Merge adjacent stores of constants?

array.c

#include <stdio.h>
#include <limits.h>
#include <stdint.h>

static uint64_t buf[2];

#define NOINLINE __attribute__ ((noinline))

static void NOINLINE func1() {
  uint8_t* p = (uint8_t*)buf;
  p[0] = 0xFF;
  p[1] = 0xFF;
  p[2] = 0xFF;
  p[3] = 0xFF;
  p[4] = 0xFF;
  p[5] = 0xFF;
  p[6] = 0xFF;
  p[7] = 0xFF;
  p[8] = 0xFF;
  p[9] = 0xFF;
  p[10] = 0xFF;
  p[11] = 0xFF;
  p[12] = 0xFF;
  p[13] = 0xFF;
  p[14] = 0xFF;
  p[15] = 0xFF;
}

static void NOINLINE func2() {
  uint32_t* p = (uint32_t*)buf;
  p[0] = 0xFFFFFFFF;
  p[1] = 0xFFFFFFFF;
  p[2] = 0xFFFFFFFF;
  p[3] = 0xFFFFFFFF;
}

static void NOINLINE func3() {
  uint64_t* p = (uint64_t*)buf;
  p[0] = 0xFFFFFFFFFFFFFFFF;
  p[1] = 0xFFFFFFFFFFFFFFFF;
}

int main(int argc, const char *argv[]) {
  unsigned i;
  // Run one of the functions lots of times...
  for(i = 0; i < UINT_MAX; ++i) {
    FUNC();
  }

  // Misc code to just use all of buf
  unsigned v = 0;
  for (i = 0 ; i < 16; ++i)
    v |= buf[i];
  printf("%u\n", v);

  return 0;
}

run.sh

#!/bin/sh

CC=${CC-gcc}
CFLAGS="-mtune=generic -mno-sse -O3"

$CC -v 2>&1

$CC $CFLAGS array.c -o test1 -DFUNC=func1
$CC $CFLAGS array.c -o test2 -DFUNC=func2
$CC $CFLAGS array.c -o test3 -DFUNC=func3

gdb --batch -ex "disassemble /r func1" test1
gdb --batch -ex "disassemble /r func2" test2
gdb --batch -ex "disassemble /r func3" test3

echo ""
echo "=== Func1 Timing ==="
(time ./test1 > /dev/null) 2>&1
echo "=== Func2 Timing ==="
(time ./test2 > /dev/null) 2>&1
echo "=== Func3 Timing ==="
(time ./test3 > /dev/null) 2>&1

