Re: Strictness in data declaration not matched in assembler?

True, if there can be indirections then that's bad news. That would make strict fields much less efficient. But I don't see why indirections should be needed. Simon? On Wed, Oct 15, 2008 at 4:21 PM, Jan-Willem Maessen wrote:

On Oct 15, 2008, at 11:08 AM, Lennart Augustsson wrote:

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I totally agree. Getting the value of the field should just evaluate x and then use a pointer indirection; there should be no conditional jumps involved in getting the value. GHC is just doing the wrong thing.

Can indirection nodes occur in this context? [I'd think not, but it depends on what pointer we're storing when we force the thunk in the constructor.] I could see the need for the test if indirection handling is required.

-Jan

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-- Lennart

On Wed, Oct 15, 2008 at 3:58 PM, Tyson Whitehead wrote:

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On Wednesday 15 October 2008 10:48:26 you wrote:

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Strictness does not imply unboxing.

To see why not, think about the fact that unboxing breaks sharing. By keeping the pointer-indirection in place, we can share even strict fields between related values.

I believe I realize that. What I was wondering about was the fact that it seemed to think the pointer might be to a thunk (instead of constructor closure). Doesn't the strictness flag mean the following assembler would work

sni_info: movq 7(%rbx),%rbx movq $snj_info,(%rbp) jmp snj_info

(which could be cleaned up further by combining it with snj_info) instead of

sni_info: movq 7(%rbx),%rbx movq $snj_info,(%rbp) testq $7,%rbx jne snj_info jmp *(%rbx)

(i.e., the whole test if it is a thunk and conditionally evaluate it bit is unnecessary due to constructor the strictness flag).

Cheers! -Tyson _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users

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