I tried this code:
[build-dependencies]
cc = "1.0.83"
// /build.rs
fn main() {
cc::Build::new()
.compiler("/usr/bin/clang-16")
.file("./src/abc.c")
.opt_level(0)
.compile("abc");
}// /src/abc.c
float test() {
_Float16 y = 114;
float z = y;
return z;
}// /src/main.rs
extern "C" {
fn test() -> f32;
}
fn main() {
println!("{}", unsafe { test() });
}I expected to see this happen: It prints 114.
Instead, this happened: It prints an unknown value, 0.00017929077, -0.045898438 or other.
After debugging, I found both compiler_builtins and libgcc provide the symbol __extendhfsf2. __extendhfsf2 is a compiler-rt intrinsics for casting a _Float16 to float. In compiler_builtins, the only argument of __extendhfsf2 is passed in a general-proposed register, However, in libgcc, the only argument of __extendhfsf2 is passed in xmm.
related: llvm/llvm-project#56854
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rustc --version --verbose:
rustc 1.74.1 (a28077b28 2023-12-04)
binary: rustc
commit-hash: a28077b28a02b92985b3a3faecf92813155f1ea1
commit-date: 2023-12-04
host: x86_64-unknown-linux-gnu
release: 1.74.1
LLVM version: 17.0.4
I tried this code:
I expected to see this happen: It prints
114.Instead, this happened: It prints an unknown value,
0.00017929077,-0.045898438or other.After debugging, I found both
compiler_builtinsandlibgccprovide the symbol__extendhfsf2.__extendhfsf2is acompiler-rtintrinsics for casting a_Float16tofloat. Incompiler_builtins, the only argument of__extendhfsf2is passed in a general-proposed register, However, inlibgcc, the only argument of__extendhfsf2is passed inxmm.related: llvm/llvm-project#56854
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rustc --version --verbose: