[WebAssembly] Fix a bug when mixing TRY/LOOP markers

[aheejin]

Summary

When TRY and LOOP markers are in the same BB and END_TRY and END_LOOP
markers are in the same BB, END_TRY should be _before_ END_LOOP, because
LOOP is always before TRY if they are in the same BB. (TRY is placed in
the latest possible position, whereas LOOP is in the earliest possible position.)

[aheejin]

delete a newline

lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp

if (MI.getOpcode() == WebAssembly::END_TRY)
       AfterSet.insert(&MI);
 #endif
 
     // If there is a previously placed END_LOOP marker and its header is after
     // where TRY marker is, this loop is contained within the 'catch' part, so
     // the END_TRY marker should go after that. Otherwise, the whole try-catch
     // is contained within this loop, so the END_TRY should go before that.
     if (MI.getOpcode() == WebAssembly::END_LOOP) {
-      if (EndToBegin[&MI]->getParent()->getNumber() >= Header->getNumber())
+      // For a LOOP to be after TRY, LOOP's BB should be after TRY's BB; if they
+      // are in the same BB, LOOP is always before TRY.
+      if (EndToBegin[&MI]->getParent()->getNumber() > Header->getNumber())
         BeforeSet.insert(&MI);
 #ifndef NDEBUG
       else
         AfterSet.insert(&MI);
 #endif
     }
 
     // It is not possible for an END_BLOCK to be already in this block.

test/CodeGen/WebAssembly/cfg-stackify-eh.ll

catch.start:                                      ; preds = %catch.dispatch
   %2 = call i8* @llvm.wasm.get.exception(token %1)
   %3 = call i32 @llvm.wasm.get.ehselector(token %1)
   catchret from %1 to label %try.cont
 
 try.cont:                                         ; preds = %catch.start, %bb4, %bb3, %bb2
   ret void
 }
 
+; Tests if try/end_try markers are placed correctly wrt loop/end_loop markers,
+; when try and loop markers are in the same BB and end_try and end_loop are in
+; another BB.
+; CHECK: loop
+; CHECK:   try
+; CHECK:     call      foo
+; CHECK:   catch
+; CHECK:   end_try
+; CHECK: end_loop
+define void @test4(i32* %p) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+entry:
+  store volatile i32 0, i32* %p
+  br label %loop
+
+loop:                                             ; preds = %try.cont, %entry
+  store volatile i32 1, i32* %p
+  invoke void @foo()
+          to label %try.cont unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %loop
+  %0 = catchswitch within none [label %catch.start] unwind to caller
+
+catch.start:                                      ; preds = %catch.dispatch
+  %1 = catchpad within %0 [i8* null]
+  %2 = call i8* @llvm.wasm.get.exception(token %1)
+  %3 = call i32 @llvm.wasm.get.ehselector(token %1)
+  catchret from %1 to label %try.cont
+
+try.cont:                                         ; preds = %catch.start, %loop
+  br label %loop
+}
+
 declare void @foo()
 declare void @bar()
 declare i32 @__gxx_wasm_personality_v0(...)
 declare i8* @llvm.wasm.get.exception(token)
 declare i32 @llvm.wasm.get.ehselector(token)
 declare void @llvm.wasm.rethrow.in.catch()
 declare i32 @llvm.eh.typeid.for(i8*)
 declare i8* @__cxa_begin_catch(i8*)
 declare void @__cxa_end_catch()
 declare void @__clang_call_terminate(i8*)
 declare void @_ZSt9terminatev()