[PATCH] D66746: [LiveDebugValues] Omit entry values for DBG_VALUEs with pre-existing expressions

[Paul Robinson via Phabricator via llvm-commits]

probinson added a comment.

In D66746#1647732 <https://reviews.llvm.org/D66746#1647732>, @aprantl wrote:

> > I have interpreted the size as meaning the byte size of the DWARF block that the operation will cover. Assuming that, at the time of running LiveDebugValues I don't think there is a good way to query the size of the block that the entry value will cover; we don't know that until we actually emit the DWARF, as far as I can tell. That is why I have assumed that a hard coded operand of 1 is emitted there, with the assumption that only simple register location descriptions are supported.
>
> I think it would be reasonable to use the number of opcodes in the DIExpression in LLVM IR and only substitute the number of bytes in AsmPrinter.


+1.  The DIExpression is more of an abstracted expression than a true DWARF expression, and even supports non-DWARF opcodes e.g. DW_OP_LLVM_convert.  We can't be treating this as the size of the final expression.


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