id = 2865
title = "loongarch64: wrong implementation of `xvldi` instruction"
state = "closed"
created_at = "2025-03-16T17:39:40.541Z"
closed_at = "2025-03-17T12:59:28.649Z"
labels = ["target: loongarch"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/2865"
host-os = "Debian"
host-arch = "loongarch64 (default one)"
qemu-version = "qemu-loongarch64 version 9.2.2 (Debian 1:9.2.2+ds-1+b2)"
guest-os = "n/a"
guest-arch = "loongarch64 (default one)"
description = """Consider this sample program.

```c++
#include <cstdio>
#include <cstdint>
#include <lsxintrin.h>
#include <lasxintrin.h>

void dump_u32(__m256i x) {
    uint32_t tmp[32/4];
    __lasx_xvst(x, tmp, 0);
    putchar('[');
    for (int i=0; i < 32/4; i++) {
        if (i > 0) {
            putchar(' ');
        }

        printf("%08x", tmp[i]);
    }
    puts("]");
}

int main() {
    __m256i const1 = __lasx_xvldi(-3832);
    dump_u32(const1);
}
```

The magic constants here means: replicate in 32-bit words a byte (0x4) shifted left by 8. We should have a vector of words 0x800, and indeed, the program run on a real hardware prints expected:

```
[00000800 00000800 00000800 00000800 00000800 00000800 00000800 00000800]
```

The same program run under Qemu prints:

```
[08000800 00000000 08000800 00000000 08000800 00000000 08000800 00000000]
```"""
reproduce = "n/a"
additional = """I grabbed the latest sources, it seems there's bug in `target/loongarch/tcg/insn_trans/trans_vec.c.inc`, in function `vldi_get_value`.

```c
    case 1:
        /* data: {2{16'0, imm[7:0], 8'0}} */
        data = (t << 24) | (t << 8);
        break;
```

There should be `(t << (8+32)) | t << 8`."""