x64: Implement SIMD fma (#4474)

* x64: Add VEX Instruction Encoder

This uses a similar builder pattern to the EVEX Encoder.
Does not yet support memory accesses.

* x64: Add FMA Flag

* x64: Implement SIMD `fma`

* x64: Use 4 register Vex Inst

* x64: Reorder VEX pretty print args

cranelift/codegen/src/isa/x64/encoding/rex.rs

@@ -159,6 +159,7 @@ impl From<(OperandSize, Reg)> for RexFlags {
 /// Allows using the same opcode byte in different "opcode maps" to allow for more instruction
 /// encodings. See appendix A in the Intel Software Developer's Manual, volume 2A, for more details.
 #[allow(missing_docs)]
+#[derive(PartialEq)]
 pub enum OpcodeMap {
     None,
     _0F,
@@ -168,7 +169,7 @@ pub enum OpcodeMap {
 
 impl OpcodeMap {
     /// Normally the opcode map is specified as bytes in the instruction, but some x64 encoding
-    /// formats pack this information as bits in a prefix (e.g. EVEX).
+    /// formats pack this information as bits in a prefix (e.g. VEX / EVEX).
     pub(crate) fn bits(&self) -> u8 {
         match self {
             OpcodeMap::None => 0b00,
@@ -187,6 +188,7 @@ impl Default for OpcodeMap {
 
 /// We may need to include one or more legacy prefix bytes before the REX prefix.  This enum
 /// covers only the small set of possibilities that we actually need.
+#[derive(PartialEq)]
 pub enum LegacyPrefixes {
     /// No prefix bytes.
     None,

