Rollup merge of #100653 - cuviper:fptoint_sat, r=michaelwoerister,antoyo
Move the cast_float_to_int fallback code to GCC Now that we require at least LLVM 13, that codegen backend is always using its intrinsic `fptosi.sat` and `fptoui.sat` conversions, so it doesn't need the manual implementation. However, the GCC backend still needs it, so we can move all of that code down there.
This commit is contained in:
Dylan DPC
GitHub
commit
c57a932c3f
@ -3369,7 +3369,6 @@ dependencies = [
|
||||
"object 0.29.0",
|
||||
"pathdiff",
|
||||
"regex",
|
||||
"rustc_apfloat",
|
||||
"rustc_arena",
|
||||
"rustc_ast",
|
||||
"rustc_attr",
|
||||
|
||||
@ -15,8 +15,11 @@
|
||||
Type,
|
||||
UnaryOp,
|
||||
};
|
||||
use rustc_apfloat::{ieee, Float, Round, Status};
|
||||
use rustc_codegen_ssa::MemFlags;
|
||||
use rustc_codegen_ssa::common::{AtomicOrdering, AtomicRmwBinOp, IntPredicate, RealPredicate, SynchronizationScope};
|
||||
use rustc_codegen_ssa::common::{
|
||||
AtomicOrdering, AtomicRmwBinOp, IntPredicate, RealPredicate, SynchronizationScope, TypeKind,
|
||||
};
|
||||
use rustc_codegen_ssa::mir::operand::{OperandRef, OperandValue};
|
||||
use rustc_codegen_ssa::mir::place::PlaceRef;
|
||||
use rustc_codegen_ssa::traits::{
|
||||
@ -31,6 +34,7 @@
|
||||
StaticBuilderMethods,
|
||||
};
|
||||
use rustc_data_structures::fx::FxHashSet;
|
||||
use rustc_middle::bug;
|
||||
use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
|
||||
use rustc_middle::ty::layout::{FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasParamEnv, HasTyCtxt, LayoutError, LayoutOfHelpers, TyAndLayout};
|
||||
use rustc_span::Span;
|
||||
@ -1271,12 +1275,12 @@ fn to_immediate_scalar(&mut self, val: Self::Value, scalar: abi::Scalar) -> Self
|
||||
val
|
||||
}
|
||||
|
||||
fn fptoui_sat(&mut self, _val: RValue<'gcc>, _dest_ty: Type<'gcc>) -> Option<RValue<'gcc>> {
|
||||
None
|
||||
fn fptoui_sat(&mut self, val: RValue<'gcc>, dest_ty: Type<'gcc>) -> RValue<'gcc> {
|
||||
self.fptoint_sat(false, val, dest_ty)
|
||||
}
|
||||
|
||||
fn fptosi_sat(&mut self, _val: RValue<'gcc>, _dest_ty: Type<'gcc>) -> Option<RValue<'gcc>> {
|
||||
None
|
||||
fn fptosi_sat(&mut self, val: RValue<'gcc>, dest_ty: Type<'gcc>) -> RValue<'gcc> {
|
||||
self.fptoint_sat(true, val, dest_ty)
|
||||
}
|
||||
|
||||
fn instrprof_increment(&mut self, _fn_name: RValue<'gcc>, _hash: RValue<'gcc>, _num_counters: RValue<'gcc>, _index: RValue<'gcc>) {
|
||||
@ -1285,6 +1289,166 @@ fn instrprof_increment(&mut self, _fn_name: RValue<'gcc>, _hash: RValue<'gcc>, _
|
||||
}
|
||||
|
||||
impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
|
||||
fn fptoint_sat(&mut self, signed: bool, val: RValue<'gcc>, dest_ty: Type<'gcc>) -> RValue<'gcc> {
|
||||
let src_ty = self.cx.val_ty(val);
|
||||
let (float_ty, int_ty) = if self.cx.type_kind(src_ty) == TypeKind::Vector {
|
||||
assert_eq!(self.cx.vector_length(src_ty), self.cx.vector_length(dest_ty));
|
||||
(self.cx.element_type(src_ty), self.cx.element_type(dest_ty))
|
||||
} else {
|
||||
(src_ty, dest_ty)
|
||||
};
|
||||
|
||||
// FIXME(jistone): the following was originally the fallback SSA implementation, before LLVM 13
|
||||
// added native `fptosi.sat` and `fptoui.sat` conversions, but it was used by GCC as well.
