[Bug regression/44392] New: libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[Bug regression/44392] New: libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[raj dot khem at gmail dot com]

When using --enable-target-optspace on gcc 4.5 function __bswapsi2 in libgcc
generates call to itself which causes infinite recursion. Here is disassembly.

$ arm-none-linux-uclibcgnueabi-objdump -d _bswapsi2_s.o 

_bswapsi2_s.o:     file format elf32-littlearm


Disassembly of section .text:

00000000 <__bswapsi2>:
   0:   e92d4008        push    {r3, lr}
   4:   ebfffffe        bl      0 <__bswapsi2>
   8:   e8bd8008        pop     {r3, pc}


This does not happen on -O1, O2 or O3 where is computes the swapping
and does not call the libgcc function. With gcc 4.4 it does not call
libgcc function even at -Os. I have only tested it on arm architecture.

Here is little program which demonstrates it

typedef signed int SItype;
SItype
__bswapsi2 (SItype u)
{
  return ((((u) & 0xff000000) >> 24)
          | (((u) & 0x00ff0000) >>  8)
          | (((u) & 0x0000ff00) <<  8)
          | (((u) & 0x000000ff) << 24));
}


here is how the gcc was built

/scratch/oe/work/armv5te-oe-linux-gnueabi/gcc-cross-intermediate-4.5-r0+svnr160043/gcc-4.5/build.x86_64-linux.arm-oe-linux-gnueabi/gcc/xgcc
-v
Using built-in specs.
COLLECT_GCC=/scratch/oe/work/armv5te-oe-linux-gnueabi/gcc-cross-intermediate-4.5-r0+svnr160043/gcc-4.5/build.x86_64-linux.arm-oe-linux-gnueabi/gcc/xgcc
Target: arm-oe-linux-gnueabi
Configured with:
/scratch/oe/work/armv5te-oe-linux-gnueabi/gcc-cross-intermediate-4.5-r0+svnr160043/gcc-4.5/configure
--build=x86_64-linux --host=x86_64-linux --target=arm-oe-linux-gnueabi
--prefix=/scratch/oe/cross/armv5te --exec_prefix=/scratch/oe/cross/armv5te
--bindir=/scratch/oe/cross/armv5te/bin --sbindir=/scratch/oe/cross/armv5te/bin
--libexecdir=/scratch/oe/cross/armv5te/libexec
--datadir=/scratch/oe/cross/armv5te/share
--sysconfdir=/scratch/oe/cross/armv5te/etc
--sharedstatedir=/scratch/oe/cross/armv5te/com
--localstatedir=/scratch/oe/cross/armv5te/var
--libdir=/scratch/oe/cross/armv5te/lib
--includedir=/scratch/oe/cross/armv5te/include
--oldincludedir=/scratch/oe/cross/armv5te/include
--infodir=/scratch/oe/cross/armv5te/share/info
--mandir=/scratch/oe/cross/armv5te/share/man
--with-local-prefix=/scratch/oe/sysroots/armv5te-oe-linux-gnueabi/usr
--enable-shared --disable-multilib --disable-threads --enable-languages=c
--program-prefix=arm-oe-linux-gnueabi-
--with-sysroot=/scratch/oe/sysroots/armv5te-oe-linux-gnueabi
--with-build-sysroot=/scratch/oe/sysroots/armv5te-oe-linux-gnueabi
--enable-target-optspace --disable-libmudflap --disable-libgomp
--disable-libssp --with-float=soft --program-prefix=arm-oe-linux-gnueabi-
--enable-__cxa_atexit
Thread model: single
gcc version 4.5.1 20100530 (prerelease) (GCC)


-- 
           Summary: libgcc compile with --enable-target-optspace (-Os)
                    causes recursion in __bswapsi2
           Product: gcc
           Version: 4.5.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: regression
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: raj dot khem at gmail dot com
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: arm-oe-linux-gnueabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2010-06-02 19:14 -------
Heh.  arm does have a bswapsi pattern though - why is that expanding to a call
at -Os?


