[clang] [llvm] [coro] Lower `llvm.coro.await.suspend.handle` to resume with tail call (PR #89751)

[Mircea Trofin via cfe-commits]

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@@ -1056,6 +1083,25 @@ void CoroCloner::create() {
   // Set up the new entry block.
   replaceEntryBlock();
 
+  // Turn symmetric transfers into musttail calls.
+  for (CallInst *ResumeCall : Shape.SymmetricTransfers) {
+    ResumeCall = cast<CallInst>(VMap[ResumeCall]);
+    ResumeCall->setCallingConv(NewF->getCallingConv());
+    if (TTI.supportsTailCallFor(ResumeCall)) {
+      // FIXME: Could we support symmetric transfer effectively without
+      // musttail?
+      ResumeCall->setTailCallKind(CallInst::TCK_MustTail);
+    }
+
+    // Put a 'ret void' after the call, and split any remaining instructions to
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mtrofin wrote:

if there are remaining instructions, this will silently elide them. I realize that there shouldn't be remaining instructions, but we could detect bugs like the PGO instrumentation + coro one (PR #71263) if that was asserted or WARNed or something more visible.

https://github.com/llvm/llvm-project/pull/89751