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