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

[David Majnemer via llvm-commits]

majnemer 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:
> JosephTremoulet wrote:
> > 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)
> sigh... insert
> ```
> endpad:
>   catchendpad unwind label %funcletB
> ```
> somewhere in `@foo` in the previous example.
Our langref describes `catchendpad` using the following language:
>  The unwind target of invokes between a catchpad and a corresponding catchret must be its catchendpad or an inner EH pad.


It was my understanding that all invokes in a `catchpad` funclet must transitively unwind to the `catchendpad`.

Your example would violate this because the `catchret` in `funcletB` uses `unwinds to caller`.


http://reviews.llvm.org/D12353