[PATCH] D12353: [WinEH] Update coloring to handle nested cases cleanly

[Joseph Tremoulet via llvm-commits]

JosephTremoulet added inline comments.

================
Comment at: test/CodeGen/WinEH/wineh-cloning.ll:269-270
@@ +268,4 @@
+; %inner is a cleanup which appears both as a child of
+; %left and as a child of %right.  Since statically we
+; need each funclet to have a single parent, we need to
+; clone the entire %inner funclet so we can have one
----------------
JosephTremoulet wrote:
> majnemer wrote:
> > When you say each funclet needs to have a single parent, do you mean that it must have a single non-invoke predecessor?  It will be quite common for a set of invokes in a try-block to have the same unwind destination.
> I mean that all of its invoke predecessors, after cloning, must be in the same funclet.
This might be a more illustrative example:
```
define void @foo() personality etc {
entry:
  invoke void @f()
    to label %exit unwind label %funcletA
funcletA:
  %A = catchpad []
         to label %bodyA unwind label %endpad
bodyA:
  invoke void @g()
    to label %invoke.cont unwind label %endpad
invoke.cont:
  invoke void @h()
    to label %retA unwind label %funcletB
retA:
  catchret %A to label %exit
funcletB:
  %B = cleanuppad []
  call void @i()
  cleanupret %B unwind to caller
exit:
  ret void
}
```

Say we enter `@foo()` and generate a stack frame for it, then the call to `@f()` raises an exception that is handled by `funcletA`, so the runtime calls `funcletA` (and we generate a stack frame for it).  Now there are two `invoke`s in `funcletA`, both of which are handled by `funcletB`, but if the call to `@g()` faults the `endpad` indicates that the runtime needs to unwind out of `funcletA` before calling `funcletB`, whereas if the call to `@h()` faults then the runtime is supposed to invoke `funcletB` while `funcletA`'s frame is still on the stack.  I don't think we can expect WinEH targets to support encoding and executing that arrangement without making two copies of `funcletB`.
(in the case where the call to `@h()` faults, the `cleanupret` that unwinds to caller instead of unwinding to `%retA` is UB, so we'd want to replace it with `unreachable` in that copy of `funcletB`, but I think we still want a copy just in case `@h()` does not return dynamically and so the program never executes UB; similarly, if the input already had `unreachable` there instead of a `cleanupret`, we wouldn't know statically which reporting is correct for `funcletB` and so I'd think would want two copies of it)


http://reviews.llvm.org/D12353