[PATCH] Assembly/bitcode support for GenericDebugNode

Duncan P. N. Exon Smith dexonsmith at apple.com
Mon Feb 2 14:21:02 PST 2015

> On 2015-Feb-02, at 13:51, Adrian Prantl <aprantl at apple.com> wrote:
>> On Feb 2, 2015, at 1:34 PM, Frédéric Riss <friss at apple.com> wrote:
>>> On Feb 2, 2015, at 12:55 PM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
>>> Add assembly/bitcode support to `GenericDebugNode`.  There are two
>>> things I need reviewed here (although other comments are obviously
>>> welcome):
>>> - The first three patches add a `dwarf::getTag()` to complement
>>>  `dwarf::TagString()`.  There's a small functionality change in the
>>>  first patch I want confirmation on: `dwarf::TagString()` will return
>>>  `nullptr` for `DW_TAG_lo_user` (and related non-tags).  This
>>>  constant is not really a DWARF tag; it's just a marker for the first
>>>  recommended user-defined tag).  Stringifying it seems wrong (and
>>>  would conflict with stringifying a user-defined tag of the same
>>>  number).
>> The 3 patches SGTM, a couple of questions/remarks though:
>> I agree that stringifying lo_user and friends makes no real sense as we
>> are using the TagString function to pretty print actual dwarf data. Not that
>> it matters today as we have no such extension registered.
>> Why would you want to ever accept them as input? I really don’t see a
>> reason, but given you’ve introduced a special case for them, you really
>> must need them.
> Derived tools like llvm-dwarfdump should be able to handle DWARF generated by other compilers and should probably print something like DW_TAG_user(0x1234) when it encounters an unknown tag.

That makes sense, but it doesn't affect `getTag()`, since that's
unstringifying things.  And it doesn't seem to fit into `TagString()` too
well either.  I think that logic should probably live in llvm-dwarfdump.

> -- adrian
>> Is there a way to cleanly generate the enum in the Dwarf.h file from the
>> .def file also? This way there would be only one source of tag definitions.
>> (This would me having Dwarf.def as an exported header, which is quite
>> ugly). At least add a comment to the header that anything added to the
>> enum should be added to the def file.
>> Fred
>>> - The fourth patch adds assembly/bitcode support, and the fifth
>>>  improves it by using `dwarf::getTag()`.  Here's the resulting
>>>  syntax:
>>>      !0 = !GenericDebugNode(tag: DW_TAG_entry_point,
>>>                             header: "some\00header",
>>>                             operands: {!1, !2, !7})
>>>  This shouldn't be surprising (or a departure from the plan of
>>>  record), but officially I need every assembly change reviewed
>>>  pre-commit.
>>> Note that this commit doesn't actually move `GenericDebugNode` into
>>> place (and that's not the next step; more below for those interested).
>>> (An extended side-note:
>>> I've been sitting on these patches for a while, kind of stumped on the
>>> best way to stage the rest of the work here.
>>> Originally, I'd planned to move `GenericDebugNode` in underneath the
>>> `DIDescriptor` classes right after this patch series.  This would have
>>> required updating all the testcases to use it, only to subsequently
>>> update every line *again* as I implemented the more specialized nodes
>>> (making schema changes along the way).
>>> Instead I'll be proceeding as follows: add specialized nodes that match
>>> the current schema, add assembly/bitcode support for them (I have
>>> out-of-tree patches that get to here), move them all underneath the
>>> `DIDescriptor` hierarchy (only requiring each line to be updated
>>> *once*), and then start hacking the schema once they're in place.
>>> The new approach minimizes testcase churn, and (perhaps more
>>> importantly) better separates the infrastructure changes (which are
>>> rather mechanical) from the schema changes (which need more careful
>>> consideration).)
>>> <0001-Support-Stop-stringifying-DW_TAG_-lo-hi-_user.patch><0002-Support-Re-implement-dwarf-TagString-using-a-.def-fi.patch><0003-Support-Add-string-unsigned-mapping-for-DW_TAG.patch><0004-IR-Assembly-and-bitcode-for-GenericDebugNode.patch><0005-AsmParser-Recognize-DW_TAG_-constants.patch>

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