[Bug ld/21677] New: ld 2.27 has unexplained 10x performance improvement in some cases

[mail at nh2 dot me]

https://sourceware.org/bugzilla/show_bug.cgi?id=21677

            Bug ID: 21677
           Summary: ld 2.27 has unexplained 10x performance improvement in
                    some cases
           Product: binutils
           Version: 2.26
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: mail at nh2 dot me
  Target Milestone: ---

Hi,

the GHC Haskell compiler uses ld to link its binaries.

There is currently a performance regression in GHC 8.2 that makes linking with
ld 40x slower than it was in GHC 8.0.

But we found that ld 2.27 made this regression 10x less bad than ld 2.26:

https://ghc.haskell.org/trac/ghc/ticket/13739#comment:21
https://ghc.haskell.org/trac/ghc/attachment/ticket/13739/T13739-check-ld-output

My question:

Are you aware of any performance improvement in the 2.27 release that would
explain the 10x speedup?

I read through
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob_plain;f=ld/NEWS;hb=refs/tags/binutils-2_27
but couldn't find any.

While it's great that ld 2.27 got faster, we would really like to know what
made it faster.

That might help us figure out our bug, and other users of ld would probably
also benefit from knowing about it.

Thanks!

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