[LLVMdev] Questions before moving the new debug info hierarchy into place (original) (raw)

Duncan P. N. Exon Smith dexonsmith at apple.com
Fri Feb 20 11:14:14 PST 2015

On 2015-Feb-20, at 09:44, Frédéric Riss <friss at apple.com> wrote:

Speaking of deduplication of filenames. I think we discussed that in the early stages of your work, but I just wanted to make sure I remember correctly: the new debug hierarchy will allow to implement specific uniquing behavior, right? So we will be able to tweak MDFile to unique: !MDFile(filename: "path/to/file", directory: "/path/to/dir") !MDFile(filename: "to/file", directory: "/path/to/dir/path") into the same object? I did some work in this area and in the current form it’s not really possible to do cleanly (don’t remember the details here, but I know punted it till we get smart uniquing capability).

IIRC, there was some talk about how the DWARF spec requires that references to a directory need to be the CWD of the compiler.

It's not clear to me which references need that, but I guess we need to sort out exactly what the requirements are so we know which way to canonicalize things. I wonder if this only matters for DW_TAG_compile_unit? If so, we could canonicalize freely everywhere else. (For example, we could store a path: node everywhere (dropping the filename/directory distinction, or canonicalizing it to basename/dirname, etc.), and add a cwd: to the compile unit.)

David also pointed out (in a previous thread about this) that the frontend (or DIBuilder) might be the right location for canonicalization. Certainly, we couldn't canonicalize .. references without access to the filesystem (at least not on POSIX platforms), but maybe we don't care about that anyway?

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