cranelift/codegen/src/isa/x64/encoding/vex.rs

@@ -1,2 +1,357 @@
 //! Encodes VEX instructions. These instructions are those added by the Advanced Vector Extensions
 //! (AVX).
+
+use super::evex::Register;
+use super::rex::{LegacyPrefixes, OpcodeMap};
+use super::ByteSink;
+use crate::isa::x64::encoding::rex::encode_modrm;
+
+/// Constructs a VEX-encoded instruction using a builder pattern. This approach makes it visually
+/// easier to transform something the manual's syntax, `VEX.128.66.0F 73 /7 ib` to code:
+/// `VexInstruction::new().length(...).prefix(...).map(...).w(true).opcode(0x1F).reg(...).rm(...)`.
+pub struct VexInstruction {
+    length: VexVectorLength,
+    prefix: LegacyPrefixes,
+    map: OpcodeMap,
+    opcode: u8,
+    w: bool,
+    reg: u8,
+    rm: Register,
+    vvvv: Option<Register>,
+    imm: Option<u8>,
+}
+
+impl Default for VexInstruction {
+    fn default() -> Self {
+        Self {
+            length: VexVectorLength::default(),
+            prefix: LegacyPrefixes::None,
+            map: OpcodeMap::None,
+            opcode: 0x00,
+            w: false,
+            reg: 0x00,
+            rm: Register::default(),
+            vvvv: None,
+            imm: None,
+        }
+    }
+}
+
+impl VexInstruction {
+    /// Construct a default VEX instruction.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Set the length of the instruction.
+    #[inline(always)]
+    pub fn length(mut self, length: VexVectorLength) -> Self {
+        self.length = length;
+        self
+    }
+
+    /// Set the legacy prefix byte of the instruction: None | 66 | F2 | F3. VEX instructions
+    /// pack these into the prefix, not as separate bytes.
+    #[inline(always)]
+    pub fn prefix(mut self, prefix: LegacyPrefixes) -> Self {
+        debug_assert!(
+            prefix == LegacyPrefixes::None
+                || prefix == LegacyPrefixes::_66
+                || prefix == LegacyPrefixes::_F2
+                || prefix == LegacyPrefixes::_F3
+        );
+
+        self.prefix = prefix;
+        self
+    }
+
+    /// Set the opcode map byte of the instruction: None | 0F | 0F38 | 0F3A. VEX instructions pack
+    /// these into the prefix, not as separate bytes.
+    #[inline(always)]
+    pub fn map(mut self, map: OpcodeMap) -> Self {
+        self.map = map;
+        self
+    }
+
+    /// Set the W bit, denoted by `.W1` or `.W0` in the instruction string.
+    /// Typically used to indicate an instruction using 64 bits of an operand (e.g.
+    /// 64 bit lanes). EVEX packs this bit in the EVEX prefix; previous encodings used the REX
+    /// prefix.
+    #[inline(always)]
+    pub fn w(mut self, w: bool) -> Self {
+        self.w = w;
+        self
+    }
+
+    /// Set the instruction opcode byte.
+    #[inline(always)]
+    pub fn opcode(mut self, opcode: u8) -> Self {
+        self.opcode = opcode;
+        self
+    }
+
+    /// Set the register to use for the `reg` bits; many instructions use this as the write operand.
+    #[inline(always)]
+    pub fn reg(mut self, reg: impl Into<Register>) -> Self {
+        self.reg = reg.into().into();
+        self
+    }
+
+    /// Some instructions use the ModRM.reg field as an opcode extension. This is usually denoted by
+    /// a `/n` field in the manual.
+    #[inline(always)]
+    pub fn opcode_ext(mut self, n: u8) -> Self {
+        self.reg = n;
+        self
+    }
+
+    /// Set the register to use for the `rm` bits; many instructions use this as the "read from
+    /// register/memory" operand. Currently this does not support memory addressing (TODO).Setting
+    /// this affects both the ModRM byte (`rm` section) and the VEX prefix (the extension bits for
+    /// register encodings > 8).
+    #[inline(always)]
+    pub fn rm(mut self, reg: impl Into<Register>) -> Self {
+        self.rm = reg.into();
+        self
+    }
+
+    /// Set the `vvvv` register; some instructions allow using this as a second, non-destructive
+    /// source register in 3-operand instructions (e.g. 2 read, 1 write).
+    #[allow(dead_code)]
+    #[inline(always)]
+    pub fn vvvv(mut self, reg: impl Into<Register>) -> Self {
+        self.vvvv = Some(reg.into());
+        self
+    }
+
+    /// Set the imm byte when used for a register. The reg bits are stored in `imm8[7:4]` with
+    /// the lower bits unused. Overrides a previously set [Self::imm] field.
+    #[inline(always)]
+    pub fn imm_reg(mut self, reg: impl Into<Register>) -> Self {
+        let reg: u8 = reg.into().into();
+        self.imm = Some((reg & 0xf) << 4);
+        self
+    }
+
+    /// Set the imm byte.
+    /// Overrides a previously set [Self::imm_reg] field.
+    #[inline(always)]
+    pub fn imm(mut self, imm: u8) -> Self {
+        self.imm = Some(imm);
+        self
+    }
+
+    /// The R bit in encoded format (inverted).
+    #[inline(always)]
+    fn r_bit(&self) -> u8 {
+        (!(self.reg >> 3)) & 1
+    }
+
+    /// The X bit in encoded format (inverted).
+    #[inline(always)]
+    fn x_bit(&self) -> u8 {
+        // TODO
+        (!0) & 1
+    }
+
+    /// The B bit in encoded format (inverted).
+    #[inline(always)]
+    fn b_bit(&self) -> u8 {
+        let rm: u8 = self.rm.into();
+        (!(rm >> 3)) & 1
+    }
+
+    /// Is the 2 byte prefix available for this instruction?
+    /// We essentially just check if we need any of the bits that are only available
+    /// in the 3 byte instruction
+    #[inline(always)]
+    fn use_2byte_prefix(&self) -> bool {
+        // These bits are only represented on the 3 byte prefix, so their presence
+        // implies the use of the 3 byte prefix
