[PATCH] Fix broken -fPIC on Darwin/PPC

PIC.initializePicBase_ppc was wrongly assuming that only the first block was an entry point, which resulted in the following panic when we were compiling libraries/ghc-prim/dist-install/build/GHC/Classes.dyn_o:

ghc-stage1: panic! (the 'impossible' happened)
  (GHC version 7.7.20121119 for powerpc-apple-darwin):
    allocateRegsAndSpill: Cannot read from uninitialized register
    %vI_nawI

Here is the result of -ddump-opt-cmm for the code block in question:

==================== Optimised Cmm ====================
section "data" {
    ghc-prim:GHC.Classes.$dm<={v rbx}_closure:
        const ghc-prim:GHC.Classes.$dm<={v rbx}_info;
}

==================== Optimised Cmm ====================
ghc-prim:GHC.Classes.$dm<={v rbx}_entry() //  [R4, R3, R2]
        { [(cawk,
            ghc-prim:GHC.Classes.$dm<={v rbx}_info:
                const 1310723;
                const 0;
                const 983040;),
           (cawl,
            block{v cawl}_info:
                const 0;
                const 2097152;)]
        }
    {offset
      cawk:
          /***** FETCHPC is rightly inserted here. *****/
          _s7Ce::P32 = R4;
          _s7Cd::P32 = R3;
          _s7Cc::P32 = R2;
          if ((Sp + -16) < SpLim) goto cawA; else goto cawz;
      cawA:
          R4 = _s7Ce::P32;
          R3 = _s7Cd::P32;
          R2 = _s7Cc::P32;
          R1 = I32[PicBaseReg + Lghc-prim:GHC.Classes.$dm<={v rbx}_closure$non_lazy_ptr-1b];
          call (I32[BaseReg - 4])(R4, R3, R2, R1) args: 4, res: 0, upd: 4;
      cawz:
          I32[Sp - 4] = PicBaseReg + block{v cawl}_info-1b;
          R2 = _s7Cc::P32;
          I32[Sp - 16] = I32[PicBaseReg + Lstg_ap_pp_info$non_lazy_ptr-1b];
          P32[Sp - 12] = _s7Cd::P32;
          P32[Sp - 8] = _s7Ce::P32;
          Sp = Sp - 16;
          call ghc-prim:GHC.Classes.compare{v r5v}_info(R2) returns to cawl, args: 16, res: 4, upd: 4;
      cawl:
          /***** But not here! This is the cause of panic! *****/
          if (R1 & 3 != 3) goto cawt; else goto cawn;
      cawt:
          R1 = I32[PicBaseReg + Lghc-prim:GHC.Types.True{(w) d 6u}_closure$non_lazy_ptr-1b] + 2;
          Sp = Sp + 4;
          call (P32[Sp])(R1) args: 4, res: 0, upd: 4;
      cawn:
          R1 = I32[PicBaseReg + Lghc-prim:GHC.Types.False{(w) d 68}_closure$non_lazy_ptr-1b] + 1;
          Sp = Sp + 4;
          call (P32[Sp])(R1) args: 4, res: 0, upd: 4;
    }
}

To pull my patch:

% git fetch git://github.com/phonohawk/ghc.git darwin-ppc-pic-fix

I'm pretty sure that Linux/ppc32 suffers from the same bug too, but I have no idea how to fix its awfully complicated logic so I have no choice but to leave it untouched.

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture