[COFF] Assign unique identifiers to ObjFiles from LTO

[rnk]

Summary

Use the unique filenames that are used when /lldsavetemps is passed.
After this change, module names for LTO blobs in PDBs will be unique.

Revert some changes from 1e0b158db (2017) that are no longer necessary
after removing MSVC LTO support.

[rnk]

• fix bug with lto object cache

[MaskRay]

Use the unique filenames that are used when /lldsavetemps is passed.

Is this for debug convenience? (llvm-pdbutil dump output) Or required by some tools?

lld/COFF/LTO.cpp

210

When can objBuf be empty?

lld/test/COFF/pdb-thinlto.ll

3

%T is deprecated

https://llvm.org/docs/CommandGuide/lit.html

You can use %t.dir or just %t

; RUN: rm -rf %t.dir
; RUN: mkdir %t.dir
; RUN: cd %t.dir

Then you can remove one rm -Rf below

15

Not sure whether COFF wants to adopt this convention: in lld/ELF and some binary utilities, we start to use ## (translated to .ll: ;; ) for comments, # (; ) for RUN/CHECK lines.

This convention makes comments slightly easier to be discovered.

32

Delete trailing spaces (invisible on Phabricator)

34

You may indent Mod 0000 by 2 spaces to reflect the actual output... but why does llvm-pdbutil print two spaces only for Mod 0000?

lld/test/COFF/weak-external.test

8–9

Nit: add 5 spaces to make CHECK1 content aligned with the next line.

lld/test/COFF/weak-external3.test

9–10

Nit: add 5 spaces to make CHECK1 content aligned with the next line.

[MaskRay]

lld/test/COFF/pdb-thinlto.ll

5

Will .bc be slightly better for the bitcode extension name? .bc makes it clear it is not a regular object file.

[asmith]

In D78221#1985170, @MaskRay wrote:

Use the unique filenames that are used when /lldsavetemps is passed.

Is this for debug convenience? (llvm-pdbutil dump output) Or required by some tools?

MSVC expects a unique name for each module in a pdb.

[rnk]

• upload changes

[MaskRay]

Looks great!

MSVC expects a unique name for each module in a pdb.

Maybe worth mentioning this for the justification.

[rnk]

Apparently I didn't hit send...

lld/COFF/LTO.cpp

210

This is meant to preserve existing behavior from the original split loops. In the case where neither buf nor files contains an object, no input file was added. I assume that this can happen if there was an error during code generation.

---

Also, it occurs to me that split loops from before were reordering the native object files for the final link, which seems like asking non-determinism: if the object is found in the cache, it gets added later. This could be a serious cache bug fix...

lld/test/COFF/pdb-thinlto.ll

32

Speaking of oddities in the dump output, I wish it wouldn't print trailing spaces. =P

34

I think the extra spaces in the real output are a bug, I would prefer to see the output as I have it here.