rm test1 test2 test3

test.log

Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre --enable-libgcj-multifile --enable-java-maintainer-mode --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib --with-ppl --with-cloog --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.4.6 20110731 (Red Hat 4.4.6-3) (GCC) 
Dump of assembler code for function func1:
   0x0000000000400500 <+0>:	 c6 05 39 15 00 00 ff	movb   $0xff,0x1539(%rip)        # 0x401a40 <buf>
   0x0000000000400507 <+7>:	 c6 05 33 15 00 00 ff	movb   $0xff,0x1533(%rip)        # 0x401a41 <buf+1>
   0x000000000040050e <+14>:	 c6 05 2d 15 00 00 ff	movb   $0xff,0x152d(%rip)        # 0x401a42 <buf+2>
   0x0000000000400515 <+21>:	 c6 05 27 15 00 00 ff	movb   $0xff,0x1527(%rip)        # 0x401a43 <buf+3>
   0x000000000040051c <+28>:	 c6 05 21 15 00 00 ff	movb   $0xff,0x1521(%rip)        # 0x401a44 <buf+4>
   0x0000000000400523 <+35>:	 c6 05 1b 15 00 00 ff	movb   $0xff,0x151b(%rip)        # 0x401a45 <buf+5>
   0x000000000040052a <+42>:	 c6 05 15 15 00 00 ff	movb   $0xff,0x1515(%rip)        # 0x401a46 <buf+6>
   0x0000000000400531 <+49>:	 c6 05 0f 15 00 00 ff	movb   $0xff,0x150f(%rip)        # 0x401a47 <buf+7>
   0x0000000000400538 <+56>:	 c6 05 09 15 00 00 ff	movb   $0xff,0x1509(%rip)        # 0x401a48 <buf+8>
   0x000000000040053f <+63>:	 c6 05 03 15 00 00 ff	movb   $0xff,0x1503(%rip)        # 0x401a49 <buf+9>
   0x0000000000400546 <+70>:	 c6 05 fd 14 00 00 ff	movb   $0xff,0x14fd(%rip)        # 0x401a4a <buf+10>
   0x000000000040054d <+77>:	 c6 05 f7 14 00 00 ff	movb   $0xff,0x14f7(%rip)        # 0x401a4b <buf+11>
   0x0000000000400554 <+84>:	 c6 05 f1 14 00 00 ff	movb   $0xff,0x14f1(%rip)        # 0x401a4c <buf+12>
   0x000000000040055b <+91>:	 c6 05 eb 14 00 00 ff	movb   $0xff,0x14eb(%rip)        # 0x401a4d <buf+13>
   0x0000000000400562 <+98>:	 c6 05 e5 14 00 00 ff	movb   $0xff,0x14e5(%rip)        # 0x401a4e <buf+14>
   0x0000000000400569 <+105>:	 c6 05 df 14 00 00 ff	movb   $0xff,0x14df(%rip)        # 0x401a4f <buf+15>
   0x0000000000400570 <+112>:	 c3	retq   
End of assembler dump.
Dump of assembler code for function func2:
   0x0000000000400500 <+0>:	 c7 05 e6 14 00 00 ff ff ff ff	movl   $0xffffffff,0x14e6(%rip)        # 0x4019f0 <buf>
   0x000000000040050a <+10>:	 c7 05 e0 14 00 00 ff ff ff ff	movl   $0xffffffff,0x14e0(%rip)        # 0x4019f4 <buf+4>
   0x0000000000400514 <+20>:	 c7 05 da 14 00 00 ff ff ff ff	movl   $0xffffffff,0x14da(%rip)        # 0x4019f8 <buf+8>
   0x000000000040051e <+30>:	 c7 05 d4 14 00 00 ff ff ff ff	movl   $0xffffffff,0x14d4(%rip)        # 0x4019fc <buf+12>
   0x0000000000400528 <+40>:	 c3	retq   
End of assembler dump.
Dump of assembler code for function func3:
   0x0000000000400500 <+0>:	 48 c7 c0 ff ff ff ff	mov    $0xffffffffffffffff,%rax
   0x0000000000400507 <+7>:	 48 89 05 d2 14 00 00	mov    %rax,0x14d2(%rip)        # 0x4019e0 <buf>
   0x000000000040050e <+14>:	 48 89 05 d3 14 00 00	mov    %rax,0x14d3(%rip)        # 0x4019e8 <buf+8>
   0x0000000000400515 <+21>:	 c3	retq   
End of assembler dump.

=== Func1 Timing ===

real	0m20.464s
user	0m20.434s
sys	0m0.000s
=== Func2 Timing ===

real	0m9.630s
user	0m9.615s
sys	0m0.000s
=== Func3 Timing ===

real	0m7.219s
user	0m7.203s
sys	0m0.003s

test2.log

Reading specs from /usr/lib64/gcc/x86_64-slackware-linux/4.7.1/specs
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-slackware-linux/4.7.1/lto-wrapper
Target: x86_64-slackware-linux
Configured with: ../gcc-4.7.1/configure --prefix=/usr --libdir=/usr/lib64 --mandir=/usr/man --infodir=/usr/info --enable-shared --enable-bootstrap --enable-languages=ada,c,c++,fortran,go,java,lto,objc --enable-threads=posix --enable-checking=release --enable-objc-gc --with-system-zlib --with-python-dir=/lib64/python2.7/site-packages --disable-libunwind-exceptions --enable-__cxa_atexit --enable-libssp --enable-lto --with-gnu-ld --verbose --enable-java-home --with-java-home=/usr/lib64/jvm/jre --with-jvm-root-dir=/usr/lib64/jvm --with-jvm-jar-dir=/usr/lib64/jvm/jvm-exports --with-arch-directory=amd64 --with-antlr-jar=/home/slackware/slackbuilds/gcc/antlr-runtime-3.4.jar --enable-multilib --target=x86_64-slackware-linux --build=x86_64-slackware-linux --host=x86_64-slackware-linux
Thread model: posix
gcc version 4.7.1 (GCC) 
Dump of assembler code for function func1:
   0x00000000004006a0 <+0>:	48 8b 05 09 01 00 00	mov    0x109(%rip),%rax        # 0x4007b0
   0x00000000004006a7 <+7>:	48 89 05 22 04 20 00	mov    %rax,0x200422(%rip)        # 0x600ad0 <buf>
   0x00000000004006ae <+14>:	48 89 05 23 04 20 00	mov    %rax,0x200423(%rip)        # 0x600ad8 <buf+8>
   0x00000000004006b5 <+21>:	c3	retq   
End of assembler dump.
Dump of assembler code for function func2:
   0x00000000004006a0 <+0>:	48 8b 05 09 01 00 00	mov    0x109(%rip),%rax        # 0x4007b0
   0x00000000004006a7 <+7>:	48 89 05 22 04 20 00	mov    %rax,0x200422(%rip)        # 0x600ad0 <buf>
   0x00000000004006ae <+14>:	48 89 05 23 04 20 00	mov    %rax,0x200423(%rip)        # 0x600ad8 <buf+8>
   0x00000000004006b5 <+21>:	c3	retq   
End of assembler dump.
Dump of assembler code for function func3:
   0x00000000004006a0 <+0>:	48 c7 c0 ff ff ff ff	mov    $0xffffffffffffffff,%rax
   0x00000000004006a7 <+7>:	48 89 05 22 04 20 00	mov    %rax,0x200422(%rip)        # 0x600ad0 <buf>
   0x00000000004006ae <+14>:	48 89 05 23 04 20 00	mov    %rax,0x200423(%rip)        # 0x600ad8 <buf+8>
   0x00000000004006b5 <+21>:	c3	retq   
End of assembler dump.

