From 147032a61896db76e97bfde9fa0e711fd5e62b08 Mon Sep 17 00:00:00 2001 From: Josh Stone Date: Tue, 16 Aug 2022 15:46:17 -0700 Subject: [PATCH] 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. --- Cargo.lock | 1 - compiler/rustc_codegen_gcc/src/builder.rs | 174 +++++++++++++++++- compiler/rustc_codegen_gcc/src/lib.rs | 1 + compiler/rustc_codegen_llvm/src/builder.rs | 13 +- compiler/rustc_codegen_ssa/Cargo.toml | 1 - .../rustc_codegen_ssa/src/traits/builder.rs | 157 +--------------- 6 files changed, 177 insertions(+), 170 deletions(-) diff --git a/Cargo.lock b/Cargo.lock index 395f5a127bd..aabb04995eb 100644 --- a/Cargo.lock +++ b/Cargo.lock @@ -3721,7 +3721,6 @@ dependencies = [ "object 0.29.0", "pathdiff", "regex", - "rustc_apfloat", "rustc_arena", "rustc_ast", "rustc_attr", diff --git a/compiler/rustc_codegen_gcc/src/builder.rs b/compiler/rustc_codegen_gcc/src/builder.rs index 4d40dd0994d..6994eeb00c3 100644 --- a/compiler/rustc_codegen_gcc/src/builder.rs +++ b/compiler/rustc_codegen_gcc/src/builder.rs @@ -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> { - 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> { - 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"); diff --git a/compiler/rustc_codegen_gcc/src/lib.rs b/compiler/rustc_codegen_gcc/src/lib.rs index 8a206c0368f..223466fb9b5 100644 --- a/compiler/rustc_codegen_gcc/src/lib.rs +++ b/compiler/rustc_codegen_gcc/src/lib.rs @@ -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; diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs index 073feecb164..e7e373bf45d 100644 --- a/compiler/rustc_codegen_llvm/src/builder.rs +++ b/compiler/rustc_codegen_llvm/src/builder.rs @@ -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( diff --git a/compiler/rustc_codegen_ssa/Cargo.toml b/compiler/rustc_codegen_ssa/Cargo.toml index 46d6344dbb2..d868e3d56ba 100644 --- a/compiler/rustc_codegen_ssa/Cargo.toml +++ b/compiler/rustc_codegen_ssa/Cargo.toml @@ -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" } diff --git a/compiler/rustc_codegen_ssa/src/traits/builder.rs b/compiler/rustc_codegen_ssa/src/traits/builder.rs index 9f49749bb41..10cf8948b5a 100644 --- a/compiler/rustc_codegen_ssa/src/traits/builder.rs +++ b/compiler/rustc_codegen_ssa/src/traits/builder.rs @@ -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; - fn fptosi_sat(&mut self, val: Self::Value, dest_ty: Self::Type) -> Option; + 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;