[Bug rtl-optimization/59429] New: Missed optimization opportunity in qsort-style comparison functions

[jengelh at inai dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59429

            Bug ID: 59429
           Summary: Missed optimization opportunity in qsort-style
                    comparison functions
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jengelh at inai dot de

The following code:

extern int comLG(int, int);
extern int comLE(int, int);
extern int comEL(int, int);
extern int comEG(int, int);
extern int comGL(int, int);
extern int comGE(int, int);
int comLG(int a, int b) { return (a < b) ? -1 : (a > b) ? 1 : 0; }
int comLE(int a, int b) { return (a < b) ? -1 : (a == b) ? 0 : 1; }
int comEL(int a, int b) { return (a == b) ? 0 : (a < b) ? -1 : 1; }
int comEG(int a, int b) { return (a == b) ? 0 : (a > b) ? 1 : -1; }
int comGL(int a, int b) { return (a > b) ? 1 : (a < b) ? -1 : 0; }
int comGE(int a, int b) { return (a > b) ? 1 : (a == b) ? 0 : -1; }

when compiled with:

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib64/gcc/x86_64-suse-linux/4.8/lto-wrapper
Target: x86_64-suse-linux
Configured with: ../configure --prefix=/usr --infodir=/usr/share/info
--mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64
--enable-languages=c,c++,objc,fortran,obj-c++,java,ada
--enable-checking=release --with-gxx-include-dir=/usr/include/c++/4.8
--enable-ssp --disable-libssp --disable-plugin
--with-bugurl=http://bugs.opensuse.org/ --with-pkgversion='SUSE Linux'
--disable-libgcj --disable-libmudflap --with-slibdir=/lib64 --with-system-zlib
--enable-__cxa_atexit --enable-libstdcxx-allocator=new --disable-libstdcxx-pch
--enable-version-specific-runtime-libs --enable-linker-build-id
--program-suffix=-4.8 --enable-linux-futex --without-system-libunwind
--with-arch-32=i586 --with-tune=generic --build=x86_64-suse-linux
Thread model: posix
gcc version 4.8.1 20130909 [gcc-4_8-branch revision 202388] (SUSE Linux) 

yields object code with different realizations and sizes.
What I observe:

$ gcc -Os -c cmp.c
(also shows with -O3)

$ readelf -s cmp.o
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     8: 0000000000000000    16 FUNC    GLOBAL DEFAULT    1 comLG
     9: 0000000000000010    16 FUNC    GLOBAL DEFAULT    1 comLE
    10: 0000000000000020    18 FUNC    GLOBAL DEFAULT    1 comEL
    11: 0000000000000032    18 FUNC    GLOBAL DEFAULT    1 comEG
    12: 0000000000000044    18 FUNC    GLOBAL DEFAULT    1 comGL
    13: 0000000000000056    18 FUNC    GLOBAL DEFAULT    1 comGE

$ objdump -d cmp.o -Mintel
0000000000000000 <comLG>:
   0:   31 d2                   xor    edx,edx
   2:   39 f7                   cmp    edi,esi
   4:   b8 ff ff ff ff          mov    eax,0xffffffff
   9:   0f 9f c2                setg   dl
   c:   0f 4d c2                cmovge eax,edx
   f:   c3                      ret    

0000000000000010 <comLE>:
  10:   31 d2                   xor    edx,edx
  12:   39 f7                   cmp    edi,esi
  14:   b8 ff ff ff ff          mov    eax,0xffffffff
  19:   0f 95 c2                setne  dl
  1c:   0f 4d c2                cmovge eax,edx
  1f:   c3                      ret    

0000000000000020 <comEL>:
  20:   39 f7                   cmp    edi,esi
  22:   74 0b                   je     2f <comEL+0xf>
  24:   0f 9d c0                setge  al
  27:   0f b6 c0                movzx  eax,al
  2a:   8d 44 00 ff             lea    eax,[rax+rax*1-0x1]
  2e:   c3                      ret    
  2f:   31 c0                   xor    eax,eax
  31:   c3                      ret    

0000000000000032 <comEG>:
  32:   39 f7                   cmp    edi,esi
  34:   74 0b                   je     41 <comEG+0xf>
  36:   0f 9f c0                setg   al
  39:   0f b6 c0                movzx  eax,al
  3c:   8d 44 00 ff             lea    eax,[rax+rax*1-0x1]
  40:   c3                      ret    
  41:   31 c0                   xor    eax,eax
  43:   c3                      ret    

0000000000000044 <comGL>:
  44:   39 f7                   cmp    edi,esi
  46:   b8 01 00 00 00          mov    eax,0x1
  4b:   7f 08                   jg     55 <comGL+0x11>
  4d:   0f 9c c0                setl   al
  50:   0f b6 c0                movzx  eax,al
  53:   f7 d8                   neg    eax
  55:   c3                      ret    

0000000000000056 <comGE>:
  56:   39 f7                   cmp    edi,esi
  58:   b8 01 00 00 00          mov    eax,0x1
  5d:   7f 08                   jg     67 <comGE+0x11>
  5f:   0f 95 c0                setne  al
  62:   0f b6 c0                movzx  eax,al
  65:   f7 d8                   neg    eax
  67:   c3                      ret    

What I expected instead:

All functions to have the same asm.