[clang] 3661595 - [Coroutines] Special handle __builtin_coro_resume for final_suspend nothrow check

[Xun Li via cfe-commits]

Author: Xun Li
Date: 2020-06-25T10:49:50-07:00
New Revision: 366159566df3a980d3e34f3ec9609e77cdb4df8b

URL: https://github.com/llvm/llvm-project/commit/366159566df3a980d3e34f3ec9609e77cdb4df8b
DIFF: https://github.com/llvm/llvm-project/commit/366159566df3a980d3e34f3ec9609e77cdb4df8b.diff

LOG: [Coroutines] Special handle __builtin_coro_resume for final_suspend nothrow check

Summary:
In https://reviews.llvm.org/D82029 we added the conformance check that the expression co_await promise.final_suspend() should not potentially throw.
As part of this expression, in cases when the await_suspend() method of the final suspend awaiter returns a handle, __builtin_coro_resume could be called on the handle to immediately resume that coroutine.
__builtin_coro_resume is not declared with noexcept and it shouldn't. We need to special check this case here.

Reviewers: modocache, lewissbaker, junparser

Reviewed By: lewissbaker

Subscribers: modocache, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D82415

Added: 
    

Modified: 
    clang/lib/Sema/SemaCoroutine.cpp

Removed: 
    


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diff  --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index c8ca247aae83..6262f4b117d3 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -614,6 +614,17 @@ static void checkNoThrow(Sema &S, const Stmt *E,
     // In the case of dtor, the call to dtor is implicit and hence we should
     // pass nullptr to canCalleeThrow.
     if (Sema::canCalleeThrow(S, IsDtor ? nullptr : cast<Expr>(E), D)) {
+      if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
+        // co_await promise.final_suspend() could end up calling
+        // __builtin_coro_resume for symmetric transfer if await_suspend()
+        // returns a handle. In that case, even __builtin_coro_resume is not
+        // declared as noexcept and may throw, it does not throw _into_ the
+        // coroutine that just suspended, but rather throws back out from
+        // whoever called coroutine_handle::resume(), hence we claim that
+        // logically it does not throw.
+        if (FD->getBuiltinID() == Builtin::BI__builtin_coro_resume)
+          return;
+      }
       if (ThrowingDecls.empty()) {
         // First time seeing an error, emit the error message.
         S.Diag(cast<FunctionDecl>(S.CurContext)->getLocation(),