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digitalmars.D.bugs - [Issue 4298] New: Constant array translated to unnecessary array literal creation

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4298

           Summary: Constant array translated to unnecessary array literal
                    creation
           Product: D
           Version: 2.041
          Platform: x86
        OS/Version: All
            Status: NEW
          Keywords: performance
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: rsinfu gmail.com


--- Comment #0 from Shin Fujishiro <rsinfu gmail.com> 2010-06-08 17:57:52 PDT
---
Using constant (const or immutable) dynamic array causes unnecessary
array literal creation if the constant array has an initializer.

This behavior degrades performance, and also causes the bug 4297.

Test code and the disassembled output:
--------------------
immutable int[] TABLE = [ 1, 2, 3 ];
void foo()
{
    const(int)[] tab = TABLE;
}
--------------------
_D4test3fooFZv:
        push    EBP
        mov    EBP,ESP
        push    EBX
        push    3
        push    2
        push    1
        push    3
        mov    EAX,offset FLAT:_D12TypeInfo_Axi6__initZ SYM32
        push    EAX
        call      _d_arrayliteralT PC32
        mov    ECX,EAX
        mov    EBX,3
        add    ESP,014h
        pop    EBX
        pop    EBP
        ret
--------------------

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next sibling parent d-bugmail puremagic.com writes:
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Shin Fujishiro <rsinfu gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


--- Comment #1 from Shin Fujishiro <rsinfu gmail.com> 2010-06-08 18:02:25 PDT
---
Patch against DMD r526:
====================
--- src/optimize.c
+++ src/optimize.c
   -58,10 +58,9    Expression *expandVar(int result, VarDeclaration *v)
             return e;
         }

-        Type *tb = v->type->toBasetype();
         if (result & WANTinterpret ||
             v->storage_class & STCmanifest ||
-            (tb->ty != Tsarray && tb->ty != Tstruct)
+            v->type->isscalar()
            )
         {
             if (v->init)
====================

The if condition is changed so that only scalar constants are expanded. 
Affected types are Tarray, Taarray, Tclass and Tdelegate.  Arrays and
associative arrays should not be expanded (the reported problem); classes and
delegates are not necessary to be expanded.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Shin Fujishiro <rsinfu gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|patch                       |


--- Comment #2 from Shin Fujishiro <rsinfu gmail.com> 2010-06-15 15:15:15 PDT
---
(In reply to comment #1)

With the patch in comment #1, this example does not link:
--------------------
void main()
{
    immutable s = "abc";
    auto t = s[0 .. $ - 1];
}
--------------------
% dmd -run test
test.o(.text._Dmain+0x1a): In function `_Dmain':
: undefined reference to `_D4test4mainFZv8__dollarxk'
--------------------

The link error does not occur if the dollar $ is replaced with s.length.

The real cause of the link error may be elsewhere (only $ causes a link
error?), but the patch itself doesn't work anyway.  So I remove the 'patch'
keyword.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Shin Fujishiro <rsinfu gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
         Depends on|                            |3779


--- Comment #3 from Shin Fujishiro <rsinfu gmail.com> 2010-06-15 16:26:14 PDT
---
(In reply to comment #2)
 The link error does not occur if the dollar $ is replaced with s.length.
 
 The real cause of the link error may be elsewhere (only $ causes a link
 error?), but the patch itself doesn't work anyway.  So I remove the 'patch'
 keyword.
The linker error about __dollar is caused by bug 3779. I think the patch in comment #1 is valid if that bug is fixed. Restored the patch keyword and added a dependency to bug 3779. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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prev sibling next sibling parent d-bugmail puremagic.com writes:
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David Simcha <dsimcha yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dsimcha yahoo.com


--- Comment #4 from David Simcha <dsimcha yahoo.com> 2010-07-25 10:09:58 PDT ---
*** Issue 3370 has been marked as a duplicate of this issue. ***

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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David Simcha <dsimcha yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |r.sagitario gmx.de


--- Comment #5 from David Simcha <dsimcha yahoo.com> 2010-09-08 20:11:40 PDT ---
*** Issue 4631 has been marked as a duplicate of this issue. ***

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prev sibling parent d-bugmail puremagic.com writes:
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yebblies <yebblies gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |yebblies gmail.com
         Resolution|                            |DUPLICATE


--- Comment #6 from yebblies <yebblies gmail.com> 2012-02-02 14:27:49 EST ---
*** This issue has been marked as a duplicate of issue 2356 ***

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Feb 01 2012