Remove packed_struct dependency; closes #1271 and #1284 (#1282)

cranelift/codegen/shared/src/isa/x86/encoding_bits.rs

@@ -1,6 +1,6 @@
 //! Provides a named interface to the `u16` Encoding bits.
 
-use packed_struct::prelude::*;
+use std::ops::RangeInclusive;
 
 /// Named interface to the `u16` Encoding bits, representing an opcode.
 ///
@@ -27,61 +27,103 @@ use packed_struct::prelude::*;
 ///        11: 0F 3A <op>  (Op3/Mp3)
 /// 12-14  rrr, opcode bits for the ModR/M byte for certain opcodes.
 /// 15:    REX.W bit (or VEX.W/E)
-#[derive(Copy, Clone, PartialEq, PackedStruct)]
-#[packed_struct(size_bytes = "2", bit_numbering = "lsb0")]
-pub struct EncodingBits {
-    /// Instruction opcode byte, without the prefix.
-    #[packed_field(bits = "0:7")]
-    pub opcode_byte: u8,
-
-    /// Prefix kind for the instruction, as an enum.
-    #[packed_field(bits = "8:11", ty = "enum")]
-    pub prefix: OpcodePrefix,
-
-    /// Bits for the ModR/M byte for certain opcodes.
-    #[packed_field(bits = "12:14")]
-    pub rrr: Integer<u8, packed_bits::Bits3>,
-
-    /// REX.W bit (or VEX.W/E).
-    #[packed_field(bits = "15")]
-    pub rex_w: Integer<u8, packed_bits::Bits1>,
-}
+#[derive(Copy, Clone, PartialEq)]
+pub struct EncodingBits(u16);
+const OPCODE: RangeInclusive<u16> = 0..=7;
+const OPCODE_PREFIX: RangeInclusive<u16> = 8..=11; // Includes pp and mm.
+const RRR: RangeInclusive<u16> = 12..=14;
+const REX_W: RangeInclusive<u16> = 15..=15;
 
 impl From<u16> for EncodingBits {
-    fn from(bits: u16) -> EncodingBits {
-        let bytes: [u8; 2] = [((bits >> 8) & 0xff) as u8, (bits & 0xff) as u8];
-        EncodingBits::unpack(&bytes).expect("failed creating EncodingBits")
+    fn from(bits: u16) -> Self {
+        Self(bits)
     }
 }
 
 impl EncodingBits {
     /// Constructs a new EncodingBits from parts.
     pub fn new(op_bytes: &[u8], rrr: u16, rex_w: u16) -> Self {
-        EncodingBits {
-            opcode_byte: op_bytes[op_bytes.len() - 1],
-            prefix: OpcodePrefix::from_opcode(op_bytes),
-            rrr: (rrr as u8).into(),
-            rex_w: (rex_w as u8).into(),
-        }
+        assert!(
+            !op_bytes.is_empty(),
+            "op_bytes must include at least one opcode byte"
+        );
+        let mut new = Self::from(0);
+        let last_byte = op_bytes[op_bytes.len() - 1];
+        new.write(OPCODE, last_byte as u16);
+        let prefix: u8 = OpcodePrefix::from_opcode(op_bytes).into();
+        new.write(OPCODE_PREFIX, prefix as u16);
+        new.write(RRR, rrr);
+        new.write(REX_W, rex_w);
+        new
     }
 
