[WebAssembly] Fix bugs in rethrow depth counting and InstPrinter

Summary:
EH stack depth is incremented at `try` and decremented at `catch`. When
there are more than two catch instructions for a try instruction, we
shouldn't count non-first catches when calculating EH stack depths.

This patch fixes two bugs:
- CFGStackify: Exclude `catch_all` in the terminate catch pad when
  calculating EH pad stack, because when we have multiple catches for a
  try we should count only the first catch instruction when calculating
  EH pad stack.
- InstPrinter: The initial intention was also to exclude non-first
  catches, but it didn't account nested try-catches, so it failed on
  this case:
```
try
  try
  catch
  end
catch    <-- (1)
end
```
In the example, when we are at the catch (1), the last seen EH
instruction is not `try` but `end_try`, violating the wrong assumption.

We don't need these after we switch to the second proposal because there
is gonna be only one `catch` instruction. But anyway before then these
bugfixes are necessary for keep trunk in working state.

Reviewers: dschuff

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

Differential Revision: https://reviews.llvm.org/D53819

llvm-svn: 346029

llvm/lib/Target/WebAssembly/InstPrinter/WebAssemblyInstPrinter.cpp

@@ -120,10 +120,9 @@ void WebAssemblyInstPrinter::printInst(const MCInst *MI, raw_ostream &OS,
     case WebAssembly::CATCH_I64_S:
     case WebAssembly::CATCH_ALL:
     case WebAssembly::CATCH_ALL_S:
-      assert(LastSeenEHInst != END_TRY);
       // There can be multiple catch instructions for one try instruction, so we
-      // only print 'catch' label when the last seen EH instruction was 'try'.
-      if (LastSeenEHInst == TRY) {
+      // print a label only for the first 'catch' label.
+      if (LastSeenEHInst != CATCH) {
         assert(!EHPadStack.empty() && "try-catch mismatch!");
         printAnnotation(OS, "catch" + utostr(EHPadStack.pop_back_val()) + ':');
       }

llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp

@@ -739,7 +739,20 @@ void WebAssemblyCFGStackify::rewriteDepthImmediates(MachineFunction &MF) {
       case WebAssembly::CATCH_I32:
       case WebAssembly::CATCH_I64:
       case WebAssembly::CATCH_ALL:
-        EHPadStack.push_back(&MBB);
+        // Currently the only case there are more than one catch for a try is
+        // for catch terminate pad, in the form of
+        //   try
+        //   catch
+        //     call @__clang_call_terminate
+        //     unreachable
+        //   catch_all
+        //     call @std::terminate
+        //     unreachable
+        //   end
+        // So we shouldn't push the current BB for the second catch_all block
+        // here.
+        if (!WebAssembly::isCatchAllTerminatePad(MBB))
+          EHPadStack.push_back(&MBB);
         break;
 
       case WebAssembly::LOOP:

llvm/test/CodeGen/WebAssembly/exception.ll

@@ -1,5 +1,6 @@
 ; RUN: not llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers -exception-model=wasm
 ; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers -exception-model=wasm -mattr=+exception-handling | FileCheck -allow-deprecated-dag-overlap %s
+; RUN: llc < %s -disable-wasm-fallthrough-return-opt -wasm-keep-registers -exception-model=wasm -mattr=+exception-handling
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"