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|regression                  |target
            Summary|libgcc compile with --      |[4.5/4.6 Regression] libgcc
                   |enable-target-optspace (-Os)|compile with --enable-
                   |causes recursion in         |target-optspace (-Os) causes
                   |__bswapsi2                  |recursion in __bswapsi2
   Target Milestone|---                         |4.5.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[raj dot khem at gmail dot com]

------- Comment #2 from raj dot khem at gmail dot com  2010-06-02 22:52 -------
(In reply to comment #1)
> Heh.  arm does have a bswapsi pattern though - why is that expanding to a call
> at -Os?
> 

IIUC this pattern only triggers for armv6+ architectures. The problem I see is
on
a armv5te


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[mikpe at it dot uu dot se]

------- Comment #3 from mikpe at it dot uu dot se  2010-06-06 19:54 -------
I've looked at this, and as far as I can tell it's caused by two separate
improvements in 4.5 that are Ok individually but cause libgcc's __bswapsi2 to
call itself when combined (and certain build options are selected).

1. The middle-end now recognises C idioms for bswap and represents them as
calls to the builtin bswap.

2. The ARM backend now generates much better code for the builtin bswap, but
for archs prior to ARMv6 when -Os is enabled the .md expander arranges to have
a libcall emitted instead.

Consequently, then building for (say) ARMv5 with --enable-target-optspace:
a) the middle-end represents the C bswap idiom in libgcc2.c:__bswapsi2 () as a
call to the builtin
b) the ARM backend (not knowing it's compiling libgcc) emits a libcall
c) hence __bswapsi2 () calls itself

The only way I see around this is to add a compiler option (-fin-libgcc say),
set it when compiling libgcc routines (similar to -DIN_LIBGCC2), check for it
in the ARM bswap expander, and if set ignore -Os in the arch < v6 case.


-- 

mikpe at it dot uu dot se changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mikpe at it dot uu dot se


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2010-06-06 20:22 -------
No, the arm backend should not claim to implement bswapsi when it in fact emits
a libcall.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[ramana at gcc dot gnu dot org]

-- 

ramana at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |wrong-code
   Last reconfirmed|0000-00-00 00:00:00         |2010-06-22 00:46:00
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[ramana at gcc dot gnu dot org]

------- Comment #5 from ramana at gcc dot gnu dot org  2010-06-22 00:51 -------
Khem, 

Can you check if this fixes your problem ? Feel free to submit this to
gcc-patches@ if you get around to testing this before me. 

Ramana


diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index 628bd62..9dcceea 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -11296,7 +11296,7 @@
 (define_expand "bswapsi2"
   [(set (match_operand:SI 0 "s_register_operand" "=r")
        (bswap:SI (match_operand:SI 1 "s_register_operand" "r")))]
-"TARGET_EITHER"
+"TARGET_EITHER && (arm_arch6 || ( !arm_arch6 && !optimize_size))"
 "
   if (!arm_arch6)
     {


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[jakub at gcc dot gnu dot org]

------- Comment #6 from jakub at gcc dot gnu dot org  2010-06-22 05:50 -------
Why not just:
TARGET_EITHER && (arm_arch6 || !optimize_size)
?  That !arm_arch6 && is completely redundant there.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[raj dot khem at gmail dot com]

------- Comment #7 from raj dot khem at gmail dot com  2010-06-22 15:42 -------
(In reply to comment #6)
> Why not just:
> TARGET_EITHER && (arm_arch6 || !optimize_size)
> ?  That !arm_arch6 && is completely redundant there.
> 

Hi Ramana

the patch along with Jakub's suggestions works for me.

Thx

-Khem


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2010-06-24 21:38 -------
If nobody tests and submits this patch the issue will be not fixed for 4.5.1.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2010-07-31 09:29 -------
GCC 4.5.1 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.5.1                       |4.5.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[jakub at gcc dot gnu dot org]

------- Comment #10 from jakub at gcc dot gnu dot org  2010-08-25 16:48 -------
The patch has been approved, why hasn't been applied?
http://gcc.gnu.org/ml/gcc-patches/2010-07/msg00381.html


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ramana at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392

[Bug target/44392] [4.5/4.6 Regression] libgcc compile with --enable-target-optspace (-Os) causes recursion in __bswapsi2

[ramana at gcc dot gnu dot org]

------- Comment #11 from ramana at gcc dot gnu dot org  2010-09-08 21:36 -------
Subject: Bug 44392

Author: ramana
Date: Wed Sep  8 21:35:48 2010
New Revision: 164029

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=164029
Log:
2010-09-08  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>

        PR target/44392
        * config/arm/arm.md (bswapsi2): Handle condition correctly
        for armv6 and optimize_size.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/arm/arm.md


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44392