[Bug target/39442] New: In some cases __builtin_ia32_loadups generates a movaps instruction

["amanieu at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

gcc version 4.3.2 (Ubuntu 4.3.2-1ubuntu12)

This code causes an alignment fault because __builtin_ia32_loadups will
generate a movaps instruction instead of a movups instruction.

#include <xmmintrin.h>
void sse_func(__m128, __m128);
float *get_arg(int);

int main(void)
{
        sse_func(__builtin_ia32_loadups(get_arg(0)),
__builtin_ia32_loadups(get_arg(0)));
}

Disassembly:
        pushl   $0
        call    get_arg
        movaps  (%eax), %xmm0
        movups  %xmm0, 16(%esp)
        movl    $0, (%esp)
        call    get_arg
        movaps  16(%esp), %xmm1
        movups  (%eax), %xmm0
        call    sse_func
        addl    $40, %esp

get_arg() returns a non-aligned pointer, but it is loaded with movaps which
expects a 16-byte aligned pointer. movups should be used instead. Also, the
next instruction stores the SSE register to the stack which is already
guaranteed to be 16-byte aligned, but it uses movups, which should only be used
for non 16-byte aligned pointers.

Command-line:
gcc -O1 -march=i386 -msse -fomit-frame-pointer -S test.c -o -

Bug also occurs with -O2 and -O3, but not with -O0, and with -march=i486 and
-march=i586, but not with -march=i686. The bug disappears when
-fomit-frame-pointer is removed.

The bug also disappears when get_arg(int) is changed to get_arg(void):'

#include <xmmintrin.h>
void sse_func(__m128, __m128);
float *get_arg(void);

int main(void)
{
        sse_func(__builtin_ia32_loadups(get_arg()),
__builtin_ia32_loadups(get_arg()));
}


-- 
           Summary: In some cases __builtin_ia32_loadups generates a movaps
                    instruction
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: amanieu at gmail dot com
 GCC build triplet: i486-pc-linux-gnu
  GCC host triplet: i486-pc-linux-gnu
GCC target triplet: i486-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39442