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clarify the second arg to llvm.ctlz and cttz

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This commit is contained in:
Jubilee Young 2024-05-19 19:04:03 -07:00
parent 9557b903b8
commit 213351ae9e
1 changed files with 3 additions and 3 deletions
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6
compiler/rustc_codegen_llvm/src/intrinsic.rs
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@ -2368,16 +2368,16 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
// byte swap is no-op for i8/u8
sym::simd_bswap if int_size == 8 => Ok(args[0].immediate()),
sym::simd_ctlz | sym::simd_cttz => {
// this fun bonus i1 arg means "poison if the arg vector contains zero"
// for the (int, i1 immediate) pair, the second arg adds `(0, true) => poison`
let fn_ty = bx.type_func(&[vec_ty, bx.type_i1()], vec_ty);
let dont_poison_on_zero = bx.const_int(bx.type_i1(), 0);
let f = bx.declare_cfn(llvm_intrinsic, llvm::UnnamedAddr::No, fn_ty);
Ok(bx.call(
fn_ty,
None,
None,
f,
// simd_ctlz and simd_cttz are exposed to safe code, so let's not poison anything
&[args[0].immediate(), bx.const_int(bx.type_i1(), 0)],
&[args[0].immediate(), dont_poison_on_zero],
None,
None,
))