=== Func1 Timing ===

real	0m9.941s
user	0m9.938s
sys	0m0.000s
=== Func2 Timing ===

real	0m9.943s
user	0m9.937s
sys	0m0.001s
=== Func3 Timing ===

real	0m9.938s
user	0m9.935s
sys	0m0.000s

test3.log

clang version 3.1 (git@github.com:llvm-mirror/clang.git 6f576c9bfa9a22e2801485768fe56b3336ea18a7) (git@github.com:llvm-mirror/llvm.git 02b87df98afb03136a1f5076c042696c98524947)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Dump of assembler code for function func1:
   0x00000000004005b0 <+0>:	 c6 05 69 14 00 00 ff	movb   $0xff,0x1469(%rip)        # 0x401a20 <buf>
   0x00000000004005b7 <+7>:	 c6 05 63 14 00 00 ff	movb   $0xff,0x1463(%rip)        # 0x401a21 <buf+1>
   0x00000000004005be <+14>:	 c6 05 5d 14 00 00 ff	movb   $0xff,0x145d(%rip)        # 0x401a22 <buf+2>
   0x00000000004005c5 <+21>:	 c6 05 57 14 00 00 ff	movb   $0xff,0x1457(%rip)        # 0x401a23 <buf+3>
   0x00000000004005cc <+28>:	 c6 05 51 14 00 00 ff	movb   $0xff,0x1451(%rip)        # 0x401a24 <buf+4>
   0x00000000004005d3 <+35>:	 c6 05 4b 14 00 00 ff	movb   $0xff,0x144b(%rip)        # 0x401a25 <buf+5>
   0x00000000004005da <+42>:	 c6 05 45 14 00 00 ff	movb   $0xff,0x1445(%rip)        # 0x401a26 <buf+6>
   0x00000000004005e1 <+49>:	 c6 05 3f 14 00 00 ff	movb   $0xff,0x143f(%rip)        # 0x401a27 <buf+7>
   0x00000000004005e8 <+56>:	 c6 05 39 14 00 00 ff	movb   $0xff,0x1439(%rip)        # 0x401a28 <buf+8>
   0x00000000004005ef <+63>:	 c6 05 33 14 00 00 ff	movb   $0xff,0x1433(%rip)        # 0x401a29 <buf+9>
   0x00000000004005f6 <+70>:	 c6 05 2d 14 00 00 ff	movb   $0xff,0x142d(%rip)        # 0x401a2a <buf+10>
   0x00000000004005fd <+77>:	 c6 05 27 14 00 00 ff	movb   $0xff,0x1427(%rip)        # 0x401a2b <buf+11>
   0x0000000000400604 <+84>:	 c6 05 21 14 00 00 ff	movb   $0xff,0x1421(%rip)        # 0x401a2c <buf+12>
   0x000000000040060b <+91>:	 c6 05 1b 14 00 00 ff	movb   $0xff,0x141b(%rip)        # 0x401a2d <buf+13>
   0x0000000000400612 <+98>:	 c6 05 15 14 00 00 ff	movb   $0xff,0x1415(%rip)        # 0x401a2e <buf+14>
   0x0000000000400619 <+105>:	 c6 05 0f 14 00 00 ff	movb   $0xff,0x140f(%rip)        # 0x401a2f <buf+15>
   0x0000000000400620 <+112>:	 c3	retq   
End of assembler dump.
Dump of assembler code for function func2:
   0x00000000004005b0 <+0>:	 c7 05 16 14 00 00 ff ff ff ff	movl   $0xffffffff,0x1416(%rip)        # 0x4019d0 <buf>
   0x00000000004005ba <+10>:	 c7 05 10 14 00 00 ff ff ff ff	movl   $0xffffffff,0x1410(%rip)        # 0x4019d4 <buf+4>
   0x00000000004005c4 <+20>:	 c7 05 0a 14 00 00 ff ff ff ff	movl   $0xffffffff,0x140a(%rip)        # 0x4019d8 <buf+8>
   0x00000000004005ce <+30>:	 c7 05 04 14 00 00 ff ff ff ff	movl   $0xffffffff,0x1404(%rip)        # 0x4019dc <buf+12>
   0x00000000004005d8 <+40>:	 c3	retq   
End of assembler dump.
Dump of assembler code for function func3:
   0x00000000004005b0 <+0>:	 48 c7 05 05 14 00 00 ff ff ff ff	movq   $0xffffffffffffffff,0x1405(%rip)        # 0x4019c0 <buf>
   0x00000000004005bb <+11>:	 48 c7 05 02 14 00 00 ff ff ff ff	movq   $0xffffffffffffffff,0x1402(%rip)        # 0x4019c8 <buf+8>
   0x00000000004005c6 <+22>:	 c3	retq   
End of assembler dump.

