fix(asm): encode the CMOV condition the renderer prints

The renderer spells a conditional move CMOV plus the condition alone
(CMOVLE, CMOVG), the width carried by the operand registers, so
CMOVLE parsed as the size L and the condition E and encoded CMOVE.
A suffix that is itself a condition name now reads as that condition
with the width from the destination register, and the Plan 9
size-prefixed spellings keep their parse.

Assisted-by: GLM 5.3 Flash

asm/encodable.go

@@ -62,16 +62,14 @@ func Encodable(mnemonic string) bool {
 		return true
 	}
 
-	// CMOV carries size then condition (CMOVLGT); SET carries the condition
-	// alone (SETNE).  The size letter is checked exactly as encodeCmov does,
-	// so a spelling like CMOVBGT is not reported encodable when Encode
-	// would reject it.
-	if rest, ok := strings.CutPrefix(upper, "CMOV"); ok && len(rest) >= 2 {
-		switch rest[0] {
-		case 'W', 'L', 'Q':
-			if _, ok := jccMap[rest[1:]]; ok {
-				return true
-			}
+	// CMOV carries size then condition (CMOVLGT), or the renderer's
+	// condition alone (CMOVLE) with the width from the operand; SET carries
+	// the condition alone (SETNE).  cmovCondition checks the suffix exactly
+	// as encodeCmov does, so a spelling like CMOVBGT is not reported
+	// encodable when Encode would reject it.
+	if rest, ok := strings.CutPrefix(upper, "CMOV"); ok {
+		if _, _, ok := cmovCondition(rest); ok {
+			return true
 		}
 	}
 	if rest, ok := strings.CutPrefix(upper, "SET"); ok {

asm/encode_test.go

@@ -411,6 +411,16 @@ func TestScalarGroundTruth(t *testing.T) {
 		{"CMOVLEQ CX,AX", "CMOVLEQ", []Operand{CX, AX}, "0f44c1", "CMOVE"},
 		{"CMOVQGT R9,R8", "CMOVQGT", []Operand{r9, r8}, "4d0f4fc1", "CMOVG"},
 		{"CMOVWLS R9W,R8W", "CMOVWLS", []Operand{r9w, r8w}, "66450f46c1", "CMOVBE"},
+		// The renderer's condition spellings carry no size letter; the width
+		// rides the operand registers and the bytes match the toolchain's own
+		// size-prefixed spellings (CMOVQLE/CMOVLLE/CMOVWLE pinned from go tool
+		// asm).  CMOVLE with the 16-bit registers reproduces the disasm
+		// fixture's 660f4e13 row byte for byte.
+		{"CMOVLE (BX),DX", "CMOVLE", []Operand{Ptr(BX, 0, 2), DX}, "660f4e13", "CMOVLE"},
+		{"CMOVQLE AX,BX", "CMOVQLE", []Operand{Reg{idx: 0, size: 8}, Reg{idx: 3, size: 8}}, "480f4ed8", "CMOVLE"},
+		{"CMOVLLE AX,BX", "CMOVLLE", []Operand{Reg{idx: 0, size: 4}, Reg{idx: 3, size: 4}}, "0f4ed8", "CMOVLE"},
+		{"CMOVWLE AX,BX", "CMOVWLE", []Operand{AX, BX}, "660f4ed8", "CMOVLE"},
+		{"CMOVB AL,CL", "CMOVB", []Operand{AL, CL}, "0f42c8", "CMOVB"},
 		{"SETNE AL", "SETNE", []Operand{AL}, "0f95c0", "SETNE"},
 		{"SETNE (AX)", "SETNE", []Operand{Ptr(AX, 0, 1)}, "0f9500", "SETNE"},
 		{"MOVBLZX AL,CX", "MOVBLZX", []Operand{AL, CX}, "0fb6c8", "MOVZX"},
@@ -595,14 +605,15 @@ func TestImmediateTruncation(t *testing.T) {
 
