[Bug c++/42920] New: gcc does not produce necessary vec_lvrx instructions

[ryan dot sammartino at gmail dot com]

In the following short program (preprocessed files will be attached), the
output is incorrect when compiled with

ppu-g++ -o bug -O3 bug.cpp -maltivec

I get the output:

0.000000 1.000000 2.000000 3.000000
0.000000 0.000000 0.000000 7.000000
0.000000 0.000000 0.000000 30.000000
0.000000 0.000000 0.000000 15.000000

I was expecting:

0.000000 1.000000 2.000000 3.000000
4.000000 5.000000 6.000000 7.000000
8.000000 9.000000 10.000000 11.000000
12.000000 13.000000 14.000000 15.000000


--- cut here ---
#include <altivec.h>
#include <cstdio>

struct mat
{
    vector float v0;
    vector float v1;
    vector float v2;
    vector float v3;
};

vector float load_vec_unaligned(const float* a)
{
    return vec_or(vec_lvlx(0, a), vec_lvrx(16, a));
}

mat load_unaligned(const float* a)
{
    mat m;
    m.v0 = load_vec_unaligned(a);
    m.v1 = load_vec_unaligned(a+4);
    m.v2 = load_vec_unaligned(a+8);
    m.v3 = load_vec_unaligned(a+12);
    return m;
}

int main()
{
    __attribute__((aligned(16)))
        float f[18] = {-12.0f,
                       0.0f, 1.0f, 2.0f, 3.0f,
                       4.0f, 5.0f, 6.0f, 7.0f,
                       8.0f, 9.0f, 10.0f, 11.0f,
                       12.0f, 13.0f, 14.0f, 15.0f,
                       -12.0f};

    const mat m = load_unaligned(&f[1]);

    union { vector float v; float f[4]; } u;

    u.v = m.v0;
    printf("%f %f %f %f\n", u.f[0], u.f[1], u.f[2], u.f[3]);
    u.v = m.v1;
    printf("%f %f %f %f\n", u.f[0], u.f[1], u.f[2], u.f[3]);
    u.v = m.v2;
    printf("%f %f %f %f\n", u.f[0], u.f[1], u.f[2], u.f[3]);
    u.v = m.v3;
    printf("%f %f %f %f\n", u.f[0], u.f[1], u.f[2], u.f[3]);
}
--- cut here ---

For some reason, the load_unaligned function compiles correctly but something
goes wrong during inlining, as the vor instructions are not correct.

If I mark load_unaligned with __attribute__((noinline)), or compile with -O2, I
get the expected output.


-- 
           Summary: gcc does not produce necessary vec_lvrx instructions
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ryan dot sammartino at gmail dot com
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: ppu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42920