[PATCH] D97915: [Coroutines] Handle overaligned frame allocation

[John McCall via Phabricator via cfe-commits]

rjmccall added inline comments.


================
Comment at: clang/lib/CodeGen/CGBuiltin.cpp:4450
+    Value *Extra = Builder.CreateSelect(Cmp, Diff, Zero);
+    return RValue::get(Builder.CreateAdd(SizeCall, Extra));
   }
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Okay, so you're implicitly increasing the coroutine size to allow you to round up to get an aligned frame.  But how do you round back down to get the actual pointer that you need to delete?  This just doesn't work.

You really ought to just be using the aligned `operator new` instead when the required alignment is too high.  If that means checking the alignment "dynamically" before calling `operator new` / `operator delete`, so be it.  In practice, it will not be dynamic because lowering will replace the `coro.align` call with a constant, at which point the branch will be foldable.

I don't know what to suggest if the aligned `operator new` isn't reliably available on the target OS.  You could outline a function to pick the best allocator/deallocator, I suppose.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D97915/new/

https://reviews.llvm.org/D97915