[GHC] #13491: UNIQUE_BITS is not crosscompiler-friendly

[GHC]

#13491: UNIQUE_BITS is not crosscompiler-friendly
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        Reporter:  slyfox            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3397
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"01b062ec3fa138b92124ce7ca4deca0ddcb474ea/ghc"
 01b062ec/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="01b062ec3fa138b92124ce7ca4deca0ddcb474ea"
 unique: fix UNIQUE_BITS crosscompilation (Trac #13491)

 The #13491 manifests best when we try to crosscompile
 from 32-bit (i386-linux) to 64-bit (powerpc64-linux)
 system:
     ./configure --target=powerpc64-unknown-linux-gnu

 The build fails at assembly time:
   "inplace/bin/ghc-stage1" ...  -c rts/StgStartup.cmm
     /tmp/ghc19687_0/ghc_4.s: Assembler messages:

     /tmp/ghc19687_0/ghc_4.s:11:0: error:
          Error: unknown pseudo-op: `.l'
        |
     11 | .L<\x00>4:
        | ^

 That happens because UNIQUE_BITS is defined in terms
 of WORD_SIZE_IN_BITS macro:
     #define UNIQUE_BITS (WORD_SIZE_IN_BITS - 8)

 WORD_SIZE_IN_BITS is 64 bits (equals to target value)
 while ghc-stage1 is still running on i386-linux

 The fix is to stop relying on target macros and use
 host's 'sizeof (HsInt)' and 'finiteBitSize' way to
 determine unique layout.

 Signed-off-by: Sergei Trofimovich <slyfox at gentoo.org>

 Test Plan: build i386-to-powerpc64 crosscompiler

 Reviewers: rwbarton, austin, bgamari

 Reviewed By: bgamari

 Subscribers: RyanGlScott, thomie

 Differential Revision: https://phabricator.haskell.org/D3397
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13491#comment:2>
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