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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`."""
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