[WebAssembly] Make sure EH pads are preferred in sorting

[aheejin]

Summary

In CFGSort, we try to make EH pads have higher priorities as soon as
they are ready to be sorted, to prevent creation of unwind destination
mismatches in CFGStackify. We did that by making priority queues'
comparison function prefer EH pads, but it was possible for an EH pad
to be popped from Preferred queue and then not sorted immediately and
enter Ready queue instead in a certain condition. This patch makes
sure that special condition does not consider EH pads as its candidates.

llvm/lib/Target/WebAssembly/WebAssemblyCFGSort.cpp

while (!Preferred.empty()) {
           !MDT.dominates(Entries.back().TheRegion->getHeader(), Next)) {
         Entries.back().Deferred.push_back(Next);
         Next = nullptr;
         continue;
       }
       // If Next was originally ordered before MBB, and it isn't because it was
       // loop-rotated above the header, it's not preferred.
       if (Next->getNumber() < MBB->getNumber() &&
+          (WasmDisableEHPadSort || !Next->isEHPad()) &&
           (!R || !R->contains(Next) ||
            R->getHeader()->getNumber() < Next->getNumber())) {
         Ready.push(Next);
         Next = nullptr;
         continue;
       }
       break;
     }

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

catch.start1:                                     ; preds = %catch.dispatch1
   %9 = call i8* @__cxa_begin_catch(i8* %7) [ "funclet"(token %6) ]
   call void @__cxa_end_catch() [ "funclet"(token %6) ]
   catchret from %6 to label %try.cont
 
 try.cont:                                         ; preds = %catch.start1, %catch.start0, %bb1
   ret void
 }
 
+; In CFGSort, EH pads should be sorted as soon as it is available and
+; 'Preferred' queue and should NOT be entered into 'Ready' queue unless we are
+; in the middle of sorting another region that does not contain the EH pad. In
+; this example, 'catch.start' should be sorted right after 'if.then' is sorted
+; (before 'cont' is sorted) and there should not be any unwind destination
+; mismatches in CFGStackify.
+
+; NOOPT: block
+; NOOPT:   try
+; NOOPT:     call      foo
+; NOOPT:   catch
+; NOOPT:   end_try
+; NOOPT:   call      foo
+; NOOPT: end_block
+; NOOPT: return
+define void @test9(i32 %arg) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+entry:
+  %tobool = icmp ne i32 %arg, 0
+  br i1 %tobool, label %if.then, label %if.end
+
+catch.dispatch:                                   ; preds = %if.then
+  %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)
+  %4 = call i8* @__cxa_begin_catch(i8* %2) [ "funclet"(token %1) ]
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %if.end
+
+if.then:                                          ; preds = %entry
+  invoke void @foo()
+          to label %cont unwind label %catch.dispatch
+
+cont:                                             ; preds = %if.then
+  call void @foo()
+  br label %if.end
+
+if.end:                                           ; preds = %cont, %catch.start, %entry
+  ret void
+}
+
 declare void @foo()
 declare void @bar()
 declare i32 @baz()
 ; Function Attrs: nounwind
 declare void @nothrow(i32) #0
 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()
 
 attributes #0 = { nounwind }