[WebAssembly] Fix ScopeTops info in CFGStackify for EH pads

Summary:
When creating `ScopeTops` info for `try` ~ `catch` ~ `end_try`, we
should create not only `end_try` -> `try` mapping but also `catch` ->
`try` mapping as well. If this is not created, `block` and `end_block`
markers later added may span across an existing `catch`, resulting in
the incorrect code like:
```
try
  block     --|  (X)
catch         |
  end_block --|
end_try
```

Reviewers: dschuff

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58605

llvm-svn: 354945

1 files changed, 16 insertions, 5 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
index 9001787..35ca7b9 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
@@ -594,11 +594,22 @@ void WebAssemblyCFGStackify::placeTryMarker(MachineBasicBlock &MBB) {
               TII.get(WebAssembly::END_TRY));
   registerTryScope(Begin, End, &MBB);
 
-  // Track the farthest-spanning scope that ends at this point.
-  int Number = Cont->getNumber();
-  if (!ScopeTops[Number] ||
-      ScopeTops[Number]->getNumber() > Header->getNumber())
-    ScopeTops[Number] = Header;
+  // Track the farthest-spanning scope that ends at this point. We create two
+  // mappings: (BB with 'end_try' -> BB with 'try') and (BB with 'catch' -> BB
+  // with 'try'). We need to create 'catch' -> 'try' mapping here too because
+  // markers should not span across 'catch'. For example, this should not
+  // happen:
+  //
+  // try
+  //   block     --|  (X)
+  // catch         |
+  //   end_block --|
+  // end_try
+  for (int Number : {Cont->getNumber(), MBB.getNumber()}) {
+    if (!ScopeTops[Number] ||
+        ScopeTops[Number]->getNumber() > Header->getNumber())
+      ScopeTops[Number] = Header;
+  }
 }
 
 void WebAssemblyCFGStackify::removeUnnecessaryInstrs(MachineFunction &MF) {