|
||||
// Now that LLVM always relies on its own, the code has been moved to GCC, but the comments are
|
||||
// still LLVM-specific. This should be updated, and use better GCC specifics if possible.
|
||||
|
||||
let int_width = self.cx.int_width(int_ty);
|
||||
let float_width = self.cx.float_width(float_ty);
|
||||
// LLVM's fpto[su]i returns undef when the input val is infinite, NaN, or does not fit into the
|
||||
// destination integer type after rounding towards zero. This `undef` value can cause UB in
|
||||
// safe code (see issue #10184), so we implement a saturating conversion on top of it:
|
||||
// Semantically, the mathematical value of the input is rounded towards zero to the next
|
||||
// mathematical integer, and then the result is clamped into the range of the destination
|
||||
// integer type. Positive and negative infinity are mapped to the maximum and minimum value of
|
||||
// the destination integer type. NaN is mapped to 0.
|
||||
//
|
||||
// Define f_min and f_max as the largest and smallest (finite) floats that are exactly equal to
|
||||
// a value representable in int_ty.
|
||||
// They are exactly equal to int_ty::{MIN,MAX} if float_ty has enough significand bits.
|
||||
// Otherwise, int_ty::MAX must be rounded towards zero, as it is one less than a power of two.
|
||||
// int_ty::MIN, however, is either zero or a negative power of two and is thus exactly
|
||||
// representable. Note that this only works if float_ty's exponent range is sufficiently large.
|
||||
// f16 or 256 bit integers would break this property. Right now the smallest float type is f32
|
||||
// with exponents ranging up to 127, which is barely enough for i128::MIN = -2^127.
|
||||
// On the other hand, f_max works even if int_ty::MAX is greater than float_ty::MAX. Because
|
||||
// we're rounding towards zero, we just get float_ty::MAX (which is always an integer).
|
||||
// This already happens today with u128::MAX = 2^128 - 1 > f32::MAX.
|
||||
let int_max = |signed: bool, int_width: u64| -> u128 {
|
||||
let shift_amount = 128 - int_width;
|
||||
if signed { i128::MAX as u128 >> shift_amount } else { u128::MAX >> shift_amount }
|
||||
};
|
||||
let int_min = |signed: bool, int_width: u64| -> i128 {
|
||||
if signed { i128::MIN >> (128 - int_width) } else { 0 }
|
||||
};
|
||||
|
||||
let compute_clamp_bounds_single = |signed: bool, int_width: u64| -> (u128, u128) {
|
||||
let rounded_min =
|
||||
ieee::Single::from_i128_r(int_min(signed, int_width), Round::TowardZero);
|
||||
assert_eq!(rounded_min.status, Status::OK);
|
||||
let rounded_max =
|
||||
ieee::Single::from_u128_r(int_max(signed, int_width), Round::TowardZero);
|
||||
assert!(rounded_max.value.is_finite());
|
||||
(rounded_min.value.to_bits(), rounded_max.value.to_bits())
|
||||
};
|
||||
let compute_clamp_bounds_double = |signed: bool, int_width: u64| -> (u128, u128) {
|
||||
let rounded_min =
|
||||
ieee::Double::from_i128_r(int_min(signed, int_width), Round::TowardZero);
|
||||
assert_eq!(rounded_min.status, Status::OK);
|
||||
let rounded_max =
|
||||
ieee::Double::from_u128_r(int_max(signed, int_width), Round::TowardZero);
|
||||
assert!(rounded_max.value.is_finite());
|
||||
(rounded_min.value.to_bits(), rounded_max.value.to_bits())
|
||||
};
|
||||
// To implement saturation, we perform the following steps:
|
||||
//
|
||||
// 1. Cast val to an integer with fpto[su]i. This may result in undef.
|
||||
// 2. Compare val to f_min and f_max, and use the comparison results to select:
|
||||
// a) int_ty::MIN if val < f_min or val is NaN
|
||||
// b) int_ty::MAX if val > f_max
|
||||
// c) the result of fpto[su]i otherwise
|
||||
// 3. If val is NaN, return 0.0, otherwise return the result of step 2.