     /// Returns the raw bits.
     #[inline]
     pub fn bits(self) -> u16 {
-        let bytes: [u8; 2] = self.pack();
-        ((bytes[0] as u16) << 8) | (bytes[1] as u16)
+        self.0
+    }
+
+    /// Convenience method for writing bits to specific range.
+    #[inline]
+    fn write(&mut self, range: RangeInclusive<u16>, value: u16) {
+        assert!(ExactSizeIterator::len(&range) > 0);
+        let size = range.end() - range.start() + 1; // Calculate the number of bits in the range.
+        let mask = (1 << size) - 1; // Generate a bit mask.
+        debug_assert!(
+            value <= mask,
+            "The written value should have fewer than {} bits.",
+            size
+        );
+        let mask_complement = !(mask << *range.start()); // Create the bitwise complement for the clear mask.
+        self.0 &= mask_complement; // Clear the bits in `range`.
+        let value = (value & mask) << *range.start(); // Place the value in the correct location.
+        self.0 |= value; // Modify the bits in `range`.
+    }
+
+    /// Convenience method for reading bits from a specific range.
+    #[inline]
+    fn read(self, range: RangeInclusive<u16>) -> u8 {
+        assert!(ExactSizeIterator::len(&range) > 0);
+        let size = range.end() - range.start() + 1; // Calculate the number of bits in the range.
+        debug_assert!(size <= 8, "This structure expects ranges of at most 8 bits");
+        let mask = (1 << size) - 1; // Generate a bit mask.
+        ((self.0 >> *range.start()) & mask) as u8
+    }
+
+    /// Instruction opcode byte, without the prefix.
+    #[inline]
+    pub fn opcode_byte(self) -> u8 {
+        self.read(OPCODE)
+    }
+
+    /// Prefix kind for the instruction, as an enum.
+    #[inline]
+    pub fn prefix(self) -> OpcodePrefix {
+        OpcodePrefix::from(self.read(OPCODE_PREFIX))
     }
 
     /// Extracts the PP bits of the OpcodePrefix.
     #[inline]
     pub fn pp(self) -> u8 {
-        self.prefix.to_primitive() & 0x3
+        self.prefix().to_primitive() & 0x3
     }
 
     /// Extracts the MM bits of the OpcodePrefix.
     #[inline]
     pub fn mm(self) -> u8 {
-        (self.prefix.to_primitive() >> 2) & 0x3
+        (self.prefix().to_primitive() >> 2) & 0x3
+    }
+
+    /// Bits for the ModR/M byte for certain opcodes.
+    #[inline]
+    pub fn rrr(self) -> u8 {
+        self.read(RRR)
+    }
+
+    /// REX.W bit (or VEX.W/E).
+    #[inline]
+    pub fn rex_w(self) -> u8 {
+        self.read(REX_W)
     }
 }
 
@@ -90,55 +132,103 @@ impl EncodingBits {
 /// The prefix type occupies four of the EncodingBits.
 #[allow(non_camel_case_types)]
 #[allow(missing_docs)]
-#[derive(Copy, Clone, Debug, Eq, PartialEq, PrimitiveEnum_u8)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub enum OpcodePrefix {
-    Op1 = 0b0000,
-    Mp1_66 = 0b0001,
-    Mp1_f3 = 0b0010,
-    Mp1_f2 = 0b0011,
-    Op2_0f = 0b0100,
-    Mp2_66_0f = 0b0101,
-    Mp2_f3_0f = 0b0110,
-    Mp2_f2_0f = 0b0111,
-    Op3_0f_38 = 0b1000,
-    Mp3_66_0f_38 = 0b1001,
-    Mp3_f3_0f_38 = 0b1010,
-    Mp3_f2_0f_38 = 0b1011,
-    Op3_0f_3a = 0b1100,
-    Mp3_66_0f_3a = 0b1101,
-    Mp3_f3_0f_3a = 0b1110,
-    Mp3_f2_0f_3a = 0b1111,
+    Op1,
+    Mp1_66,
+    Mp1_f3,
+    Mp1_f2,
+    Op2_0f,
+    Mp2_66_0f,
+    Mp2_f3_0f,
+    Mp2_f2_0f,
+    Op3_0f_38,
+    Mp3_66_0f_38,
+    Mp3_f3_0f_38,
+    Mp3_f2_0f_38,
+    Op3_0f_3a,
+    Mp3_66_0f_3a,
+    Mp3_f3_0f_3a,
+    Mp3_f2_0f_3a,
 }
 
