[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, 0 insertions, 14 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyExceptionInfo.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyExceptionInfo.cpp
index 4a316e5..0387957 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyExceptionInfo.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyExceptionInfo.cpp
@@ -50,10 +50,6 @@ void WebAssemblyExceptionInfo::recalculate(
     MachineBasicBlock *EHPad = DomNode->getBlock();
     if (!EHPad->isEHPad())
       continue;
-    // We group catch & catch-all terminate pads together, so skip the second
-    // one
-    if (WebAssembly::isCatchAllTerminatePad(*EHPad))
-      continue;
     auto *WE = new WebAssemblyException(EHPad);
     discoverAndMapException(WE, MDT, MDF);
     Exceptions.push_back(WE);
@@ -104,16 +100,6 @@ void WebAssemblyExceptionInfo::discoverAndMapException(
 
   // Map blocks that belong to a catchpad / cleanuppad
   MachineBasicBlock *EHPad = WE->getEHPad();
-
-  // We group catch & catch-all terminate pads together within an exception
-  if (WebAssembly::isCatchTerminatePad(*EHPad)) {
-    assert(EHPad->succ_size() == 1 &&
-           "Catch terminate pad has more than one successors");
-    changeExceptionFor(EHPad, WE);
-    changeExceptionFor(*(EHPad->succ_begin()), WE);
-    return;
-  }
-
   SmallVector<MachineBasicBlock *, 8> WL;
   WL.push_back(EHPad);
   while (!WL.empty()) {