[Coroutines] Do not add allocas for retcon coroutines

Same as for async-style lowering, if there are no resume points in a
function, the coroutine frame pointer will be replaced by an undef,
making all accesses to the frame undefinde behavior.

Fix this by not adding allocas to the coroutine frame if there are no
resume points.

Differential Revision: https://reviews.llvm.org/D137866

Author: Flakebi

llvm/lib/Transforms/Coroutines/CoroFrame.cpp

@@ -2732,7 +2732,7 @@ void coro::buildCoroutineFrame(Function &F, Shape &Shape) {
       Shape.ABI != coro::ABI::RetconOnce)
     sinkLifetimeStartMarkers(F, Shape, Checker);
 
-  if (Shape.ABI != coro::ABI::Async || !Shape.CoroSuspends.empty())
+  if (Shape.ABI == coro::ABI::Switch || !Shape.CoroSuspends.empty())
     collectFrameAllocas(F, Shape, Checker, FrameData.Allocas);
   LLVM_DEBUG(dumpAllocas(FrameData.Allocas));
 

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

@@ -130,12 +130,17 @@ cleanup:
 define i8* @nosuspend(i8* %buffer, i32 %n) {
 ; CHECK-LABEL: @nosuspend(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    unreachable
+; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    store i32 [[N:%.*]], i32* [[A]], align 4
+; CHECK-NEXT:    call void @use_var_ptr(i32* nonnull [[A]])
+; CHECK-NEXT:    [[AL:%.*]] = load i32, i32* [[A]], align 4
+; CHECK-NEXT:    call void @use_var(i32 [[AL]])
+; CHECK-NEXT:    ret i8* null
 ;
 ; CORO-LABEL: @nosuspend(
 ; CORO-NEXT:  entry:
 ; CORO-NEXT:    [[FRAMEPTR:%.*]] = bitcast i8* undef to %nosuspend.Frame*
-; CORO-NEXT:    [[A:%.*]] = getelementptr inbounds [[NOSUSPEND_FRAME:%.*]], %nosuspend.Frame* [[FRAMEPTR]], i32 0, i32 0
+; CORO-NEXT:    [[A:%.*]] = alloca i32, align 4
 ; CORO-NEXT:    store i32 [[N:%.*]], i32* [[A]], align 4
 ; CORO-NEXT:    call void @use_var_ptr(i32* [[A]])
 ; CORO-NEXT:    [[AL:%.*]] = load i32, i32* [[A]], align 4