=== Func1 Timing ===

real	0m20.456s
user	0m20.426s
sys	0m0.000s
=== Func2 Timing ===

real	0m8.420s
user	0m8.406s
sys	0m0.001s
=== Func3 Timing ===

real	0m8.411s
user	0m8.398s
sys	0m0.000s

test4.log

clang version 3.2 (http://llvm.org/git/clang.git git@github.com:dtzWill/ioc-clang 0278c78685d247a92d60d163e6cbd9fa4a4441e4) (http://llvm.org/git/llvm git@github.com:llvm-mirror/llvm 40d734de4c19a34d2d1764b136470ee25993eb4e)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Dump of assembler code for function func1:
   0x00000000004005a0 <+0>:	 c6 05 69 14 00 00 ff	movb   $0xff,0x1469(%rip)        # 0x401a10 <buf>
   0x00000000004005a7 <+7>:	 c6 05 63 14 00 00 ff	movb   $0xff,0x1463(%rip)        # 0x401a11 <buf+1>
   0x00000000004005ae <+14>:	 c6 05 5d 14 00 00 ff	movb   $0xff,0x145d(%rip)        # 0x401a12 <buf+2>
   0x00000000004005b5 <+21>:	 c6 05 57 14 00 00 ff	movb   $0xff,0x1457(%rip)        # 0x401a13 <buf+3>
   0x00000000004005bc <+28>:	 c6 05 51 14 00 00 ff	movb   $0xff,0x1451(%rip)        # 0x401a14 <buf+4>
   0x00000000004005c3 <+35>:	 c6 05 4b 14 00 00 ff	movb   $0xff,0x144b(%rip)        # 0x401a15 <buf+5>
   0x00000000004005ca <+42>:	 c6 05 45 14 00 00 ff	movb   $0xff,0x1445(%rip)        # 0x401a16 <buf+6>
   0x00000000004005d1 <+49>:	 c6 05 3f 14 00 00 ff	movb   $0xff,0x143f(%rip)        # 0x401a17 <buf+7>
   0x00000000004005d8 <+56>:	 c6 05 39 14 00 00 ff	movb   $0xff,0x1439(%rip)        # 0x401a18 <buf+8>
   0x00000000004005df <+63>:	 c6 05 33 14 00 00 ff	movb   $0xff,0x1433(%rip)        # 0x401a19 <buf+9>
   0x00000000004005e6 <+70>:	 c6 05 2d 14 00 00 ff	movb   $0xff,0x142d(%rip)        # 0x401a1a <buf+10>
   0x00000000004005ed <+77>:	 c6 05 27 14 00 00 ff	movb   $0xff,0x1427(%rip)        # 0x401a1b <buf+11>
   0x00000000004005f4 <+84>:	 c6 05 21 14 00 00 ff	movb   $0xff,0x1421(%rip)        # 0x401a1c <buf+12>
   0x00000000004005fb <+91>:	 c6 05 1b 14 00 00 ff	movb   $0xff,0x141b(%rip)        # 0x401a1d <buf+13>
   0x0000000000400602 <+98>:	 c6 05 15 14 00 00 ff	movb   $0xff,0x1415(%rip)        # 0x401a1e <buf+14>
   0x0000000000400609 <+105>:	 c6 05 0f 14 00 00 ff	movb   $0xff,0x140f(%rip)        # 0x401a1f <buf+15>
   0x0000000000400610 <+112>:	 c3	retq   
End of assembler dump.
Dump of assembler code for function func2:
   0x00000000004005a0 <+0>:	 c7 05 16 14 00 00 ff ff ff ff	movl   $0xffffffff,0x1416(%rip)        # 0x4019c0 <buf>
   0x00000000004005aa <+10>:	 c7 05 10 14 00 00 ff ff ff ff	movl   $0xffffffff,0x1410(%rip)        # 0x4019c4 <buf+4>
   0x00000000004005b4 <+20>:	 c7 05 0a 14 00 00 ff ff ff ff	movl   $0xffffffff,0x140a(%rip)        # 0x4019c8 <buf+8>
   0x00000000004005be <+30>:	 c7 05 04 14 00 00 ff ff ff ff	movl   $0xffffffff,0x1404(%rip)        # 0x4019cc <buf+12>
   0x00000000004005c8 <+40>:	 c3	retq   
End of assembler dump.
Dump of assembler code for function func3:
   0x00000000004005a0 <+0>:	 48 c7 05 05 14 00 00 ff ff ff ff	movq   $0xffffffffffffffff,0x1405(%rip)        # 0x4019b0 <buf>
   0x00000000004005ab <+11>:	 48 c7 05 02 14 00 00 ff ff ff ff	movq   $0xffffffffffffffff,0x1402(%rip)        # 0x4019b8 <buf+8>
   0x00000000004005b6 <+22>:	 c3	retq   
End of assembler dump.

