#7498: panic : Register allocator: out of stack slots (need 147)
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Reporter: erikd | Owner:
Type: bug | Status: new
Priority: high | Milestone: 7.8.1
Component: Compiler | Version: 7.7
Resolution: | Keywords:
Os: Unknown/Multiple | Architecture: powerpc
Failure: Building GHC failed | Difficulty: Unknown
Testcase: | Blockedby:
Blocking: | Related:
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Changes (by PHO):
* owner: erikd =>
* resolution: fixed =>
* status: closed => new
* os: Linux => Unknown/Multiple
Comment:
In HEAD the stage-2 compiler segfaults at `StgReturn` because of the stack
pointer `r1` pointing to an invalid address during the compilation of
`libraries/old-time/dist-install/build/System/Time.p_o`. I found
`PPC.Instr.insertBeforeNonlocalTransfers` (possibly mistakenly) inserts
`dealloc` before every jumpish instruction including local jumps so I
modified it as follows, but my fix didn't work:
{{{
insertBeforeNonlocalTransfers :: Instr -> [Instr] -> [Instr]
insertBeforeNonlocalTransfers insert insns
= foldr p [] insns
where
-- BCTR might or might not be a non-local jump. For
-- "labeled-goto" we use JMP, and for "computed-goto" we use
-- MTCTR followed by BCTR. See 'PPC.CodeGen.genJump'.
p insn r = case insn of
JMP _ -> insert : insn : r
BCTR [] Nothing -> insert : insn : r
_ -> insn : r
-- BL and BCTRL are call-like instructions rather than jumps,
-- and are used only for C calls.
}}}
The real cause is not in the PPC specific code, but in the current
algorithm (shared with X86) for `allocMoreStack` collapsing at local
branches or fall-through to join points. Suppose we have two blocks `L0`
and `L1`, where `L0` is the proc entry point and `L1` is a join point:
{{{
L0:
...
if (...) { call something() returning to L1; }
L1:
...
return;
}}}
`allocMoreStack` modifies the code as follows, which leaves the stack
pointer at a wrong position when the condition does not hold:
{{{
L0:
move_sp_down;
...
if (...) { move_sp_up; call something() returning to L1; }
L1:
move_sp_down;
...
move_sp_up;
return;
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7498#comment:6>
GHC <http://www.haskell.org/ghc/>
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