On 24/02/13 20:40, Gabor Greif wrote:
Hi all,
from what I gathered so far no emission of write barriers is needed when
- running on a uniprocessor (-threaded or not)
- running on a multiprocessor sans having linked with -threaded.
Below patch suppresses the emission of 'lwsync' when no '-threaded' is
specified on PPC only. So it does not cover both criteria above.
It helps me a lot since I have a uniprocessor target that does not
understand the 'lwsync' instruction (instruction is newer than core).
Still, I have some doubts:
o do we want to extend this approach to other archs?
o possibly suppress the emission of MO_WriteBarrier in
compiler/codeGen/StgCmmBind.hs
(more care is needed to also cover compiler/cmm/CmmParse.y).
Anyway this should be a safe first step, and I'd like to push it. When
we find a general solution be can back this commit out.
What do you think?
I don't think this is the right way to do it. The -threaded flag is not
supposed to affect code generation, it only changes the RTS that gets
linked in. That is, you can compile all your code without -threaded and
then just add -threaded at the link step, and it will work.
Instead, use conditional compilation in the RTS so that the
write_barrer() calls are only present when THREADED_RTS is on.
Cheers,
Simon
Cheers,
Gabor
$ git show c0d682fb98f32e4ce5d27ff3a30f43b6cd70733e
commit c0d682fb98f32e4ce5d27ff3a30f43b6cd70733e
Author: Gabor Greif <[email protected]>
Date: Fri Feb 22 18:47:00 2013 +0100
Do not emit barriers on PPC unless we go the threaded way
diff --git a/compiler/nativeGen/PPC/CodeGen.hs
b/compiler/nativeGen/PPC/CodeGen.hs
index 92eff36..6c33cca 100644
--- a/compiler/nativeGen/PPC/CodeGen.hs
+++ b/compiler/nativeGen/PPC/CodeGen.hs
@@ -1,9 +1,8 @@
-
-----------------------------------------------------------------------------
--
-- Generating machine code (instruction selection)
--
--- (c) The University of Glasgow 1996-2004
+-- (c) The University of Glasgow 1996-2013
--
-----------------------------------------------------------------------------
@@ -906,8 +905,10 @@ genCCall'
-}
-genCCall' _ _ (PrimTarget MO_WriteBarrier) _ _
- = return $ unitOL LWSYNC
+genCCall' dflags _ (PrimTarget MO_WriteBarrier) _ _
+ = return (if WayThreaded `elem` ways dflags
+ then unitOL LWSYNC
+ else nilOL)
genCCall' _ _ (PrimTarget MO_Touch) _ _
= return $ nilOL
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