=== Func1 Timing ===

real	0m20.440s
user	0m20.410s
sys	0m0.000s
=== Func2 Timing ===

real	0m8.418s
user	0m8.404s
sys	0m0.001s
=== Func3 Timing ===

real	0m7.217s
user	0m7.196s
sys	0m0.002s

Bug: http://llvm.org/bugs/show_bug.cgi?id=13836 .

Fixed in r163809!

Updated log from mainline:

clang version 3.2 (http://llvm.org/git/clang.git git@github.com:dtzWill/ioc-clang 0278c78685d247a92d60d163e6cbd9fa4a4441e4) (http://llvm.org/git/llvm git@github.com:llvm-mirror/llvm 629956400519d7b66c2009aed3a85c737018dc5b)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Dump of assembler code for function func1:
0x00000000004005a0 <+0>: 48 c7 05 0d 14 00 00 ff ff ff ff movq $0xffffffffffffffff,0x140d(%rip) # 0x4019b8 <buf+8>
0x00000000004005ab <+11>: 48 c7 05 fa 13 00 00 ff ff ff ff movq $0xffffffffffffffff,0x13fa(%rip) # 0x4019b0
0x00000000004005b6 <+22>: c3 retq
End of assembler dump.
Dump of assembler code for function func2:
0x00000000004005a0 <+0>: 48 c7 05 0d 14 00 00 ff ff ff ff movq $0xffffffffffffffff,0x140d(%rip) # 0x4019b8 <buf+8>
0x00000000004005ab <+11>: 48 c7 05 fa 13 00 00 ff ff ff ff movq $0xffffffffffffffff,0x13fa(%rip) # 0x4019b0
0x00000000004005b6 <+22>: c3 retq
End of assembler dump.
Dump of assembler code for function func3:
0x00000000004005a0 <+0>: 48 c7 05 0d 14 00 00 ff ff ff ff movq $0xffffffffffffffff,0x140d(%rip) # 0x4019b8 <buf+8>
0x00000000004005ab <+11>: 48 c7 05 fa 13 00 00 ff ff ff ff movq $0xffffffffffffffff,0x13fa(%rip) # 0x4019b0
0x00000000004005b6 <+22>: c3 retq
End of assembler dump.

=== Func1 Timing ===

real 0m7.263s
user 0m7.251s
sys 0m0.001s
=== Func2 Timing ===

real 0m7.219s
user 0m7.208s
sys 0m0.000s
=== Func3 Timing ===

real 0m7.218s
user 0m7.206s
sys 0m0.001s

Perfect!