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

Thu Sep 12 15:08:08 PDT 2019

aprantl added a comment.

Normally I would insist on a bitcode upgrade, but since this feature is so new I think we can skip that. However, because of bitcode compatability, we might want to get the semantics right from the start. Otherwise we might have to allocate a new opcode and implement an upgrade when we need to change it in the future.

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Comment at: llvm/lib/IR/DebugInfoMetadata.cpp:896
       // of following expression should be 1, because we support only
       // entry values of a simple register location.
       return I->get() == expr_op_begin()->get() && I->getArg(0) == 1 &&
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dstenb wrote:
> aprantl wrote:
> > Can someone remind me what the reason for this limitation was again? Do we still need it after this patch?
> I think that the main (or perhaps only?) reason for this limitation is that we, at emission, currently don't have a good way to calculate the size of the block that the entry value covers, and emit that size as a ULEB128 operand before the block. This patch will not change that.
I see. Could you please add this to the comment here, so it's clear why the restriction exists and how to lift it in the future?

Repository:
  rL LLVM

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  https://reviews.llvm.org/D67492/new/

https://reviews.llvm.org/D67492