|
||||
//
|
||||
// This avoids resulting undef because values in range [f_min, f_max] by definition fit into the
|
||||
// destination type. It creates an undef temporary, but *producing* undef is not UB. Our use of
|
||||
// undef does not introduce any non-determinism either.
|
||||
// More importantly, the above procedure correctly implements saturating conversion.
|
||||
// Proof (sketch):
|
||||
// If val is NaN, 0 is returned by definition.
|
||||
// Otherwise, val is finite or infinite and thus can be compared with f_min and f_max.
|
||||
// This yields three cases to consider:
|
||||
// (1) if val in [f_min, f_max], the result of fpto[su]i is returned, which agrees with
|
||||
// saturating conversion for inputs in that range.
|
||||
// (2) if val > f_max, then val is larger than int_ty::MAX. This holds even if f_max is rounded
|
||||
// (i.e., if f_max < int_ty::MAX) because in those cases, nextUp(f_max) is already larger
|
||||
// than int_ty::MAX. Because val is larger than int_ty::MAX, the return value of int_ty::MAX
|
||||
// is correct.
|
||||
// (3) if val < f_min, then val is smaller than int_ty::MIN. As shown earlier, f_min exactly equals
|
||||
// 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);
|
||||
|
||||
// Step 1 ...
|
||||
let fptosui_result = if signed { self.fptosi(val, dest_ty) } else { self.fptoui(val, dest_ty) };
|
||||
let less_or_nan = self.fcmp(RealPredicate::RealULT, val, f_min);
|
||||
let greater = self.fcmp(RealPredicate::RealOGT, val, f_max);
|
||||
|
||||
// Step 2: We use two comparisons and two selects, with %s1 being the
|
||||
// result:
|
||||
// %less_or_nan = fcmp ult %val, %f_min
|
||||
// %greater = fcmp olt %val, %f_max
|
||||
// %s0 = select %less_or_nan, int_ty::MIN, %fptosi_result
|
||||
// %s1 = select %greater, int_ty::MAX, %s0
|
||||
// Note that %less_or_nan uses an *unordered* comparison. This
|
||||
// comparison is true if the operands are not comparable (i.e., if val is
|
||||
// NaN). The unordered comparison ensures that s1 becomes int_ty::MIN if
|
||||
// val is NaN.
|
||||
//
|
||||
// Performance note: Unordered comparison can be lowered to a "flipped"
|
||||
// comparison and a negation, and the negation can be merged into the
|
||||
// select. Therefore, it not necessarily any more expensive than an
|
||||
// ordered ("normal") comparison. Whether these optimizations will be
|
||||
// performed is ultimately up to the backend, but at least x86 does
|
||||
// perform them.
|
||||
let s0 = self.select(less_or_nan, int_min, fptosui_result);
|
||||
let s1 = self.select(greater, int_max, s0);
|
||||
|
||||
// Step 3: NaN replacement.
|
||||
// For unsigned types, the above step already yielded int_ty::MIN == 0 if val is NaN.
|
||||
// Therefore we only need to execute this step for signed integer types.
