[CoroSplit][NewPM] Don't call LazyCallGraph functions to split when no clones

[aeubanks]

Summary

Apparently there can be no clones, as happens in
coro-retcon-unreachable.ll.

The alternative is to allow no split functions in
addSplitRefRecursiveFunctions(), but it seems better to have the caller
make sure it's not accidentally splitting no functions out.

Depends on D94257.

[rnk]

lgtm

llvm/lib/Transforms/Coroutines/CoroSplit.cpp

if (!Shape.CoroBegin)
     return;
 
   for (llvm::AnyCoroEndInst *End : Shape.CoroEnds) {
     auto &Context = End->getContext();
     End->replaceAllUsesWith(ConstantInt::getFalse(Context));
     End->eraseFromParent();
   }
 
+  if (!Clones.empty()) {
     switch (Shape.ABI) {
     case coro::ABI::Switch:
-    // Each clone in the Switch lowering is independent of the other clones. Let
-    // the LazyCallGraph know about each one separately.
+      // Each clone in the Switch lowering is independent of the other clones.
+      // Let the LazyCallGraph know about each one separately.
       for (Function *Clone : Clones)
         CG.addSplitFunction(N.getFunction(), *Clone);
       break;
     case coro::ABI::Async:
     case coro::ABI::Retcon:
     case coro::ABI::RetconOnce:
       // Each clone in the Async/Retcon lowering references of the other clones.
       // Let the LazyCallGraph know about all of them at once.
       CG.addSplitRefRecursiveFunctions(N.getFunction(), Clones);
       break;
     }
 
     // Let the CGSCC infra handle the changes to the original function.
     updateCGAndAnalysisManagerForCGSCCPass(CG, C, N, AM, UR, FAM);
+  }
 
   // Do some cleanup and let the CGSCC infra see if we've cleaned up any edges
   // to the split functions.
   postSplitCleanup(N.getFunction());
   updateCGAndAnalysisManagerForFunctionPass(CG, C, N, AM, UR, FAM);
 }
 
 // When we see the coroutine the first time, we insert an indirect call to a

llvm/test/Transforms/Coroutines/coro-retcon-unreachable.ll

 ; RUN: opt < %s -coro-early -coro-split -S | FileCheck %s
+; RUN: opt < %s -passes='function(coro-early),cgscc(coro-split)' -S | FileCheck %s
 target datalayout = "E-p:64:64"
 
 %swift.type = type { i64 }
 %swift.opaque = type opaque
 %T4red215EmptyCollectionV = type opaque
 %TSi = type <{ i64 }>
 
 define hidden swiftcc { i8*, %swift.opaque* } @no_suspends(i8* %buffer, i64 %arg) #1 {