[PATCH] D75338: [Coroutines] Use dbg.declare for frame variables

[Brian Gesiak via Phabricator via llvm-commits]

modocache added inline comments.


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Comment at: llvm/test/Transforms/Coroutines/coro-debug.ll:29-30
 sw.bb:                                            ; preds = %entry
+  call void @llvm.dbg.declare(metadata i32* %x.addr, metadata !12, metadata !13), !dbg !14
+  call void @llvm.dbg.declare(metadata i8** %coro_hdl, metadata !15, metadata !13), !dbg !16
   br label %sw.epilog, !dbg !18
----------------
jmorse wrote:
> Why are these dbg.declares moving down -- is it to check that they're moved into the entry block later on?
Right, sorry for the confusion. I mention in the commit message:

> The existing coro-debug.ll test case is also modified to reflect the locations at which Clang actually places calls to 'dbg.declare', and additional checks are added to ensure this patch works as intended in that example as well.

This patch adds the CHECK below that the `llvm.dbg.declare` will correctly appear in the coroutine funclet `f.resume`, which makes it possible for debuggers to "find" the variable `x` when stopped in a resumed coroutine function.

But, the logic in the patch works on the assumption that the original `llvm.dbg.declare` describing the variable `x` appears not in the function's entry block (where Clang places it in a non-coroutine function), but instead in the basic block that represents the coroutine's resumption after its implicit "initial suspend" point (where Clang places it in a coroutine function, since Clang first codegen's the `br` instructions for the implicit suspend point, and then codegen's the function's body).

These `dbg.declare` don't need to be moved like this, but if they aren't, then the added CHECK below won't succeed -- the patch ensures that `dbg.declare` are migrated to coroutine funclets, but specifically only when dealing with IR in the form that Clang generates it.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D75338/new/

https://reviews.llvm.org/D75338