[Bug c/60220] New: Vectorization : simple loop : fails to vectorize

[Bug c/60220] New: Vectorization : simple loop : fails to vectorize

[harmeeksingh at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60220

            Bug ID: 60220
           Summary: Vectorization : simple loop : fails to vectorize
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: harmeeksingh at gmail dot com

#include <stdio.h>
#include <stdint.h>
#define FALSE ((char )0)

struct test
{
  int            *copy;
};
typedef struct test test;

void
foo(test  *__restrict c, unsigned int a, unsigned int num)
{
  unsigned int cnt;
  for (cnt = 0; cnt < num ; cnt++)
    c->copy[cnt] = FALSE;
  for (cnt = 0; cnt < num ; cnt++)
    printf("%u \n", c->copy[cnt]);
}



$ gcc -ggdb -O6 -march=native -pipe -fno-strict-aliasing -funroll-all-loops
-fpeel-loops -unroll-loops --param max-unroll-times=4 -ffast-math -fpeel-loops
-fwrapv -fPIC -pthread -rdynamic -DCLS=64 -mfpmath=sse -mmmx -msse -msse2
-msse3 -mssse3  -msse4.1 -msse4.2 -msse4 -ftree-vectorize
-ftree-vectorizer-verbose=7 -fgraphite-identity  -falign-functions=4
-falign-loops=4 -falign-jumps=4 -fexpensive-optimizations
-frerun-cse-after-loop -frerun-loop-opt -finline-functions -o /tmp/x.o -c
/tmp/x.c

Analyzing loop at /tmp/x.c:18

18: not vectorized: loop contains function calls or data references that cannot
be analyzed
Analyzing loop at /tmp/x.c:16

16: not vectorized: data ref analysis failed *D.2523_9 = 0;

16: not vectorized: data ref analysis failed *D.2523_9 = 0;

/tmp/x.c:13: note: vectorized 0 loops in function.

Gcc - version

$ gcc -v 
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.7.2/lto-wrapper
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 --disable-build-with-cxx
--disable-build-poststage1-with-cxx --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --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 4.7.2 20120921 (Red Hat 4.7.2-2) (GCC)

[Bug c/60220] Vectorization : simple loop : fails to vectorize

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60220

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
In GCC 4.9 (maybe even in 4.8), the loop is converted into memset by the time
the vectorizer gets around to the code.

[Bug c/60220] Vectorization : simple loop : fails to vectorize

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60220

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |WORKSFORME

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
It's vectorized with -fno-tree-loop-distribute-patterns since at least GCC 4.7
(the oldest still maintained release).

[Bug c/60220] Vectorization : simple loop : fails to vectorize

[harmeeksingh at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60220

--- Comment #3 from harmeeksingh at gmail dot com ---
It still does not vectorise after adding the recomended flag. But rewriting the
code the following way does. 

This is a bizare behavioir . My tests show that this is not an issue of gcc
rewriting it as a memset . If I change the value 0 to a array assignment it
still gives. From the output it does show that it is trying to assign FALSE. 

31: not vectorized: data ref analysis failed *D.2549_9 = 0;

31: not vectorized: data ref analysis failed *D.2549_9 = 0;

#include <stdio.h>
#include <stdint.h>
#define FALSE ((char )0)

struct test
{
  int            *copy;
};
typedef struct test test;

static inline 
foo1(int *a, unsigned int num)
{
  unsigned int cnt;
  for (cnt = 0; cnt < num ; cnt++)
    a[cnt] = FALSE;
}

typedef uintptr_t Datum;

void
foo(test  *__restrict c, unsigned int a, unsigned int num)
{
  foo1(c->copy, num); // This vectorizes. if we pass it to inline function 
}