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Diffstat (limited to 'llvm/docs')
| -rw-r--r-- | llvm/docs/Coroutines.rst | 85 |
1 files changed, 67 insertions, 18 deletions
diff --git a/llvm/docs/Coroutines.rst b/llvm/docs/Coroutines.rst index 0e7cde7aa38..d330d715f7c 100644 --- a/llvm/docs/Coroutines.rst +++ b/llvm/docs/Coroutines.rst @@ -110,7 +110,7 @@ The LLVM IR for this coroutine looks like this: 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 @@ store the current value produced by a coroutine. 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 @@ A frontend should emit exactly one `coro.id` intrinsic per coroutine. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ :: - 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. + +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 -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. + 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: |
