Relax restriction on fallthrough coro.end

Author: NewSigma

llvm/include/llvm/Transforms/Coroutines/CoroInstr.h

@@ -682,7 +682,7 @@ class AnyCoroEndInst : public IntrinsicInst {
   enum { FrameArg, UnwindArg, TokenArg };
 
 public:
-  bool isFallthrough() const { return !isUnwind() && user_empty(); }
+  bool isFallthrough() const { return !isUnwind(); }
   bool isUnwind() const {
     return cast<Constant>(getArgOperand(UnwindArg))->isOneValue();
   }

llvm/lib/Transforms/Coroutines/Coroutines.cpp

@@ -259,18 +259,6 @@ void coro::Shape::analyze(Function &F,
 
         if (CoroEnds.back()->isUnwind())
           HasUnwindCoroEnd = true;
-
-        if (CoroEnds.back()->isFallthrough() && isa<CoroEndInst>(II)) {
-          // Make sure that the fallthrough coro.end is the first element in the
-          // CoroEnds vector.
-          // Note: I don't think this is neccessary anymore.
-          if (CoroEnds.size() > 1) {
-            if (CoroEnds.front()->isFallthrough())
-              report_fatal_error(
-                  "Only one coro.end can be marked as fallthrough");
-            std::swap(CoroEnds.front(), CoroEnds.back());
-          }
-        }
         break;
       case Intrinsic::coro_promise:
         assert(CoroPromise == nullptr &&

llvm/test/Transforms/Coroutines/coro-split-coroend.ll

@@ -28,13 +28,13 @@ entry:
 
 end:
   %InResume = call i1 @llvm.coro.end(ptr null, i1 false, token none)
-  br i1 %InResume, label %start, label %done
+  br i1 %InResume, label %resume, label %start
 
-start:
+resume:
   call void @a()
-  br label %done
+  br label %start
 
-done:
+start:
   call i1 @llvm.coro.end(ptr null, i1 false, token none)
   ret ptr %hdl
 }