[GHC] #16084: Improve link times on Windows

[GHC]

#16084: Improve link times on Windows
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  upstream
        Priority:  high              |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Windows           |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by awson):

 Replying to [ticket:16084 bgamari]:
 > One option to fix this is to try using LLD for linking. Unfortunately
 the msys2 `gcc` does not support `-fuse-ld=lld`.

 LLD won't magically help here. Latest improvements by Martin Storsjö
 (mstorsjo) have made LLD able to link some mingw **gcc**-generated code,
 but, alas, when assembling **GHC**-generated assembly, mingw **gas**
 produces (I believe this is a sort of "optimisation") non-standard
 relocations, which LLD is unable to deal with (honestly, I haven't checked
 if this is still the case, but it was definitely so a year or two ago).

 For quite a bit of time I have a GHC port which works flawlessly against
 native Windows SDK and uses clang in MSVC mode and MS or LLD linker. After
 recent LLD improvements by mstorsjo I've decided to try a less intrusive
 approach — use clang in mingw mode and LLD linker. That required quite a
 bit of work and I finally managed to produce stage2 GHC executable, which
 appeared to be severely broken — it is unable to do anything.

 TL;DR the current state of affairs is that `lld` **can't** serve as a
 drop-in replacement for `ld` not only when GNU binutils toolchain is used,
 but even when `clang` is used as an assembler.

 Perhaps, the latter might work against mingw SDK built using LLVM tools
 (e.g. https://github.com/mstorsjo/llvm-mingw), but I never tried this.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16084#comment:5>
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