+        self.b_bit() == 1 && self.x_bit() == 1 &&
+        // The presence of W1 in the opcode column implies the opcode must be encoded using the
+        // 3-byte form of the VEX prefix.
+        self.w == false &&
+        // The presence of 0F3A and 0F38 in the opcode column implies that opcode can only be
+        // encoded by the three-byte form of VEX
+        !(self.map == OpcodeMap::_0F3A || self.map == OpcodeMap::_0F38)
+    }
+    /// The last byte of the 2byte and 3byte prefixes is mostly the same, share the common
+    /// encoding logic here.
+    #[inline(always)]
+    fn prefix_last_byte(&self) -> u8 {
+        let vvvv = self.vvvv.map(|r| r.into()).unwrap_or(0x00);
+
+        let mut byte = 0x00;
+        byte |= self.prefix.bits();
+        byte |= self.length.bits() << 2;
+        byte |= ((!vvvv) & 0xF) << 3;
+        byte
+    }
+
+    /// Encode the 2 byte prefix
+    #[inline(always)]
+    fn encode_2byte_prefix<CS: ByteSink + ?Sized>(&self, sink: &mut CS) {
+        //  2 bytes:
+        //    +-----+ +-------------------+
+        //    | C5h | | R | vvvv | L | pp |
+        //    +-----+ +-------------------+
+
+        let last_byte = self.prefix_last_byte() | (self.r_bit() << 7);
+
+        sink.put1(0xC5);
+        sink.put1(last_byte);
+    }
+
+    /// Encode the 3 byte prefix
+    #[inline(always)]
+    fn encode_3byte_prefix<CS: ByteSink + ?Sized>(&self, sink: &mut CS) {
+        //  3 bytes:
+        //    +-----+ +--------------+ +-------------------+
+        //    | C4h | | RXB | m-mmmm | | W | vvvv | L | pp |
+        //    +-----+ +--------------+ +-------------------+
+
+        let mut second_byte = 0x00;
+        second_byte |= self.map.bits(); // m-mmmm field
+        second_byte |= self.b_bit() << 5;
+        second_byte |= self.x_bit() << 6;
+        second_byte |= self.r_bit() << 7;
+
+        let w_bit = self.w as u8;
+        let last_byte = self.prefix_last_byte() | (w_bit << 7);
+
+        sink.put1(0xC4);
+        sink.put1(second_byte);
+        sink.put1(last_byte);
+    }
+
+    /// Emit the VEX-encoded instruction to the code sink:
+    pub fn encode<CS: ByteSink + ?Sized>(&self, sink: &mut CS) {
+        // 2/3 byte prefix
+        if self.use_2byte_prefix() {
+            self.encode_2byte_prefix(sink);
+        } else {
+            self.encode_3byte_prefix(sink);
+        }
+
+        // 1 Byte Opcode
+        sink.put1(self.opcode);
+
+        // 1 ModRM Byte
+        // Not all instructions use Reg as a reg, some use it as an extension of the opcode.
+        let rm: u8 = self.rm.into();
+        sink.put1(encode_modrm(3, self.reg & 7, rm & 7));
+
+        // TODO: 0/1 byte SIB
+        // TODO: 0/1/2/4 bytes DISP
+
+        // Optional 1 Byte imm
+        if let Some(imm) = self.imm {
+            sink.put1(imm);
+        }
+    }
+}
+
+/// The VEX format allows choosing a vector length in the `L` bit.
+#[allow(dead_code, missing_docs)] // Wider-length vectors are not yet used.
+pub enum VexVectorLength {
+    V128,
+    V256,
+}
+
+impl VexVectorLength {
+    /// Encode the `L` bit.
+    fn bits(&self) -> u8 {
+        match self {
+            Self::V128 => 0b0,
+            Self::V256 => 0b1,
+        }
+    }
+}
+
+impl Default for VexVectorLength {
+    fn default() -> Self {
+        Self::V128
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::isa::x64::inst::regs;
+    use std::vec::Vec;
+
+    #[test]
+    fn vpslldq() {
+        // VEX.128.66.0F 73 /7 ib
+        // VPSLLDQ xmm1, xmm2, imm8
+
+        let dst = regs::xmm1().to_real_reg().unwrap().hw_enc();
+        let src = regs::xmm2().to_real_reg().unwrap().hw_enc();
+        let mut sink0 = Vec::new();
+
+        VexInstruction::new()
+            .length(VexVectorLength::V128)
+            .prefix(LegacyPrefixes::_66)
+            .map(OpcodeMap::_0F)
+            .opcode(0x73)
+            .opcode_ext(7)
+            .vvvv(dst)
+            .rm(src)
+            .imm(0x17)
+            .encode(&mut sink0);
+
+        assert_eq!(sink0, vec![0xc5, 0xf1, 0x73, 0xfa, 0x17]);
+    }
+
+    #[test]
+    fn vblendvpd() {
+        // A four operand instruction
+        // VEX.128.66.0F3A.W0 4B /r /is4
+        // VBLENDVPD xmm1, xmm2, xmm3, xmm4
+
+        let dst = regs::xmm1().to_real_reg().unwrap().hw_enc();
+        let a = regs::xmm2().to_real_reg().unwrap().hw_enc();
+        let b = regs::xmm3().to_real_reg().unwrap().hw_enc();
+        let c = regs::xmm4().to_real_reg().unwrap().hw_enc();
+        let mut sink0 = Vec::new();
+
+        VexInstruction::new()
+            .length(VexVectorLength::V128)
+            .prefix(LegacyPrefixes::_66)
+            .map(OpcodeMap::_0F3A)
+            .w(false)
+            .opcode(0x4B)
+            .reg(dst)
+            .vvvv(a)
+            .rm(b)
+            .imm_reg(c)
+            .encode(&mut sink0);
+
+        assert_eq!(sink0, vec![0xc4, 0xe3, 0x69, 0x4b, 0xcb, 0x40]);
+    }
+
+    #[test]
+    fn vcmpps() {
+        // VEX.128.0F.WIG C2 /r ib
+        // VCMPPS ymm10, ymm11, ymm12, 4 // neq
+
+        let dst = regs::xmm10().to_real_reg().unwrap().hw_enc();
+        let a = regs::xmm11().to_real_reg().unwrap().hw_enc();
+        let b = regs::xmm12().to_real_reg().unwrap().hw_enc();
+        let mut sink0 = Vec::new();
+
+        VexInstruction::new()
+            .length(VexVectorLength::V256)
+            .prefix(LegacyPrefixes::None)
+            .map(OpcodeMap::_0F)
+            .opcode(0xC2)
+            .reg(dst)
+            .vvvv(a)
+            .rm(b)
+            .imm(4)
+            .encode(&mut sink0);
+
+        assert_eq!(sink0, vec![0xc4, 0x41, 0x24, 0xc2, 0xd4, 0x04]);
+    }
+}