|
||||
if signed {
|
||||
// LLVM has no isNaN predicate, so we use (val == val) instead
|
||||
let cmp = self.fcmp(RealPredicate::RealOEQ, val, val);
|
||||
self.select(cmp, s1, zero)
|
||||
} else {
|
||||
s1
|
||||
}
|
||||
}
|
||||
|
||||
#[cfg(feature="master")]
|
||||
pub fn shuffle_vector(&mut self, v1: RValue<'gcc>, v2: RValue<'gcc>, mask: RValue<'gcc>) -> RValue<'gcc> {
|
||||
let struct_type = mask.get_type().is_struct().expect("mask of struct type");
|
||||
|
||||
@ -19,6 +19,7 @@
|
||||
#![warn(rust_2018_idioms)]
|
||||
#![warn(unused_lifetimes)]
|
||||
|
||||
extern crate rustc_apfloat;
|
||||
extern crate rustc_ast;
|
||||
extern crate rustc_codegen_ssa;
|
||||
extern crate rustc_data_structures;
|
||||
|
||||
@ -725,11 +725,11 @@ fn sext(&mut self, val: &'ll Value, dest_ty: &'ll Type) -> &'ll Value {
|
||||
unsafe { llvm::LLVMBuildSExt(self.llbuilder, val, dest_ty, UNNAMED) }
|
||||
}
|
||||
|
||||
fn fptoui_sat(&mut self, val: &'ll Value, dest_ty: &'ll Type) -> Option<&'ll Value> {
|
||||
fn fptoui_sat(&mut self, val: &'ll Value, dest_ty: &'ll Type) -> &'ll Value {
|
||||
self.fptoint_sat(false, val, dest_ty)
|
||||
}
|
||||
|
||||
fn fptosi_sat(&mut self, val: &'ll Value, dest_ty: &'ll Type) -> Option<&'ll Value> {
|
||||
fn fptosi_sat(&mut self, val: &'ll Value, dest_ty: &'ll Type) -> &'ll Value {
|
||||
self.fptoint_sat(true, val, dest_ty)
|
||||
}
|
||||
|
||||
@ -1429,12 +1429,7 @@ fn add_incoming_to_phi(&mut self, phi: &'ll Value, val: &'ll Value, bb: &'ll Bas
|
||||
}
|
||||
}
|
||||
|
||||
fn fptoint_sat(
|
||||
&mut self,
|
||||
signed: bool,
|
||||
val: &'ll Value,
|
||||
dest_ty: &'ll Type,
|
||||
) -> Option<&'ll Value> {
|
||||
fn fptoint_sat(&mut self, signed: bool, val: &'ll Value, dest_ty: &'ll Type) -> &'ll Value {
|
||||
let src_ty = self.cx.val_ty(val);
|
||||
let (float_ty, int_ty, vector_length) = if self.cx.type_kind(src_ty) == TypeKind::Vector {
|
||||
assert_eq!(self.cx.vector_length(src_ty), self.cx.vector_length(dest_ty));
|
||||
@ -1459,7 +1454,7 @@ fn fptoint_sat(
|
||||
format!("llvm.{}.sat.i{}.f{}", instr, int_width, float_width)
|
||||
};
|
||||
let f = self.declare_cfn(&name, llvm::UnnamedAddr::No, self.type_func(&[src_ty], dest_ty));
|
||||
Some(self.call(self.type_func(&[src_ty], dest_ty), f, &[val], None))
|
||||
self.call(self.type_func(&[src_ty], dest_ty), f, &[val], None)
|
||||
}
|
||||
|
||||
pub(crate) fn landing_pad(
|
||||
|
||||
@ -26,7 +26,6 @@ rustc_arena = { path = "../rustc_arena" }
|
||||
rustc_ast = { path = "../rustc_ast" }
|
||||
rustc_span = { path = "../rustc_span" }
|
||||
rustc_middle = { path = "../rustc_middle" }
|
||||
rustc_apfloat = { path = "../rustc_apfloat" }
|
||||
rustc_attr = { path = "../rustc_attr" }
|
||||
rustc_symbol_mangling = { path = "../rustc_symbol_mangling" }
|
||||
rustc_data_structures = { path = "../rustc_data_structures" }
|
||||
|
||||
@ -1,6 +1,5 @@
|
||||
use super::abi::AbiBuilderMethods;
|
||||
use super::asm::AsmBuilderMethods;
|
||||
use super::consts::ConstMethods;
|
||||
use super::coverageinfo::CoverageInfoBuilderMethods;
|
||||
use super::debuginfo::DebugInfoBuilderMethods;
|
||||
use super::intrinsic::IntrinsicCallMethods;
|
||||
@ -15,7 +14,6 @@
|
||||
use crate::mir::place::PlaceRef;
|
||||
use crate::MemFlags;
|
||||
|
||||
use rustc_apfloat::{ieee, Float, Round, Status};
|
||||
use rustc_middle::ty::layout::{HasParamEnv, TyAndLayout};
|
||||
use rustc_middle::ty::Ty;
|
||||
use rustc_span::Span;
|
||||
@ -188,8 +186,8 @@ fn inbounds_gep(
|
||||
|
||||
fn trunc(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value;
|
||||
fn sext(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value;
|
||||
fn fptoui_sat(&mut self, val: Self::Value, dest_ty: Self::Type) -> Option<Self::Value>;
|
||||
fn fptosi_sat(&mut self, val: Self::Value, dest_ty: Self::Type) -> Option<Self::Value>;
|
||||
fn fptoui_sat(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value;
