstantSDNode>(Op.getOperand(1))->getZExtValue();
-  SDLoc DL(Op);
-
-  switch (IntNo) {
-  default:
-    return {}; // Don't custom lower most intrinsics.
 
   case Intrinsic::wasm_throw: {
+    // We only support C++ exceptions for now
     int Tag = cast<ConstantSDNode>(Op.getOperand(2).getNode())->getZExtValue();
-    switch (Tag) {
-    case CPP_EXCEPTION: {
-      const TargetLowering &TLI = DAG.getTargetLoweringInfo();
-      MVT PtrVT = TLI.getPointerTy(DAG.getDataLayout());
-      const char *SymName = MF.createExternalSymbolName("__cpp_exception");
-      SDValue SymNode =
-          DAG.getNode(WebAssemblyISD::Wrapper, DL, PtrVT,
-                      DAG.getTargetExternalSymbol(
-                          SymName, PtrVT, WebAssemblyII::MO_SYMBOL_EVENT));
-      return DAG.getNode(WebAssemblyISD::THROW, DL,
-                         MVT::Other, // outchain type
-                         {
-                             Op.getOperand(0), // inchain
-                             SymNode,          // exception symbol
-                             Op.getOperand(3)  // thrown value
-                         });
-    }
-    default:
+    if (Tag != CPP_EXCEPTION)
       llvm_unreachable("Invalid tag!");
-    }
-    break;
+    const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+    MVT PtrVT = TLI.getPointerTy(DAG.getDataLayout());
+    const char *SymName = MF.createExternalSymbolName("__cpp_exception");
+    SDValue SymNode =
+        DAG.getNode(WebAssemblyISD::Wrapper, DL, PtrVT,
+                    DAG.getTargetExternalSymbol(
+                        SymName, PtrVT, WebAssemblyII::MO_SYMBOL_EVENT));
+    return DAG.getNode(WebAssemblyISD::THROW, DL,
+                       MVT::Other, // outchain type
+                       {
+                           Op.getOperand(0), // inchain
+                           SymNode,          // exception symbol
+                           Op.getOperand(3)  // thrown value
+                       });
   }
   }
 }