[WebAssembly] Treat __cxa_end_catch not longjmpable in Emscripten SjLj

[aheejin]

Summary

In D117610 we treated __cxa_end_catch longjmpable even though it was
not to make unwind destination relationships correct. But we only need
to do this in Wasm SjLj, and doing this in Emscripten SjLj does not make
the code incorrect but add unnecessary invokes. This CL treats
__cxa_end_catch longjmpable only in Wasm SjLj.

[aheejin]

llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj.ll

50–52

This was just moved to add the CHECK-NOT line above

llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp

if (CalleeName == "__resumeException" || CalleeName == "llvm_eh_typeid_for" ||
     return false;
 
   // __cxa_find_matching_catch_N functions cannot longjmp
   if (Callee->getName().startswith("__cxa_find_matching_catch_"))
     return false;
 
   // Exception-catching related functions
   //
-  // We intentionally excluded __cxa_end_catch here even though it surely cannot
-  // longjmp, in order to maintain the unwind relationship from all existing
-  // catchpads (and calls within them) to catch.dispatch.longjmp.
+  // We intentionally treat __cxa_end_catch longjmpable in Wasm SjLj even though
+  // it surely cannot longjmp, in order to maintain the unwind relationship from
+  // all existing catchpads (and calls within them) to catch.dispatch.longjmp.
   //
   // In Wasm EH + Wasm SjLj, we
   // 1. Make all catchswitch and cleanuppad that unwind to caller unwind to
   //    catch.dispatch.longjmp instead
   // 2. Convert all longjmpable calls to invokes that unwind to
   //    catch.dispatch.longjmp
   // But catchswitch BBs are removed in isel, so if an EH catchswitch (generated
   // from an exception)'s catchpad does not contain any calls that are converted
static bool canLongjmp(const Value *Callee) {
   // result.
   //
   // Every catchpad generated by Wasm C++ contains __cxa_end_catch, so we
   // intentionally treat it as longjmpable to work around this problem. This is
   // a hacky fix but an easy one.
   //
   // The comment block in findWasmUnwindDestinations() in
   // SelectionDAGBuilder.cpp is addressing a similar problem.
+  if (CalleeName == "__cxa_end_catch")
+    return WebAssembly::WasmEnableSjLj;
   if (CalleeName == "__cxa_begin_catch" ||
       CalleeName == "__cxa_allocate_exception" || CalleeName == "__cxa_throw" ||
       CalleeName == "__clang_call_terminate")
     return false;
 
   // std::terminate, which is generated when another exception occurs while
   // handling an exception, cannot longjmp.
   if (CalleeName == "_ZSt9terminatev")

llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj.ll

 ; CHECK-NEXT: %[[CMP:.*]] = and i1 %[[CMP0]], %[[CMP1]]
 ; CHECK-NEXT: br i1 %[[CMP]], label %if.then1, label %if.else1
 
 ; This is exception checking part. %if.else1 leads here
 ; CHECK:    entry.split.split.split:
 ; CHECK-NEXT: %[[CMP:.*]] = icmp eq i32 %__THREW__.val, 1
 ; CHECK-NEXT: br i1 %[[CMP]], label %lpad, label %try.cont
 
-; longjmp checking part
-; CHECK:    if.then1:
-; CHECK:      call i32 @testSetjmp
-
+; CHECK:    lpad:
 lpad:                                             ; preds = %entry
   %0 = landingpad { i8*, i32 }
           catch i8* null
   %1 = extractvalue { i8*, i32 } %0, 0
   %2 = extractvalue { i8*, i32 } %0, 1
+; CHECK-NOT:  call {{.*}} void @__invoke_void(void ()* @__cxa_end_catch)
   %3 = call i8* @__cxa_begin_catch(i8* %1) #2
   call void @__cxa_end_catch()
   br label %try.cont
 
 try.cont:                                         ; preds = %lpad, %entry
   ret void
+
+; longjmp checking part
+; CHECK:    if.then1:
+; CHECK:      call i32 @testSetjmp
 }
 
 ; @foo can either throw an exception or longjmp. Because this function doesn't
 ; have any setjmp calls, we only handle exceptions in this function. But because
 ; sjlj is enabled, we check if the thrown value is longjmp and if so rethrow it
 ; by calling @emscripten_longjmp.
 define void @rethrow_longjmp() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
 ; CHECK-LABEL: @rethrow_longjmp