miri/shims/x86/
bmi.rs

1use rustc_abi::CanonAbi;
2use rustc_middle::ty::Ty;
3use rustc_span::Symbol;
4use rustc_target::callconv::FnAbi;
5
6use crate::*;
7
8impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
9pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
10    fn emulate_x86_bmi_intrinsic(
11        &mut self,
12        link_name: Symbol,
13        abi: &FnAbi<'tcx, Ty<'tcx>>,
14        args: &[OpTy<'tcx>],
15        dest: &MPlaceTy<'tcx>,
16    ) -> InterpResult<'tcx, EmulateItemResult> {
17        let this = self.eval_context_mut();
18
19        // Prefix should have already been checked.
20        let unprefixed_name = link_name.as_str().strip_prefix("llvm.x86.bmi.").unwrap();
21
22        // The intrinsics are suffixed with the bit size of their operands.
23        let (is_64_bit, unprefixed_name) = if unprefixed_name.ends_with("64") {
24            (true, unprefixed_name.strip_suffix(".64").unwrap_or(""))
25        } else {
26            (false, unprefixed_name.strip_suffix(".32").unwrap_or(""))
27        };
28
29        // All intrinsics of the "bmi" namespace belong to the "bmi2" ISA extension.
30        // The exception is "bextr", which belongs to "bmi1".
31        let target_feature = if unprefixed_name == "bextr" { "bmi1" } else { "bmi2" };
32        this.expect_target_feature_for_intrinsic(link_name, target_feature)?;
33
34        if is_64_bit && this.tcx.sess.target.arch != "x86_64" {
35            return interp_ok(EmulateItemResult::NotSupported);
36        }
37
38        let [left, right] = this.check_shim(abi, CanonAbi::C, link_name, args)?;
39        let left = this.read_scalar(left)?;
40        let right = this.read_scalar(right)?;
41
42        let left = if is_64_bit { left.to_u64()? } else { u64::from(left.to_u32()?) };
43        let right = if is_64_bit { right.to_u64()? } else { u64::from(right.to_u32()?) };
44
45        let result = match unprefixed_name {
46            // Extract a contigous range of bits from an unsigned integer.
47            // https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_bextr_u32
48            "bextr" => {
49                let start = u32::try_from(right & 0xff).unwrap();
50                let len = u32::try_from((right >> 8) & 0xff).unwrap();
51                let shifted = left.checked_shr(start).unwrap_or(0);
52                // Keep the `len` lowest bits of `shifted`, or all bits if `len` is too big.
53                if len >= 64 { shifted } else { shifted & 1u64.wrapping_shl(len).wrapping_sub(1) }
54            }
55            // Create a copy of an unsigned integer with bits above a certain index cleared.
56            // https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_bzhi_u32
57            "bzhi" => {
58                let index = u32::try_from(right & 0xff).unwrap();
59                // Keep the `index` lowest bits of `left`, or all bits if `index` is too big.
60                if index >= 64 { left } else { left & 1u64.wrapping_shl(index).wrapping_sub(1) }
61            }
62            // Extract bit values of an unsigned integer at positions marked by a mask.
63            // https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_pext_u32
64            "pext" => {
65                let mut mask = right;
66                let mut i = 0u32;
67                let mut result = 0;
68                // Iterate over the mask one 1-bit at a time, from
69                // the least significant bit to the most significant bit.
70                while mask != 0 {
71                    // Extract the bit marked by the mask's least significant set bit
72                    // and put it at position `i` of the result.
73                    result |= u64::from(left & (1 << mask.trailing_zeros()) != 0) << i;
74                    i = i.wrapping_add(1);
75                    // Clear the least significant set bit.
76                    mask &= mask.wrapping_sub(1);
77                }
78                result
79            }
80            // Deposit bit values of an unsigned integer to positions marked by a mask.
81            // https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_pdep_u32
82            "pdep" => {
83                let mut mask = right;
84                let mut set = left;
85                let mut result = 0;
86                // Iterate over the mask one 1-bit at a time, from
87                // the least significant bit to the most significant bit.
88                while mask != 0 {
89                    // Put rightmost bit of `set` at the position of the current `mask` bit.
90                    result |= (set & 1) << mask.trailing_zeros();
91                    // Go to next bit of `set`.
92                    set >>= 1;
93                    // Clear the least significant set bit.
94                    mask &= mask.wrapping_sub(1);
95                }
96                result
97            }
98            _ => return interp_ok(EmulateItemResult::NotSupported),
99        };
100
101        let result = if is_64_bit {
102            Scalar::from_u64(result)
103        } else {
104            Scalar::from_u32(u32::try_from(result).unwrap())
105        };
106        this.write_scalar(result, dest)?;
107
108        interp_ok(EmulateItemResult::NeedsReturn)
109    }
110}
miri/shims/x86/bmi.rs

miri/shims/x86/
bmi.rs