 // TestEncodableCmovSize pins the linter contract for CMOVcc: Encodable must
 // reject the spellings Encode rejects, so a mnemonic like CMOVBGT (no size
-// letter) is not reported as encodable.
+// letter) is not reported as encodable.  The condition-name spellings the
+// renderer prints (CMOVB, CMOVLE) encode with the width from the operands.
 func TestEncodableCmovSize(t *testing.T) {
-	for _, m := range []string{"CMOVBGT", "CMOVXEQ", "CMOVB", "CMOV", "CMOVWXX"} {
+	for _, m := range []string{"CMOVBGT", "CMOVXEQ", "CMOV", "CMOVWXX"} {
 		if Encodable(m) {
 			t.Errorf("Encodable(%q) = true, want false", m)
 		}
 	}
-	for _, m := range []string{"CMOVLGT", "CMOVQGT", "CMOVWLS", "CMOVLEQ"} {
+	for _, m := range []string{"CMOVLGT", "CMOVQGT", "CMOVWLS", "CMOVLEQ", "CMOVB", "CMOVLE"} {
 		if !Encodable(m) {
 			t.Errorf("Encodable(%q) = false, want true", m)
 		}

asm/instrs.go

@@ -1068,29 +1068,46 @@ func immediate(v int64, size int, full64 bool) ([]byte, error) {
 
 // --- CMOVcc / SETcc ---------------------------------------------------------
 
+// cmovCondition splits a CMOVcc suffix into an optional size letter and the
+// condition code.  Two vocabularies meet here: the Plan 9 spellings prefix
+// the condition with a size letter (CMOVLGT, CMOVQEQ), while the toolchain's
+// renderer prints the condition alone (CMOVLE, CMOVG) and leaves the width
+// to the operand registers.  A suffix that is itself a condition name reads
+// as that condition, so the renderer's text re-encodes; CMOVBGT, CMOVWXX and
+// the bare CMOV still find no condition and stay rejected.
+func cmovCondition(rest string) (size int, cc int, ok bool) {
+	if cc, ok := jccMap[rest]; ok {
+		return 0, cc, true
+	}
+	if len(rest) >= 2 {
+		switch rest[0] {
+		case 'W':
+			if cc, ok := jccMap[rest[1:]]; ok {
+				return 2, cc, true
+			}
+		case 'L':
+			if cc, ok := jccMap[rest[1:]]; ok {
+				return 4, cc, true
+			}
+		case 'Q':
+			if cc, ok := jccMap[rest[1:]]; ok {
+				return 8, cc, true
+			}
+		}
+	}
+	return 0, 0, false
+}
+
 // encodeCmov encodes a conditional move: CMOV + size (W/L/Q) + condition
-// (CMOVLGT, CMOVQEQ, …).  The condition reads exactly like the Jcc spellings;
-// the instruction is 0F 40+cc with reg = dst, rm = src.
+// (CMOVLGT, CMOVQEQ, …), or the renderer's condition alone (CMOVLE) with the
+// width taken from the destination register.  The instruction is 0F 40+cc
+// with reg = dst, rm = src.
 func (e *enc) encodeCmov(upper string, ops []Operand) error {
 	if len(ops) != 2 {
 		return fmt.Errorf("CMOVcc expects 2 operands, got %d", len(ops))
 	}
 	rest := upper[len("CMOV"):]
-	if len(rest) < 2 {
-		return fmt.Errorf("unsupported instruction %q", upper)
-	}
-	var size int
-	switch rest[0] {
-	case 'W':
-		size = 2
-	case 'L':
-		size = 4
-	case 'Q':
-		size = 8
-	default:
-		return fmt.Errorf("unsupported instruction %q", upper)
-	}
-	cc, ok := jccMap[rest[1:]]
+	size, cc, ok := cmovCondition(rest)
 	if !ok {
 		return fmt.Errorf("unsupported instruction %q", upper)
 	}
@@ -1099,6 +1116,14 @@ func (e *enc) encodeCmov(upper string, ops []Operand) error {
 	if !ok {
 		return fmt.Errorf("CMOVcc destination must be a register")
 	}
+	if size == 0 {
+		// The renderer's spelling carries no size letter: the width rides
+		// the destination register's own size class.
+		size = dstReg.size
+		if size != 1 && size != 2 && size != 4 && size != 8 {
+			return fmt.Errorf("CMOVcc destination must be a general register")
+		}
+	}
 	i := newInstr(size, []byte{0x0F, byte(0x40 + cc)})
 	if err := setRM(i, dstReg, src, size); err != nil {
 		return err