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/inst.isle

@@ -193,6 +193,13 @@
                (src2 XmmMem)
                (dst WritableXmm))
 
+       ;; XMM (scalar or vector) binary op that relies on the VEX prefix.
+       (XmmRmRVex (op AvxOpcode)
+                   (src1 Xmm)
+                   (src2 Xmm)
+                   (src3 XmmMem)
+                   (dst WritableXmm))
+
        ;; XMM (scalar or vector) binary op that relies on the EVEX prefix.
        (XmmRmREvex (op Avx512Opcode)
                    (src1 XmmMem)
@@ -1042,6 +1049,10 @@
 (decl intcc_to_cc (IntCC) CC)
 (extern constructor intcc_to_cc intcc_to_cc)
 
+(type AvxOpcode extern
+      (enum Vfmadd213ps
+            Vfmadd213pd))
+
 (type Avx512Opcode extern
       (enum Vcvtudq2ps
             Vpabsq
@@ -2839,6 +2850,28 @@
         dst))
 
 
+;; Helper for creating `MInst.XmmRmRVex` instructions.
+(decl xmm_rmr_vex (AvxOpcode Xmm Xmm XmmMem) Xmm)
+(rule (xmm_rmr_vex op src1 src2 src3)
+      (let ((dst WritableXmm (temp_writable_xmm))
+            (_ Unit (emit (MInst.XmmRmRVex op
+                                           src1
+                                           src2
+                                           src3
+                                           dst))))
+        dst))
+
+;; Helper for creating `vfmadd213ps` instructions.
+(decl x64_vfmadd213ps (Xmm Xmm XmmMem) Xmm)
+(rule (x64_vfmadd213ps x y z)
+      (xmm_rmr_vex (AvxOpcode.Vfmadd213ps) x y z))
+
+;; Helper for creating `vfmadd213pd` instructions.
+(decl x64_vfmadd213pd (Xmm Xmm XmmMem) Xmm)
+(rule (x64_vfmadd213pd x y z)
+      (xmm_rmr_vex (AvxOpcode.Vfmadd213pd) x y z))
+
+
 ;; Helper for creating `sqrtss` instructions.
 (decl x64_sqrtss (Xmm) Xmm)
 (rule (x64_sqrtss x)