feat(arch): add the imm8 scalar FP16 controls to the amd64 extension layer

Assisted-by: GLM 5.3 Flash

arch/arm64_ext.go

@@ -272,6 +272,16 @@ const (
 	// general-register destination: VMOVW EAX, X1 and VCVTSH2SI EAX, X1.
 	// Operands: src, dest.
 	ExtFormAmdVecGpr
+	// ExtFormAmdVec3Imm is the three-vector form with a control immediate,
+	// VGETMANTSH $11, X28, X29, X30 style: the immediate leads, the order
+	// the reference listings write it in.  Operands: imm, src1, src2, dest.
+	// The immediate's layout is named by the entry's Imm8 kind.
+	ExtFormAmdVec3Imm
+	// ExtFormAmdMask2Imm is the opmask-destination form with a control
+	// immediate: VCMPSH $7, X28, X29, K5.  Operands: imm, src1, src2, dest,
+	// where dest is an opmask register and the immediate's layout is named
+	// by the entry's Imm8 kind.
+	ExtFormAmdMask2Imm
 )
 
 // Arity returns the operand count the form takes.
@@ -285,6 +295,8 @@ func (f ExtForm) Arity() int {
 		return 3
 	case ExtFormAmdVec2, ExtFormAmdVec2Half, ExtFormAmdGprVec, ExtFormAmdVecGpr:
 		return 2
+	case ExtFormAmdVec3Imm, ExtFormAmdMask2Imm:
+		return 4
 	default:
 		return 0
 	}
@@ -334,6 +346,10 @@ func (f ExtForm) String() string {
 		return "general register, vector"
 	case ExtFormAmdVecGpr:
 		return "vector, general register"
+	case ExtFormAmdVec3Imm:
+		return "immediate, three vectors"
+	case ExtFormAmdMask2Imm:
+		return "immediate, two vectors into an opmask"
 	default:
 		return "unknown form"
 	}
@@ -350,6 +366,45 @@ const (
 	ExtFeatureSVE2 ExtFeature = "sve2"
 )
 
+// ExtImm8Kind names the imm8-control layout an amd64 extended entry carries
+// in its immediate operand.  The kind drives the validation at encode time:
+// a value the manual reserves is an error, never a silent mis-encoding.
+type ExtImm8Kind uint8
+
+// The imm8-control layouts, ExtImm8None first as the zero value an entry
+// without an immediate carries.
+const (
+	// ExtImm8None marks a form that takes no immediate operand.
+	ExtImm8None ExtImm8Kind = iota
+	// ExtImm8ScaleRound is the fraction-bits-plus-round-control layout of
+	// VRNDSCALESH and VREDUCESH: imm8[7:4] carries the number of fraction
+	// bits M, imm8[3] the precision-exception control, imm8[2] the rounding
+	// mode source and imm8[1:0] the rounding mode.  Every byte encodes.
+	ExtImm8ScaleRound
+	// ExtImm8GetMant is the mantissa-extraction control of VGETMANTSH:
+	// imm8[3:2] the sign control, imm8[1:0] the normalisation interval,
+	// and imm8[7:4] reserved, which must encode as zero.
+	ExtImm8GetMant
+	// ExtImm8CmpPredicate is the comparison-predicate control of VCMPSH:
+	// imm8[4:0] names one of the 32 predicates and the bits above are
+	// masked away by the hardware, so every byte encodes.
+	ExtImm8CmpPredicate
+)
+
+// String returns a short label for the imm8-control layout, for diagnostics.
+func (k ExtImm8Kind) String() string {
+	switch k {
+	case ExtImm8ScaleRound:
+		return "fraction bits and round control"
+	case ExtImm8GetMant:
+		return "mantissa extraction control"
+	case ExtImm8CmpPredicate:
+		return "comparison predicate"
+	default:
+		return "no immediate"
+	}
+}
+
 // ExtInstr is one extended instruction: the metadata a lookup needs and the
 // encoding as data.  Word holds the fixed bits of the 32-bit encoding with
 // every operand field and the size field zero; the form says which fields the
@@ -372,6 +427,10 @@ type ExtInstr struct {
 	// Wig records that the entry ignores the W bit in its general-register
 	// position, so both 32-bit and 64-bit registers encode.
 	Wig bool
+	// Imm8 names the imm8-control layout the amd64 entry's immediate
+	// operand carries, ExtImm8None when the form takes none.  The arm64
+	// entries all carry the zero value.
+	Imm8 ExtImm8Kind
 }
 
 // Encode assembles the operands into the 4 little-endian bytes of the
@@ -393,7 +452,8 @@ func (in ExtInstr) Encode(ops []ExtOperand) ([]byte, error) {
 	case ExtFormSignedImmediate:
 		return in.encodeSignedImmediate(ops)
 	case ExtFormAmdVec3, ExtFormAmdVec2, ExtFormAmdVec2Half, ExtFormAmdMask2,
-		ExtFormAmdVecGprVec, ExtFormAmdGprVec, ExtFormAmdVecGpr:
+		ExtFormAmdVecGprVec, ExtFormAmdGprVec, ExtFormAmdVecGpr,
+		ExtFormAmdVec3Imm, ExtFormAmdMask2Imm:
 		return in.encodeAmd64(ops)
 	default:
 		return nil, fmt.Errorf("%s: unknown form %d", in.Name, in.Form)