Add simd_as intrinsic

1 files changed, 176 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_ssa/src/traits/builder.rs b/compiler/rustc_codegen_ssa/src/traits/builder.rs
index 48d88095855..501544693f1 100644
--- a/compiler/rustc_codegen_ssa/src/traits/builder.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/builder.rs
@@ -1,18 +1,21 @@
 use super::abi::AbiBuilderMethods;
 use super::asm::AsmBuilderMethods;
+use super::consts::ConstMethods;
 use super::coverageinfo::CoverageInfoBuilderMethods;
 use super::debuginfo::DebugInfoBuilderMethods;
 use super::intrinsic::IntrinsicCallMethods;
-use super::type_::ArgAbiMethods;
+use super::misc::MiscMethods;
+use super::type_::{ArgAbiMethods, BaseTypeMethods};
 use super::{HasCodegen, StaticBuilderMethods};
 
 use crate::common::{
-    AtomicOrdering, AtomicRmwBinOp, IntPredicate, RealPredicate, SynchronizationScope,
+    AtomicOrdering, AtomicRmwBinOp, IntPredicate, RealPredicate, SynchronizationScope, TypeKind,
 };
 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;
@@ -202,6 +205,177 @@ pub trait BuilderMethods<'a, 'tcx>:
     fn intcast(&mut self, val: Self::Value, dest_ty: Self::Type, is_signed: bool) -> Self::Value;
     fn pointercast(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value;
 
+    fn cast_float_to_int(
+        &mut self,
+        signed: bool,
+        x: Self::Value,
+        dest_ty: Self::Type,
+    ) -> Self::Value {
+        let in_ty = self.cx().val_ty(x);
+        let (float_ty, int_ty) = if self.cx().type_kind(dest_ty) == TypeKind::Vector
+            && self.cx().type_kind(in_ty) == TypeKind::Vector
+        {
+            (self.cx().element_type(in_ty), self.cx().element_type(dest_ty))
+        } else {
+            (in_ty, dest_ty)
+        };
+        assert!(matches!(self.cx().type_kind(float_ty), TypeKind::Float | TypeKind::Double));
+        assert_eq!(self.cx().type_kind(int_ty), TypeKind::Integer);
+
+        if let Some(false) = self.cx().sess().opts.debugging_opts.saturating_float_casts {
+            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())
+        };
+
+        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.
+        // 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 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);
+        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
+        }
+    }
+
     fn icmp(&mut self, op: IntPredicate, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
     fn fcmp(&mut self, op: RealPredicate, lhs: Self::Value, rhs: Self::Value) -> Self::Value;