[Bug ld/30724] New: massive ld performance regression

[Stromeko at nexgo dot de]

https://sourceware.org/bugzilla/show_bug.cgi?id=30724

            Bug ID: 30724
           Summary: massive ld performance regression
           Product: binutils
           Version: 2.41
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: Stromeko at nexgo dot de
  Target Milestone: ---

On Cygwin there is a massive performance regression during the link phase with
version 2.41.  The degradation is superlinear in the number of objects involved
and I have observed link operations that take more than 30× longer than with
the previous version.

One of the changes suspected was 38395c77, but that doesn't seem to be the main
contributor to the regression (at least not in isolation).

* cygport protobuf-21.12 compile

2.39: 1420.820u 143.747s  3:20.37 780.8%      0+0k 0+0io 41531073pf+0w
2.40: 1429.088u 140.548s  3:18.48 790.8%      0+0k 0+0io 41615637pf+0w
2.41: 1496.555u 524.457s 10:07.31 332.7%      0+0k 0+0io 41570112pf+0w

* only the linking of protobuf-21.12

2.39:   14.212u   2.614s  0:20.54 81.8%       0+0k 0+0io 1909884pf+0w
2.40:   13.371u   0.839s  0:20.46 69.4%       0+0k 0+0io 1910885pf+0w
2.41:   85.507u 373.960s  7:55.39 96.6%       0+0k 0+0io 1905021pf+0w
38395c77/pdb.c w/o call to qsort
        84.933u 363.715s  7:37.01 98.1%       0+0k 0+0io 1906464pf+0w
38395c77/pdb.c full revert
        82.964u 361.461s  7:30.39 98.6%       0+0k 0+0io 1906266pf+0w

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