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PowerPC AltiVec source vector subnormal values are not flushed to zero
Description of problem:
AltiVec specifies that source and result vectors are flushed to zero (in NJ mode). Only result vectors are flushed to zero.
Steps to reproduce:
1. Compile the attached Rust program (e.g. `cargo +nightly build --target powerpc-unknown-linux-gnu`)
2. Run the program and expect assertions to pass.
3. See assertions fail.
Additional information:
See the offending Rust program:
```
#![feature(stdsimd, powerpc_target_feature)]
use std::arch::powerpc::*;
#[target_feature(enable = "altivec")]
unsafe fn add(x: f32, y: f32) -> f32 {
let array: [f32; 4] = unsafe { std::mem::transmute(vec_add(vec_splats(x), vec_splats(y))) };
array[0]
}
pub fn main() {
let result = unsafe { add(-1.0857398e-38, 0.) };
assert_eq!(result, 0.);
// if the input is flushed, the result will be +0
// if only the output is flushed, the result is -0
assert!(result.is_sign_positive());
}
```
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