id = 852
title = "ppc64le: possible SIMD issue casting double to int"
state = "closed"
created_at = "2022-02-01T21:40:52.901Z"
closed_at = "2022-03-21T15:27:21.718Z"
labels = ["Closed::Fixed", "accel: TCG", "target: ppc"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/852"
host-os = "Debian 11 \"bullseye\""
host-arch = "x86_64"
qemu-version = "6.1.0"
guest-os = "Debian unstable \"sid\""
guest-arch = "ppc64le"
description = """Working with numpy in a ppc64le VM, I ran into a strange double -to casting issue, specifically when casting an array of 1.0 values to 1 values. The numpy folks guided me to a small reproducible test case.

The attached [convert.c](/uploads/2dd7936f4defccf816ffee7c7c002e77/convert.c) creates double and int arrays of length `1 <= n <= 16`. The double array is filled with the value 1.0, and both arrays are passed to a function that converts the value.

With `-O2`, output is as expected (truncated here): 

```
i =  1:   1
i =  2:   1 1
i =  3:   1 1 1
i =  4:   1 1 1 1
i =  5:   1 1 1 1 1
i =  6:   1 1 1 1 1 1
```

With `-O3`, all values that fit into blocks of four become zero:
```
i =  1:   1
i =  2:   1 1
i =  3:   1 1 1
i =  4:   0 0 0 0
i =  5:   0 0 0 0 1
i =  6:   0 0 0 0 1 1
```

I tested this with executables compiled on a physical ppc64le host, where the issue is not reproducible."""
reproduce = """1. `gcc -O2 -o convert convert.c && ./convert`
2. `gcc -O3 -o convert convert.c && ./convert`"""
additional = "n/a"