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Improve documentation of splatted constants

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This commit is contained in:
Caleb Zulawski 2022-01-18 03:51:04 +00:00
parent 1d5bf6bc28
commit 49d36d733d
1 changed files with 28 additions and 26 deletions
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54
compiler/rustc_codegen_ssa/src/traits/builder.rs
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@ -279,32 +279,6 @@ pub trait BuilderMethods<'a, 'tcx>:
assert!(rounded_max.value.is_finite());
(rounded_min.value.to_bits(), rounded_max.value.to_bits())
};
let maybe_splat = |bx: &mut Self, val| {
if bx.cx().type_kind(dest_ty) == TypeKind::Vector {
bx.vector_splat(bx.vector_length(dest_ty), val)
} else {
val
}
};
let float_bits_to_llval = |bx: &mut Self, bits| {
let bits_llval = match float_width {
32 => bx.cx().const_u32(bits as u32),
64 => bx.cx().const_u64(bits as u64),
n => bug!("unsupported float width {}", n),
};
bx.bitcast(bits_llval, float_ty)
};
let (f_min, f_max) = match float_width {
32 => compute_clamp_bounds_single(signed, int_width),
64 => compute_clamp_bounds_double(signed, int_width),
n => bug!("unsupported float width {}", n),
};
let f_min = float_bits_to_llval(self, f_min);
let f_max = float_bits_to_llval(self, f_max);
let f_min = maybe_splat(self, f_min);
let f_max = maybe_splat(self, f_max);
// To implement saturation, we perform the following steps:
//
// 1. Cast x to an integer with fpto[su]i. This may result in undef.
@ -332,9 +306,37 @@ pub trait BuilderMethods<'a, 'tcx>:
// int_ty::MIN and therefore the return value of int_ty::MIN is correct.
// QED.
let float_bits_to_llval = |bx: &mut Self, bits| {
let bits_llval = match float_width {
32 => bx.cx().const_u32(bits as u32),
64 => bx.cx().const_u64(bits as u64),
n => bug!("unsupported float width {}", n),
};
bx.bitcast(bits_llval, float_ty)
};
let (f_min, f_max) = match float_width {
32 => compute_clamp_bounds_single(signed, int_width),
64 => compute_clamp_bounds_double(signed, int_width),
n => bug!("unsupported float width {}", n),
};
let f_min = float_bits_to_llval(self, f_min);
let f_max = float_bits_to_llval(self, f_max);
let int_max = self.cx().const_uint_big(int_ty, int_max(signed, int_width));
let int_min = self.cx().const_uint_big(int_ty, int_min(signed, int_width) as u128);
let zero = self.cx().const_uint(int_ty, 0);
// If we're working with vectors, constants must be "splatted": the constant is duplicated
// into each lane of the vector. The algorithm stays the same, we are just using the
// same constant across all lanes.
let maybe_splat = |bx: &mut Self, val| {
if bx.cx().type_kind(dest_ty) == TypeKind::Vector {
bx.vector_splat(bx.vector_length(dest_ty), val)
} else {
val
}
};
let f_min = maybe_splat(self, f_min);
let f_max = maybe_splat(self, f_max);
let int_max = maybe_splat(self, int_max);
let int_min = maybe_splat(self, int_min);
let zero = maybe_splat(self, zero);