[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, 2 insertions, 80 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyUtilities.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyUtilities.cpp
index f1cb579..4edd546 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyUtilities.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyUtilities.cpp
@@ -242,50 +242,10 @@ bool WebAssembly::isMarker(const MachineInstr &MI) {
   }
 }
 
-bool WebAssembly::isThrow(const MachineInstr &MI) {
-  switch (MI.getOpcode()) {
-  case WebAssembly::THROW_I32:
-  case WebAssembly::THROW_I32_S:
-  case WebAssembly::THROW_I64:
-  case WebAssembly::THROW_I64_S:
-    return true;
-  default:
-    return false;
-  }
-}
-
-bool WebAssembly::isRethrow(const MachineInstr &MI) {
-  switch (MI.getOpcode()) {
-  case WebAssembly::RETHROW:
-  case WebAssembly::RETHROW_S:
-  case WebAssembly::RETHROW_TO_CALLER:
-  case WebAssembly::RETHROW_TO_CALLER_S:
-    return true;
-  default:
-    return false;
-  }
-}
-
-bool WebAssembly::isCatch(const MachineInstr &MI) {
-  switch (MI.getOpcode()) {
-  case WebAssembly::CATCH_I32:
-  case WebAssembly::CATCH_I32_S:
-  case WebAssembly::CATCH_I64:
-  case WebAssembly::CATCH_I64_S:
-  case WebAssembly::CATCH_ALL:
-  case WebAssembly::CATCH_ALL_S:
-    return true;
-  default:
-    return false;
-  }
-}
-
 bool WebAssembly::mayThrow(const MachineInstr &MI) {
   switch (MI.getOpcode()) {
-  case WebAssembly::THROW_I32:
-  case WebAssembly::THROW_I32_S:
-  case WebAssembly::THROW_I64:
-  case WebAssembly::THROW_I64_S:
+  case WebAssembly::THROW:
+  case WebAssembly::THROW_S:
   case WebAssembly::RETHROW:
   case WebAssembly::RETHROW_S:
     return true;
@@ -308,41 +268,3 @@ bool WebAssembly::mayThrow(const MachineInstr &MI) {
     return false;
   return true;
 }
-
-bool WebAssembly::isCatchTerminatePad(const MachineBasicBlock &MBB) {
-  if (!MBB.isEHPad())
-    return false;
-  bool SeenCatch = false;
-  for (auto &MI : MBB) {
-    if (MI.getOpcode() == WebAssembly::CATCH_I32 ||
-        MI.getOpcode() == WebAssembly::CATCH_I64 ||
-        MI.getOpcode() == WebAssembly::CATCH_I32_S ||
-        MI.getOpcode() == WebAssembly::CATCH_I64_S)
-      SeenCatch = true;
-    if (SeenCatch && MI.isCall()) {
-      const MachineOperand &CalleeOp = MI.getOperand(getCalleeOpNo(MI));
-      if (CalleeOp.isGlobal() &&
-          CalleeOp.getGlobal()->getName() == ClangCallTerminateFn)
-        return true;
-    }
-  }
-  return false;
-}
-
-bool WebAssembly::isCatchAllTerminatePad(const MachineBasicBlock &MBB) {
-  if (!MBB.isEHPad())
-    return false;
-  bool SeenCatchAll = false;
-  for (auto &MI : MBB) {
-    if (MI.getOpcode() == WebAssembly::CATCH_ALL ||
-        MI.getOpcode() == WebAssembly::CATCH_ALL_S)
-      SeenCatchAll = true;
-    if (SeenCatchAll && MI.isCall()) {
-      const MachineOperand &CalleeOp = MI.getOperand(getCalleeOpNo(MI));
-      if (CalleeOp.isGlobal() &&
-          CalleeOp.getGlobal()->getName() == StdTerminateFn)
-        return true;
-    }
-  }
-  return false;
-}