|
||||
fn fptosi_sat(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value;
|
||||
fn fptoui(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value;
|
||||
fn fptosi(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value;
|
||||
fn uitofp(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value;
|
||||
@ -223,156 +221,7 @@ fn cast_float_to_int(
|
||||
return if signed { self.fptosi(x, dest_ty) } else { self.fptoui(x, dest_ty) };
|
||||
}
|
||||
|
||||
let try_sat_result =
|
||||
if signed { self.fptosi_sat(x, dest_ty) } else { self.fptoui_sat(x, dest_ty) };
|
||||
if let Some(try_sat_result) = try_sat_result {
|
||||
return try_sat_result;
|
||||
}
|
||||
|
||||
let int_width = self.cx().int_width(int_ty);
|
||||
let float_width = self.cx().float_width(float_ty);
|
||||
// LLVM's fpto[su]i returns undef when the input x is infinite, NaN, or does not fit into the
|
||||
// destination integer type after rounding towards zero. This `undef` value can cause UB in
|
||||
// safe code (see issue #10184), so we implement a saturating conversion on top of it:
|
||||
// Semantically, the mathematical value of the input is rounded towards zero to the next
|
||||
// mathematical integer, and then the result is clamped into the range of the destination
|
||||
// integer type. Positive and negative infinity are mapped to the maximum and minimum value of
|
||||
// the destination integer type. NaN is mapped to 0.
|
||||
//
|
||||
// Define f_min and f_max as the largest and smallest (finite) floats that are exactly equal to
|
||||
// a value representable in int_ty.
|
||||
// They are exactly equal to int_ty::{MIN,MAX} if float_ty has enough significand bits.
|
||||
// Otherwise, int_ty::MAX must be rounded towards zero, as it is one less than a power of two.
|
||||
// int_ty::MIN, however, is either zero or a negative power of two and is thus exactly
|
||||
// representable. Note that this only works if float_ty's exponent range is sufficiently large.
|
||||
// f16 or 256 bit integers would break this property. Right now the smallest float type is f32
|
||||
// with exponents ranging up to 127, which is barely enough for i128::MIN = -2^127.
|
||||
// On the other hand, f_max works even if int_ty::MAX is greater than float_ty::MAX. Because
|
||||
// we're rounding towards zero, we just get float_ty::MAX (which is always an integer).
|
||||
// This already happens today with u128::MAX = 2^128 - 1 > f32::MAX.
|
||||
let int_max = |signed: bool, int_width: u64| -> u128 {
|
||||
let shift_amount = 128 - int_width;
|
||||
if signed { i128::MAX as u128 >> shift_amount } else { u128::MAX >> shift_amount }
|
||||
};
|
||||
let int_min = |signed: bool, int_width: u64| -> i128 {
|
||||
if signed { i128::MIN >> (128 - int_width) } else { 0 }
|
||||
};
|
||||
|
||||
let compute_clamp_bounds_single = |signed: bool, int_width: u64| -> (u128, u128) {
|
||||
let rounded_min =
|
||||
ieee::Single::from_i128_r(int_min(signed, int_width), Round::TowardZero);
|
||||
assert_eq!(rounded_min.status, Status::OK);
|
||||
let rounded_max =
|
||||
ieee::Single::from_u128_r(int_max(signed, int_width), Round::TowardZero);
|
||||
assert!(rounded_max.value.is_finite());
|
||||
(rounded_min.value.to_bits(), rounded_max.value.to_bits())
|
||||
};
|
||||
let compute_clamp_bounds_double = |signed: bool, int_width: u64| -> (u128, u128) {
|
||||
let rounded_min =
|
||||
ieee::Double::from_i128_r(int_min(signed, int_width), Round::TowardZero);
|
||||
assert_eq!(rounded_min.status, Status::OK);
|
||||
let rounded_max =
|
||||
ieee::Double::from_u128_r(int_max(signed, int_width), Round::TowardZero);
|
||||
assert!(rounded_max.value.is_finite());
|
||||
(rounded_min.value.to_bits(), rounded_max.value.to_bits())
|
||||
};
|
||||
// To implement saturation, we perform the following steps:
|
||||
//
|
||||
// 1. Cast x to an integer with fpto[su]i. This may result in undef.
