[Bug middle-end/21478] New: Improve initialization of sparse local arrays

[Bug middle-end/21478] New: Improve initialization of sparse local arrays

[jconner at apple dot com]

Large local arrays that are initialized to constant values, gcc uses a static template and a call to 
memcpy.  If these arrays are all or mostly zeroes, if we clear the array using memset and then initialize 
the non-zero values inline, it is generally better in two ways:
a) it is faster
b) it requires less program memory overhead to store the array of initializers

Here is an example of source code that gcc could do better on:

    void bar (char *);
    void foo (void)
    {
      char bigarray[0x1000] = { 0 };

      bar (&bigarray[0]);
    }

Which generates a 0x1000 byte constant array of zeroes.  Instead, it would be nice if gcc would just 
memset the region to zeroes.

This construct is used extensively in the FAAD2 open source AAC encoder/decoder library, resulting in 
a 35%+ increase in size.

AFAICT, this applies to all targets, not just ARM.

-- 
           Summary: Improve initialization of sparse local arrays
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jconner at apple dot com
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: powerpc-apple-darwin7.9.0
GCC target triplet: arm-none-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21478

[Bug middle-end/21478] Improve initialization of sparse local arrays

[jconner at apple dot com]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21478

[Bug middle-end/21478] Improve initialization of sparse local arrays

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-09 22:30 -------
Confirmed, if you did "      char bigarray[0x1000] = {  };" instead it does the correct thing but doing {} is 
GNU extension.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   GCC host triplet|powerpc-apple-darwin7.9.0   |
 GCC target triplet|arm-none-elf                |
   Last reconfirmed|0000-00-00 00:00:00         |2005-05-09 22:30:30
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21478

[Bug middle-end/21478] Improve initialization of sparse local arrays

[jconner at apple dot com]

------- Additional Comments From jconner at apple dot com  2005-05-10 00:50 -------
Proposed patch here:
http://gcc.gnu.org/ml/gcc-patches/2005-05/msg00773.html


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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21478

[Bug middle-end/21478] Improve initialization of sparse local arrays

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-17 17:24 -------
*** Bug 21626 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |etienne_lorrain at yahoo dot
                   |                            |fr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21478

[Bug middle-end/21478] Improve initialization of sparse local arrays

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-06-01 21:34 -------
Subject: Bug 21478

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	rth@gcc.gnu.org	2005-06-01 21:34:28

Modified files:
	gcc            : ChangeLog gimplify.c 

Log message:
	PR 21478
	* gimplify.c (gimplify_init_constructor): Don't spill initializer
	to read-only memory if it's sparse.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.8987&r2=2.8988
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/gimplify.c.diff?cvsroot=gcc&r1=2.130&r2=2.131



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21478

[Bug middle-end/21478] Improve initialization of sparse local arrays

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-06-02 19:17 -------
Fixed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21478