transform (coroutines): fix memory corruption for tail calls that reference stack allocations

This change fixes a bug in which `alloca` memory lifetimes would not extend past the suspend of an asynchronous tail call.
This would typically manifest as memory corruption, and could happen with or without normal suspending calls within the function.

transform/testdata/coroutines.ll

@@ -86,11 +86,43 @@ entry:
 }
 
 ; Normal function which should not be transformed.
-define void @doNothing(i8*, i8*) {
+define void @doNothing(i8*, i8* %parentHandle) {
 entry:
   ret void
 }
 
+; Regression test: ensure that a tail call does not destroy the frame while it is still in use.
+; Previously, the tail-call lowering transform would branch to the cleanup block after usePtr.
+; This caused the lifetime of %a to be incorrectly reduced, and allowed the coroutine lowering transform to keep %a on the stack.
+; After a suspend %a would be used, resulting in memory corruption.
+define i8 @coroutineTailRegression(i8*, i8* %parentHandle) {
+entry:
+  %a = alloca i8
+  store i8 5, i8* %a
+  %val = call i8 @usePtr(i8* %a, i8* undef, i8* null)
+  ret i8 %val
+}
+
+; Regression test: ensure that stack allocations alive during a suspend end up on the heap.
+; This used to not be transformed to a coroutine, keeping %a on the stack.
+; After a suspend %a would be used, resulting in memory corruption.
+define i8 @allocaTailRegression(i8*, i8* %parentHandle) {
+entry:
+  %a = alloca i8
+  call void @sleep(i64 1000000, i8* undef, i8* null)
+  store i8 5, i8* %a
+  %val = call i8 @usePtr(i8* %a, i8* undef, i8* null)
+  ret i8 %val
+}
+
+; usePtr uses a pointer after a suspend.
+define i8 @usePtr(i8*, i8*, i8* %parentHandle) {
+entry:
+  call void @sleep(i64 1000000, i8* undef, i8* null)
+  %val = load i8, i8* %0
+  ret i8 %val
+}
+
 ; Goroutine that sleeps and does nothing.
 ; Should be a void tail call.
 define void @sleepGoroutine(i8*, i8* %parentHandle) {