diff options
Diffstat (limited to 'compiler/rustc_codegen_ssa/src/traits')
| -rw-r--r-- | compiler/rustc_codegen_ssa/src/traits/builder.rs | 157 | ||||
| -rw-r--r-- | compiler/rustc_codegen_ssa/src/traits/consts.rs | 1 |
2 files changed, 3 insertions, 155 deletions
diff --git a/compiler/rustc_codegen_ssa/src/traits/builder.rs b/compiler/rustc_codegen_ssa/src/traits/builder.rs index 9f49749bb..10cf8948b 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::operand::OperandRef; 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 @@ pub trait BuilderMethods<'a, 'tcx>: 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 @@ pub trait BuilderMethods<'a, 'tcx>: 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; diff --git a/compiler/rustc_codegen_ssa/src/traits/consts.rs b/compiler/rustc_codegen_ssa/src/traits/consts.rs index 8a91d4735..fdc7a30e8 100644 --- a/compiler/rustc_codegen_ssa/src/traits/consts.rs +++ b/compiler/rustc_codegen_ssa/src/traits/consts.rs @@ -29,7 +29,6 @@ pub trait ConstMethods<'tcx>: BackendTypes { fn const_data_from_alloc(&self, alloc: ConstAllocation<'tcx>) -> Self::Value; fn scalar_to_backend(&self, cv: Scalar, layout: abi::Scalar, llty: Self::Type) -> Self::Value; - fn zst_to_backend(&self, llty: Self::Type) -> Self::Value; fn from_const_alloc( &self, layout: TyAndLayout<'tcx>, |