[GHC] #4213: LLVM: Add support for TNTC to LLVM compiler suite

[GHC]

#4213: LLVM: Add support for TNTC to LLVM compiler suite
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        Reporter:  dterei            |            Owner:  dterei
            Type:  feature request   |           Status:  new
        Priority:  low               |        Milestone:  7.6.2
       Component:  Compiler (LLVM)   |          Version:  6.13
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by rwbarton):

 If we mangle the symbol table of the output .o file then it will be too
 late for intra-module references to be fixed up. So either we need to
 mangle the assembly anyways, or we need to adjust the input to LLVM taking
 this into account. That means when we build a thunk, we need to obtain the
 pointer to the end of the info table, which will be the symbol as known by
 LLVM plus some constant, but only when the symbol is in the current
 module; and when we want to jump to another function we need that function
 to start with one of these little jmps to skip the info table, since we
 can't tell LLVM to do a jump to a symbol plus some random byte offset.

 The symbol offset approach sounds workable to me.

 I assume it's not possible to tell LLVM to emit a global symbol in the
 middle of a function, as a second entry point? That would also solve our
 problem, as we could then stick the _info symbol after the prefix data and
 use it (rather than the symbol for the function, which points to the start
 of the info table) for building thunks and calling as usual.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4213#comment:17>
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