[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, 2 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/WasmException.cpp b/llvm/lib/CodeGen/AsmPrinter/WasmException.cpp
index 3f863ae4d69..444b0ed17b6 100644
--- a/llvm/lib/CodeGen/AsmPrinter/WasmException.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/WasmException.cpp
@@ -18,10 +18,10 @@
 using namespace llvm;
 
 void WasmException::endModule() {
-  // This is the symbol used in 'throw' and 'if_except' instruction to denote
+  // This is the symbol used in 'throw' and 'br_on_exn' instruction to denote
   // this is a C++ exception. This symbol has to be emitted somewhere once in
   // the module.  Check if the symbol has already been created, i.e., we have at
-  // least one 'throw' or 'if_except' instruction in the module, and emit the
+  // least one 'throw' or 'br_on_exn' instruction in the module, and emit the
   // symbol only if so.
   SmallString<60> NameStr;
   Mangler::getNameWithPrefix(NameStr, "__cpp_exception", Asm->getDataLayout());