 impl From<u8> for OpcodePrefix {
-    fn from(n: u8) -> OpcodePrefix {
-        OpcodePrefix::from_primitive(n).expect("invalid OpcodePrefix")
+    fn from(n: u8) -> Self {
+        use OpcodePrefix::*;
+        match n {
+            0b0000 => Op1,
+            0b0001 => Mp1_66,
+            0b0010 => Mp1_f3,
+            0b0011 => Mp1_f2,
+            0b0100 => Op2_0f,
+            0b0101 => Mp2_66_0f,
+            0b0110 => Mp2_f3_0f,
+            0b0111 => Mp2_f2_0f,
+            0b1000 => Op3_0f_38,
+            0b1001 => Mp3_66_0f_38,
+            0b1010 => Mp3_f3_0f_38,
+            0b1011 => Mp3_f2_0f_38,
+            0b1100 => Op3_0f_3a,
+            0b1101 => Mp3_66_0f_3a,
+            0b1110 => Mp3_f3_0f_3a,
+            0b1111 => Mp3_f2_0f_3a,
+            _ => panic!("invalid opcode prefix"),
+        }
+    }
+}
+
+impl Into<u8> for OpcodePrefix {
+    fn into(self) -> u8 {
+        use OpcodePrefix::*;
+        match self {
+            Op1 => 0b0000,
+            Mp1_66 => 0b0001,
+            Mp1_f3 => 0b0010,
+            Mp1_f2 => 0b0011,
+            Op2_0f => 0b0100,
+            Mp2_66_0f => 0b0101,
+            Mp2_f3_0f => 0b0110,
+            Mp2_f2_0f => 0b0111,
+            Op3_0f_38 => 0b1000,
+            Mp3_66_0f_38 => 0b1001,
+            Mp3_f3_0f_38 => 0b1010,
+            Mp3_f2_0f_38 => 0b1011,
+            Op3_0f_3a => 0b1100,
+            Mp3_66_0f_3a => 0b1101,
+            Mp3_f3_0f_3a => 0b1110,
+            Mp3_f2_0f_3a => 0b1111,
+        }
     }
 }
 
 impl OpcodePrefix {
+    /// Convert an opcode prefix to a `u8`; this is a convenience proxy for `Into<u8>`.
+    fn to_primitive(self) -> u8 {
+        self.into()
+    }
+
     /// Extracts the OpcodePrefix from the opcode.
-    pub fn from_opcode(op_bytes: &[u8]) -> OpcodePrefix {
+    pub fn from_opcode(op_bytes: &[u8]) -> Self {
         assert!(!op_bytes.is_empty(), "at least one opcode byte");
 