|
||||
// 2. Compare x to f_min and f_max, and use the comparison results to select:
|
||||
// a) int_ty::MIN if x < f_min or x is NaN
|
||||
// b) int_ty::MAX if x > f_max
|
||||
// c) the result of fpto[su]i otherwise
|
||||
// 3. If x is NaN, return 0.0, otherwise return the result of step 2.
|
||||
//
|
||||
// This avoids resulting undef because values in range [f_min, f_max] by definition fit into the
|
||||
// destination type. It creates an undef temporary, but *producing* undef is not UB. Our use of
|
||||
// undef does not introduce any non-determinism either.
|
||||
// More importantly, the above procedure correctly implements saturating conversion.
|
||||
// Proof (sketch):
|
||||
// If x is NaN, 0 is returned by definition.
|
||||
// Otherwise, x is finite or infinite and thus can be compared with f_min and f_max.
|
||||
// This yields three cases to consider:
|
||||
// (1) if x in [f_min, f_max], the result of fpto[su]i is returned, which agrees with
|
||||
// saturating conversion for inputs in that range.
|
||||
// (2) if x > f_max, then x is larger than int_ty::MAX. This holds even if f_max is rounded
|
||||
// (i.e., if f_max < int_ty::MAX) because in those cases, nextUp(f_max) is already larger
|
||||
// than int_ty::MAX. Because x is larger than int_ty::MAX, the return value of int_ty::MAX
|
||||
// is correct.
|
||||
// (3) if x < f_min, then x is smaller than int_ty::MIN. As shown earlier, f_min exactly equals
|
||||
// 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);
|
||||
|
||||
// Step 1 ...
|
||||
let fptosui_result = if signed { self.fptosi(x, dest_ty) } else { self.fptoui(x, dest_ty) };
|
||||
let less_or_nan = self.fcmp(RealPredicate::RealULT, x, f_min);
|
||||
let greater = self.fcmp(RealPredicate::RealOGT, x, f_max);
|
||||
|
||||
// Step 2: We use two comparisons and two selects, with %s1 being the
|
||||
// result:
|
||||
// %less_or_nan = fcmp ult %x, %f_min
|
||||
// %greater = fcmp olt %x, %f_max
|
||||
// %s0 = select %less_or_nan, int_ty::MIN, %fptosi_result
|
||||
// %s1 = select %greater, int_ty::MAX, %s0
|
||||
// Note that %less_or_nan uses an *unordered* comparison. This
|
||||
// comparison is true if the operands are not comparable (i.e., if x is
|
||||
// NaN). The unordered comparison ensures that s1 becomes int_ty::MIN if
|
||||
// x is NaN.
|
||||
//
|
||||
// Performance note: Unordered comparison can be lowered to a "flipped"
|
||||
// comparison and a negation, and the negation can be merged into the
|
||||
// select. Therefore, it not necessarily any more expensive than an
|
||||
// ordered ("normal") comparison. Whether these optimizations will be
|
||||
// performed is ultimately up to the backend, but at least x86 does
|
||||
// perform them.
|
||||
let s0 = self.select(less_or_nan, int_min, fptosui_result);
|
||||
let s1 = self.select(greater, int_max, s0);
|
||||
|
||||
// Step 3: NaN replacement.
|
||||
// For unsigned types, the above step already yielded int_ty::MIN == 0 if x is NaN.
|
||||
// Therefore we only need to execute this step for signed integer types.
|
||||
if signed {
|
||||
// LLVM has no isNaN predicate, so we use (x == x) instead
|
||||
let cmp = self.fcmp(RealPredicate::RealOEQ, x, x);
|
||||
self.select(cmp, s1, zero)
|
||||
} else {
|
||||
s1
|
||||
}
|
||||
if signed { self.fptosi_sat(x, dest_ty) } else { self.fptoui_sat(x, dest_ty) }
|
||||
}
|
||||
|
||||
fn icmp(&mut self, op: IntPredicate, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
|
||||
|
||||
Loading…
Reference in New Issue
Block a user