[llvm-bugs] [Bug 37933] New: lld creates redundant debug entries for enums

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37933

            Bug ID: 37933
           Summary: lld creates redundant debug entries for enums
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: brucedawson at chromium.org
                CC: llvm-bugs at lists.llvm.org

While running Chrome's ShowGlobals.exe on Chrome's canary PDBs I noticed
hundreds of reports of redundant global variables that were in fact enums.

https://cs.chromium.org/chromium/src/tools/win/ShowGlobals/ShowGlobals.cc?q=showglobals.cc&sq=package:chromium&g=0&l=1

The tool has since been fixed to avoid these reports:

https://chromium-review.googlesource.com/c/chromium/src/+/1114291

However, the issue remains that redundant enum symbols are being emitted by
lld. I created a more minimal repro that is fairly convenient for anyone with
access to the Chrome source code. Using the pre-fix version of ShowGlobals.exe:

> gn gen out\default
Done. Made 8629 targets from 1585 files in 3328ms
> ninja -C out\default base && showglobals_old.exe out\default\base.dll.pdb | head
ninja: Entering directory `out\default'
[1 processes, 354/354 @ 15.1/s : 23.374s ] LINK(DLL) base.dll base.dll.lib
base.dll.pdb
#Dups   DupSize   Size  Section Symbol name     PDB name
92      736          0  0       num_bound_args  out\default\base.dll.pdb
17      136          0  0       atomic_histogram_pointer       
out\default\base.dll.pdb
30      120          0  0       TP_CALLBACK_PRIORITY_INVALID   
out\default\base.dll.pdb
30      120          0  0       PowerUserMaximum       
out\default\base.dll.pdb
30      120          0  0       JOB_OBJECT_NET_RATE_CONTROL_VALID_FLAGS
out\default\base.dll.pdb
30      120          0  0       JOB_OBJECT_NET_RATE_CONTROL_MAX_BANDWIDTH      
out\default\base.dll.pdb
30      120          0  0       JOB_OBJECT_NET_RATE_CONTROL_ENABLE     
out\default\base.dll.pdb
30      120          0  0       JOB_OBJECT_NET_RATE_CONTROL_DSCP_TAG   
out\default\base.dll.pdb
30      120          0  0       JOB_OBJECT_IO_RATE_CONTROL_STANDALONE_VOLUME   
out\default\base.dll.pdb

However if I change from the default settings (empty args.gn) to having a
single line which is "use_lld=false" then I get the following results:

#Dups   DupSize   Size  Section Symbol name     PDB name
92      736          0  0       num_bound_args  out\default\base.dll.pdb
17      136          0  0       atomic_histogram_pointer       
out\default\base.dll.pdb
11      88           0  0       instance_       out\default\base.dll.pdb
85      85           0  0       is_weak_call    out\default\base.dll.pdb
85      85           0  0       is_method       out\default\base.dll.pdb
1       64           0  0       kEnvironmentParams     
out\default\base.dll.pdb
4       64           0  0       kCookieValue    out\default\base.dll.pdb
7       56           0  0       kCircularBufferInitialCapacity 
out\default\base.dll.pdb
1       56           0  0       buffer_ out\default\base.dll.pdb

This clearly indicates that lld is creating redundant enum entries in the debug
information. These are not necessarily a problem (the new version of
ShowGlobals.exe filters out all enums) but it seemed worth reporting.

I'm not sure if this is related to the (old, fixed) bug at
https://bugs.llvm.org/show_bug.cgi?id=14108

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