         let prefix_bytes = &op_bytes[..op_bytes.len() - 1];
         match prefix_bytes {
-            [] => OpcodePrefix::Op1,
-            [0x66] => OpcodePrefix::Mp1_66,
-            [0xf3] => OpcodePrefix::Mp1_f3,
-            [0xf2] => OpcodePrefix::Mp1_f2,
-            [0x0f] => OpcodePrefix::Op2_0f,
-            [0x66, 0x0f] => OpcodePrefix::Mp2_66_0f,
-            [0xf3, 0x0f] => OpcodePrefix::Mp2_f3_0f,
-            [0xf2, 0x0f] => OpcodePrefix::Mp2_f2_0f,
-            [0x0f, 0x38] => OpcodePrefix::Op3_0f_38,
-            [0x66, 0x0f, 0x38] => OpcodePrefix::Mp3_66_0f_38,
-            [0xf3, 0x0f, 0x38] => OpcodePrefix::Mp3_f3_0f_38,
-            [0xf2, 0x0f, 0x38] => OpcodePrefix::Mp3_f2_0f_38,
-            [0x0f, 0x3a] => OpcodePrefix::Op3_0f_3a,
-            [0x66, 0x0f, 0x3a] => OpcodePrefix::Mp3_66_0f_3a,
-            [0xf3, 0x0f, 0x3a] => OpcodePrefix::Mp3_f3_0f_3a,
-            [0xf2, 0x0f, 0x3a] => OpcodePrefix::Mp3_f2_0f_3a,
+            [] => Self::Op1,
+            [0x66] => Self::Mp1_66,
+            [0xf3] => Self::Mp1_f3,
+            [0xf2] => Self::Mp1_f2,
+            [0x0f] => Self::Op2_0f,
+            [0x66, 0x0f] => Self::Mp2_66_0f,
+            [0xf3, 0x0f] => Self::Mp2_f3_0f,
+            [0xf2, 0x0f] => Self::Mp2_f2_0f,
+            [0x0f, 0x38] => Self::Op3_0f_38,
+            [0x66, 0x0f, 0x38] => Self::Mp3_66_0f_38,
+            [0xf3, 0x0f, 0x38] => Self::Mp3_f3_0f_38,
+            [0xf2, 0x0f, 0x38] => Self::Mp3_f2_0f_38,
+            [0x0f, 0x3a] => Self::Op3_0f_3a,
+            [0x66, 0x0f, 0x3a] => Self::Mp3_66_0f_3a,
+            [0xf3, 0x0f, 0x3a] => Self::Mp3_f3_0f_3a,
+            [0xf2, 0x0f, 0x3a] => Self::Mp3_f2_0f_3a,
             _ => {
                 panic!("unexpected opcode sequence: {:?}", op_bytes);
             }
@@ -193,38 +283,93 @@ mod tests {
         test_roundtrip(OpcodePrefix::Mp3_f2_0f_3a);
     }
 
+    #[test]
+    fn prefix_to_name() {
+        assert_eq!(OpcodePrefix::Op1.recipe_name_prefix(), "Op1");
+        assert_eq!(OpcodePrefix::Op2_0f.recipe_name_prefix(), "Op2");
+        assert_eq!(OpcodePrefix::Op3_0f_38.recipe_name_prefix(), "Op3");
+        assert_eq!(OpcodePrefix::Mp1_66.recipe_name_prefix(), "Mp1");
+        assert_eq!(OpcodePrefix::Mp2_66_0f.recipe_name_prefix(), "Mp2");
+        assert_eq!(OpcodePrefix::Mp3_66_0f_3a.recipe_name_prefix(), "Mp3");
+    }
+
     /// Tests that the opcode_byte is the lower of the EncodingBits.
     #[test]
     fn encodingbits_opcode_byte() {
         let enc = EncodingBits::from(0x00ff);
-        assert_eq!(enc.opcode_byte, 0xff);
-        assert_eq!(enc.prefix.to_primitive(), 0x0);
-        assert_eq!(u8::from(enc.rrr), 0x0);
-        assert_eq!(u8::from(enc.rex_w), 0x0);
+        assert_eq!(enc.opcode_byte(), 0xff);
+        assert_eq!(enc.prefix().to_primitive(), 0x0);
+        assert_eq!(enc.rrr(), 0x0);
+        assert_eq!(enc.rex_w(), 0x0);
 
         let enc = EncodingBits::from(0x00cd);
-        assert_eq!(enc.opcode_byte, 0xcd);
+        assert_eq!(enc.opcode_byte(), 0xcd);
     }
 
