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digitalmars.D.bugs - [Issue 10323] New: getAMDcacheinfo needlessly allocates

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=10323

           Summary: getAMDcacheinfo needlessly allocates
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: minor
          Priority: P2
         Component: druntime
        AssignedTo: nobody puremagic.com
        ReportedBy: destructionator gmail.com


--- Comment #0 from Adam D. Ruppe <destructionator gmail.com> 2013-06-10
11:55:55 PDT ---
src/druntime/src/core/cpuid.d line 544:

        immutable ubyte [] assocmap = [ 0, 1, 2, 0, 4, 0, 8, 0, 16, 0, 32, 48,
64, 96, 128, 0xFF ];


The real problem here is that a array initializer allocates, even if all the
data is static, and the compiler should probably be fixed, but in the mean time
I think we should go ahead and kill as many allocations as possible from
druntime, and this is one of them.

In my experimentation, I found just sticking "static" in front of this line
solved the immediate problem.

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next sibling parent d-bugmail puremagic.com writes:
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hsteoh quickfur.ath.cx changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hsteoh quickfur.ath.cx


--- Comment #1 from hsteoh quickfur.ath.cx 2013-06-10 13:04:39 PDT ---
Yeah, for array initializers to *always* allocate seems wrong to me. Is there a
bug for it?

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--- Comment #2 from Adam D. Ruppe <destructionator gmail.com> 2013-06-10
13:21:06 PDT ---
Well, they don't *always* allocate - in the variable is static, they don't. But
if not they do and that sucks. I'm pretty sure it is a well known issue and
this bug seems close: http://d.puremagic.com/issues/show_bug.cgi?id=6421 but is
talking about static so not sure.

Bugzilla search never works easily for me :(

My preferred solution to the array literal question is if the contents are all
literal values too (or, ideally, if they can evaluate to literals with CTFE),
put the literal into static data like you would with a string literal. Well,
maybe not like a string literal, since they are read only and arrays expect to
be writable. Maybe put them in the initialized data segment instead, with
read/write.

Then only do a runtime allocation if the literal isn't all literals, e.g. "int
x = 10; auto b = [x, 100];", b would be an ok allocation because x is a runtime
value.


Nevertheless, in druntime we should be mindful of it and at least mark these
arrays static so they work today, pending an answer to the bigger question.

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--- Comment #3 from Adam D. Ruppe <destructionator gmail.com> 2013-06-10
13:27:25 PDT ---
thinking some more about that data segment thing, maybe that won't work either
because ~= would try to find gc info, to check capacity, that doesn't exist
there. But I'm sure that can be worked around, the literal could perhaps write
out a dummy gc info block before the array informing append that it has zero
extra capacity.

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--- Comment #4 from Steven Schveighoffer <schveiguy yahoo.com> 2013-06-10
13:32:46 PDT ---
(In reply to comment #3)
 thinking some more about that data segment thing, maybe that won't work either
 because ~= would try to find gc info, to check capacity, that doesn't exist
 there. But I'm sure that can be worked around, the literal could perhaps write
 out a dummy gc info block before the array informing append that it has zero
 extra capacity.
The runtime can detect when it's not dealing with non-GC memory (think about appending to stack data). Appending would simply allocate a new GC block. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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David Nadlinger <code klickverbot.at> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |code klickverbot.at


--- Comment #5 from David Nadlinger <code klickverbot.at> 2013-06-10 14:23:17
PDT ---
It should be possible to treat immutable arrays just like static immutable
ones.

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--- Comment #6 from Adam D. Ruppe <destructionator gmail.com> 2013-10-04
18:59:13 PDT ---
pull # 625 fixed

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prev sibling parent d-bugmail puremagic.com writes:
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Adam D. Ruppe <destructionator gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


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