[coroutines] Add handling for unwind coro.ends
Summary:
The purpose of coro.end intrinsic is to allow frontends to mark the cleanup and
other code that is only relevant during the initial invocation of the coroutine
and should not be present in resume and destroy parts.
In landing pads coro.end is replaced with an appropriate instruction to unwind to
caller. The handling of coro.end differs depending on whether the target is
using landingpad or WinEH exception model.
For landingpad based exception model, it is expected that frontend uses the
`coro.end`_ intrinsic as follows:
```
ehcleanup:
%InResumePart = call i1 @llvm.coro.end(i8* null, i1 true)
br i1 %InResumePart, label %eh.resume, label %cleanup.cont
cleanup.cont:
; rest of the cleanup
eh.resume:
%exn = load i8*, i8** %exn.slot, align 8
%sel = load i32, i32* %ehselector.slot, align 4
%lpad.val = insertvalue { i8*, i32 } undef, i8* %exn, 0
%lpad.val29 = insertvalue { i8*, i32 } %lpad.val, i32 %sel, 1
resume { i8*, i32 } %lpad.val29
```
The `CoroSpit` pass replaces `coro.end` with ``True`` in the resume functions,
thus leading to immediate unwind to the caller, whereas in start function it
is replaced with ``False``, thus allowing to proceed to the rest of the cleanup
code that is only needed during initial invocation of the coroutine.
For Windows Exception handling model, a frontend should attach a funclet bundle
referring to an enclosing cleanuppad as follows:
```
ehcleanup:
%tok = cleanuppad within none []
%unused = call i1 @llvm.coro.end(i8* null, i1 true) [ "funclet"(token %tok) ]
cleanupret from %tok unwind label %RestOfTheCleanup
```
The `CoroSplit` pass, if the funclet bundle is present, will insert
``cleanupret from %tok unwind to caller`` before
the `coro.end`_ intrinsic and will remove the rest of the block.
Reviewers: majnemer
Reviewed By: majnemer
Subscribers: llvm-commits, mehdi_amini
Differential Revision: https://reviews.llvm.org/D25543
llvm-svn: 297223
diff --git a/llvm/docs/Coroutines.rst b/llvm/docs/Coroutines.rst
index 0e7cde7..d330d71 100644
--- a/llvm/docs/Coroutines.rst
+++ b/llvm/docs/Coroutines.rst
@@ -110,7 +110,7 @@
call void @free(i8* %mem)
br label %suspend
suspend:
- call void @llvm.coro.end(i8* %hdl, i1 false)
+ %unused = call i1 @llvm.coro.end(i8* %hdl, i1 false)
ret i8* %hdl
}
@@ -440,7 +440,7 @@
call void @free(i8* %mem)
br label %suspend
suspend:
- call void @llvm.coro.end(i8* %hdl, i1 false)
+ %unused = call i1 @llvm.coro.end(i8* %hdl, i1 false)
ret i8* %hdl
}
@@ -955,41 +955,90 @@
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
::
- declare void @llvm.coro.end(i8* <handle>, i1 <unwind>)
+ declare i1 @llvm.coro.end(i8* <handle>, i1 <unwind>)
Overview:
"""""""""
The '``llvm.coro.end``' marks the point where execution of the resume part of
-the coroutine should end and control returns back to the caller.
+the coroutine should end and control should return to the caller.
Arguments:
""""""""""
-The first argument should refer to the coroutine handle of the enclosing coroutine.
+The first argument should refer to the coroutine handle of the enclosing
+coroutine. A frontend is allowed to supply null as the first parameter, in this
+case `coro-early` pass will replace the null with an appropriate coroutine
+handle value.
The second argument should be `true` if this coro.end is in the block that is
-part of the unwind sequence leaving the coroutine body due to exception prior to
-the first reaching any suspend points, and `false` otherwise.
+part of the unwind sequence leaving the coroutine body due to an exception and
+`false` otherwise.
Semantics:
""""""""""
-The `coro.end`_ intrinsic is a no-op during an initial invocation of the
-coroutine. When the coroutine resumes, the intrinsic marks the point when
-coroutine need to return control back to the caller.
+The purpose of this intrinsic is to allow frontends to mark the cleanup and
+other code that is only relevant during the initial invocation of the coroutine
+and should not be present in resume and destroy parts.
-This intrinsic is removed by the CoroSplit pass when a coroutine is split into
-the start, resume and destroy parts. In start part, the intrinsic is removed,
-in resume and destroy parts, it is replaced with `ret void` instructions and
+This intrinsic is lowered when a coroutine is split into
+the start, resume and destroy parts. In the start part, it is a no-op,
+in resume and destroy parts, it is replaced with `ret void` instruction and
the rest of the block containing `coro.end` instruction is discarded.
-
In landing pads it is replaced with an appropriate instruction to unwind to
-caller.
+caller. The handling of coro.end differs depending on whether the target is
+using landingpad or WinEH exception model.
-A frontend is allowed to supply null as the first parameter, in this case
-`coro-early` pass will replace the null with an appropriate coroutine handle
-value.
+For landingpad based exception model, it is expected that frontend uses the
+`coro.end`_ intrinsic as follows:
+
+.. code-block:: llvm
+
+ ehcleanup:
+ %InResumePart = call i1 @llvm.coro.end(i8* null, i1 true)
+ br i1 %InResumePart, label %eh.resume, label %cleanup.cont
+
+ cleanup.cont:
+ ; rest of the cleanup
+
+ eh.resume:
+ %exn = load i8*, i8** %exn.slot, align 8
+ %sel = load i32, i32* %ehselector.slot, align 4
+ %lpad.val = insertvalue { i8*, i32 } undef, i8* %exn, 0
+ %lpad.val29 = insertvalue { i8*, i32 } %lpad.val, i32 %sel, 1
+ resume { i8*, i32 } %lpad.val29
+
+The `CoroSpit` pass replaces `coro.end` with ``True`` in the resume functions,
+thus leading to immediate unwind to the caller, whereas in start function it
+is replaced with ``False``, thus allowing to proceed to the rest of the cleanup
+code that is only needed during initial invocation of the coroutine.
+
+For Windows Exception handling model, a frontend should attach a funclet bundle
+referring to an enclosing cleanuppad as follows:
+
+.. code-block:: text
+
+ ehcleanup:
+ %tok = cleanuppad within none []
+ %unused = call i1 @llvm.coro.end(i8* null, i1 true) [ "funclet"(token %tok) ]
+ cleanupret from %tok unwind label %RestOfTheCleanup
+
+The `CoroSplit` pass, if the funclet bundle is present, will insert
+``cleanupret from %tok unwind to caller`` before
+the `coro.end`_ intrinsic and will remove the rest of the block.
+
+The following table summarizes the handling of `coro.end`_ intrinsic.
+
++--------------------------+-------------------+-------------------------------+
+| | In Start Function | In Resume/Destroy Functions |
++--------------------------+-------------------+-------------------------------+
+|unwind=false | nothing |``ret void`` |
++------------+-------------+-------------------+-------------------------------+
+| | WinEH | nothing |``cleanupret unwind to caller``|
+|unwind=true +-------------+-------------------+-------------------------------+
+| | Landingpad | nothing | nothing |
++------------+-------------+-------------------+-------------------------------+
.. _coro.suspend:
.. _suspend points: