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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:03:36 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:03:36 +0000 |
commit | 17d40c6057c88f4c432b0d7bac88e1b84cb7e67f (patch) | |
tree | 3f66c4a5918660bb8a758ab6cda5ff8ee4f6cdcd /compiler/rustc_codegen_gcc/src/builder.rs | |
parent | Adding upstream version 1.64.0+dfsg1. (diff) | |
download | rustc-f7f0cc2a5d72e2c61c1f6900e70eec992bea4273.tar.xz rustc-f7f0cc2a5d72e2c61c1f6900e70eec992bea4273.zip |
Adding upstream version 1.65.0+dfsg1.upstream/1.65.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | compiler/rustc_codegen_gcc/src/builder.rs | 174 |
1 files changed, 169 insertions, 5 deletions
diff --git a/compiler/rustc_codegen_gcc/src/builder.rs b/compiler/rustc_codegen_gcc/src/builder.rs index 4d40dd099..6994eeb00 100644 --- a/compiler/rustc_codegen_gcc/src/builder.rs +++ b/compiler/rustc_codegen_gcc/src/builder.rs @@ -15,8 +15,11 @@ use gccjit::{ 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 @@ use rustc_codegen_ssa::traits::{ 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 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> { 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 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> { } 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"); |