#7307: Share top-level code for strings
---------------------------------+------------------------------------------
Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.6.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
---------------------------------+------------------------------------------
A string constant in GHC turns into
{{{
foo :: String
foo = unpackCString# "the-string'
}}}
This is a top-level thunk, and it expands into rather a lot of code like
this
{{{
.text
.align 4,0x90
.long 0
.long 22
.globl _Foo_zdfTypeableTzuds1_info
_Foo_zdfTypeableTzuds1_info:
.LcvI:
movl %esi,%eax
leal -12(%ebp),%ecx
cmpl 84(%ebx),%ecx
jb .LcvQ
addl $8,%edi
cmpl 92(%ebx),%edi
ja .LcvS
movl $_stg_CAF_BLACKHOLE_info,-4(%edi)
movl 100(%ebx),%ecx
movl %ecx,0(%edi)
leal -4(%edi),%ecx
pushl %ecx
pushl %eax
pushl %ebx
movl %eax,76(%esp)
call _newCAF
addl $12,%esp
testl %eax,%eax
je .LcvL
movl $_stg_bh_upd_frame_info,-8(%ebp)
leal -4(%edi),%eax
movl %eax,-4(%ebp)
movl $_cvJ_str,-12(%ebp)
addl $-12,%ebp
jmp _ghczmprim_GHCziCString_unpackCStringzh_info
.LcvL:
movl 64(%esp),%eax
jmp *(%eax)
.LcvS:
movl $8,116(%ebx)
.LcvQ:
movl %eax,%esi
jmp *-12(%ebx)
}}}
That's rather a lot of goop for one thunk! Of course we can share this,
by making a 2-word thunk like this:
{{{
------------------------------
| TopUnpack_info | -------|-----> "the-string"#
------------------------------
}}}
where `TopUnpack_info` is a shared RTS info-table and code that embodies
the code fragment above.
This would save useless code bloat for every constant string. (This came
up when looking at the code generated by `deriving(Typeable)`.)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7307>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
Glasgow-haskell-bugs@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