     /// Tests that the OpcodePrefix is encoded correctly.
     #[test]
     fn encodingbits_prefix() {
         let enc = EncodingBits::from(0x0c00);
-        assert_eq!(enc.opcode_byte, 0x00);
-        assert_eq!(enc.prefix.to_primitive(), 0xc);
-        assert_eq!(enc.prefix, OpcodePrefix::Op3_0f_3a);
-        assert_eq!(u8::from(enc.rrr), 0x0);
-        assert_eq!(u8::from(enc.rex_w), 0x0);
+        assert_eq!(enc.opcode_byte(), 0x00);
+        assert_eq!(enc.prefix().to_primitive(), 0xc);
+        assert_eq!(enc.prefix(), OpcodePrefix::Op3_0f_3a);
+        assert_eq!(enc.rrr(), 0x0);
+        assert_eq!(enc.rex_w(), 0x0);
+    }
+
+    /// Tests that the PP bits are encoded correctly.
+    #[test]
+    fn encodingbits_pp() {
+        let enc = EncodingBits::from(0x0300);
+        assert_eq!(enc.opcode_byte(), 0x0);
+        assert_eq!(enc.pp(), 0x3);
+        assert_eq!(enc.mm(), 0x0);
+        assert_eq!(enc.rrr(), 0x0);
+        assert_eq!(enc.rex_w(), 0x0);
+    }
+
+    /// Tests that the MM bits are encoded correctly.
+    #[test]
+    fn encodingbits_mm() {
+        let enc = EncodingBits::from(0x0c00);
+        assert_eq!(enc.opcode_byte(), 0x0);
+        assert_eq!(enc.pp(), 0x00);
+        assert_eq!(enc.mm(), 0x3);
+        assert_eq!(enc.rrr(), 0x0);
+        assert_eq!(enc.rex_w(), 0x0);
+    }
+
+    /// Tests that the ModR/M bits are encoded correctly.
+    #[test]
+    fn encodingbits_rrr() {
+        let enc = EncodingBits::from(0x5000);
+        assert_eq!(enc.opcode_byte(), 0x0);
+        assert_eq!(enc.prefix().to_primitive(), 0x0);
+        assert_eq!(enc.rrr(), 0x5);
+        assert_eq!(enc.rex_w(), 0x0);
     }
 
     /// Tests that the REX.W bit is encoded correctly.
     #[test]
     fn encodingbits_rex_w() {
         let enc = EncodingBits::from(0x8000);
-        assert_eq!(enc.opcode_byte, 0x00);
-        assert_eq!(enc.prefix.to_primitive(), 0x0);
-        assert_eq!(u8::from(enc.rrr), 0x0);
-        assert_eq!(u8::from(enc.rex_w), 0x1);
+        assert_eq!(enc.opcode_byte(), 0x00);
+        assert_eq!(enc.prefix().to_primitive(), 0x0);
+        assert_eq!(enc.rrr(), 0x0);
+        assert_eq!(enc.rex_w(), 0x1);
+    }
+
+    /// Tests setting and unsetting a bit using EncodingBits::write.
+    #[test]
+    fn encodingbits_flip() {
+        let mut bits = EncodingBits::from(0);
+        let range = 2..=2;
+
+        bits.write(range.clone(), 1);
+        assert_eq!(bits.bits(), 0b100);
+
+        bits.write(range, 0);
+        assert_eq!(bits.bits(), 0b000);
     }
 
     /// Tests a round-trip of EncodingBits from/to a u16 (hardcoded endianness).
@@ -233,4 +378,26 @@ mod tests {
         let bits: u16 = 0x1234;
         assert_eq!(EncodingBits::from(bits).bits(), bits);
     }
+
+    #[test]
+    // I purposely want to divide the bits using the ranges defined above.
+    #[allow(clippy::inconsistent_digit_grouping)]
+    fn encodingbits_construction() {
+        assert_eq!(
+            EncodingBits::new(&[0x66, 0x40], 5, 1).bits(),
+            0b1_101_0001_01000000 // 1 = rex_w, 101 = rrr, 0001 = prefix, 01000000 = opcode
+        );
+    }
+
+    #[test]
+    #[should_panic]
+    fn encodingbits_panics_at_write_to_invalid_range() {
+        EncodingBits::from(0).write(1..=0, 42);
+    }
+
+    #[test]
+    #[should_panic]
+    fn encodingbits_panics_at_read_to_invalid_range() {
+        EncodingBits::from(0).read(1..=0);
+    }
 }