x64: Add rudimentary support for some AVX instructions

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

@@ -312,18 +312,50 @@ pub(crate) fn emit_std_enc_mem(
 
     prefixes.emit(sink);
 
+    // After prefixes, first emit the REX byte depending on the kind of
+    // addressing mode that's being used.
     match *mem_e {
-        Amode::ImmReg { simm32, base, .. } => {
-            // First, the REX byte.
+        Amode::ImmReg { base, .. } => {
             let enc_e = int_reg_enc(base);
             rex.emit_two_op(sink, enc_g, enc_e);
+        }
 
-            // Now the opcode(s).  These include any other prefixes the caller
-            // hands to us.
-            while num_opcodes > 0 {
-                num_opcodes -= 1;
-                sink.put1(((opcodes >> (num_opcodes << 3)) & 0xFF) as u8);
-            }
+        Amode::ImmRegRegShift {
+            base: reg_base,
+            index: reg_index,
+            ..
+        } => {
+            let enc_base = int_reg_enc(*reg_base);
+            let enc_index = int_reg_enc(*reg_index);
+            rex.emit_three_op(sink, enc_g, enc_index, enc_base);
+        }
+
+        Amode::RipRelative { .. } => {
+            // note REX.B = 0.
+            rex.emit_two_op(sink, enc_g, 0);
+        }
+    }
+
+    // Now the opcode(s).  These include any other prefixes the caller
+    // hands to us.
+    while num_opcodes > 0 {
+        num_opcodes -= 1;
+        sink.put1(((opcodes >> (num_opcodes << 3)) & 0xFF) as u8);
+    }
+
+    // And finally encode the mod/rm bytes and all further information.
+    emit_modrm_sib_disp(sink, enc_g, mem_e, bytes_at_end)
+}
+
+pub(crate) fn emit_modrm_sib_disp(
+    sink: &mut MachBuffer<Inst>,
+    enc_g: u8,
+    mem_e: &Amode,
+    bytes_at_end: u8,
+) {
+    match *mem_e {
+        Amode::ImmReg { simm32, base, .. } => {
+            let enc_e = int_reg_enc(base);
 
             // Now the mod/rm and associated immediates.  This is
             // significantly complicated due to the multiple special cases.
@@ -377,15 +409,6 @@ pub(crate) fn emit_std_enc_mem(
             let enc_base = int_reg_enc(*reg_base);
             let enc_index = int_reg_enc(*reg_index);
 
-            // The rex byte.
-            rex.emit_three_op(sink, enc_g, enc_index, enc_base);
-
-            // All other prefixes and opcodes.
-            while num_opcodes > 0 {
-                num_opcodes -= 1;
-                sink.put1(((opcodes >> (num_opcodes << 3)) & 0xFF) as u8);
-            }
-
             // modrm, SIB, immediates.
             if low8_will_sign_extend_to_32(simm32) && enc_index != regs::ENC_RSP {
                 sink.put1(encode_modrm(1, enc_g & 7, 4));
@@ -401,16 +424,6 @@ pub(crate) fn emit_std_enc_mem(
         }
 
         Amode::RipRelative { ref target } => {
-            // First, the REX byte, with REX.B = 0.
-            rex.emit_two_op(sink, enc_g, 0);
-
-            // Now the opcode(s).  These include any other prefixes the caller
-            // hands to us.
-            while num_opcodes > 0 {
-                num_opcodes -= 1;
-                sink.put1(((opcodes >> (num_opcodes << 3)) & 0xFF) as u8);
-            }
-
             // RIP-relative is mod=00, rm=101.
             sink.put1(encode_modrm(0, enc_g & 7, 0b101));