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/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