[PATCH] D67492: [DebugInfo] Add a DW_OP_LLVM_entry_value operation

Mon Sep 30 23:40:27 PDT 2019

djtodoro added inline comments.

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Comment at: llvm/docs/LangRef.rst:4789
   DWARF expression.
-  ``DW_OP_entry_value`` may appear after the ``LiveDebugValues`` pass.
+  ``DW_OP_LLVM_entry_value`` may appear after the ``LiveDebugValues`` pass.
   LLVM only supports entry values for function parameters
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dstenb wrote:
> aprantl wrote:
> > aprantl wrote:
> > > may appear -> is introduced by
> > The documentation currently doesn't make clear whether DW_OP_LLVM_entry_value considers the implicit SSA value bound by a dbg.value / the argument of a DBG_VALUE to be part of the entry value or the surrounding expression and/or whether it expects a hardcoded location such as DW_OP_breg0 inside the DW_OP_LLVM_entry_value. It also isn't clear whether DW_OP_LLVM_entry_value is only legal in MIR, or also in LLVM IR and what the semantics in LLVM IR are if it is allowed.
> > 
> > I think a few examples would go a long way here.
> I have now updated the text to hopefully make it more descriptive.
> 
> I have updated the documentation to say that the operation is only legal in MIR, mainly as the operation has not been tested in LLVM IR, and I personally don't see why anyone would want to emit it there. Any comments on that, @djtodoro and @NikolaPrica?
This looks nice! Thanks!

If we face situation where the entry value operation is useful for the LLVM IR we can revisit this, but at the moment I can not imagine such situation.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D67492/new/

https://reviews.llvm.org/D67492