fix(asm): materialise RISC-V MOV immediates

asm/riscv_encode_test.go

@@ -122,7 +122,7 @@ done:
 }
 
 func TestRISCV_MOV_imm_small(t *testing.T) {
-	// MOV $42, rd → ADDI (fits in 12 bits). Not RVC-compressed (treated as MOV, not ADDI).
+	// MOV $42, rd → ADDI (fits in 12 bits, but not C.LI's 6-bit immediate).
 	fn := firstTextRISCV(t, `#include "textflag.h"
 TEXT ·small(SB), NOSPLIT, $0
 	MOV $42, X10
@@ -136,16 +136,16 @@ TEXT ·small(SB), NOSPLIT, $0
 }
 
 func TestRISCV_MOV_imm_large(t *testing.T) {
-	// MOV $0x12345, rd → LUI + ADDIW (8 bytes total)
+	// MOV $0x12345, rd → C.LUI $18 (2B) + ADDIW $837 (4B).
 	fn := firstTextRISCV(t, `#include "textflag.h"
 TEXT ·large(SB), NOSPLIT, $0
 	MOV $0x12345, X10
 	RET
 `)
 	code := assembleRISCVHelper(t, fn)
-	// LUI (4B) + ADDIW (4B) + JALR (4B) = 12
-	if len(code) != 12 {
-		t.Errorf("expected 12 bytes, got %d", len(code))
+	// C.LUI (2B) + ADDIW (4B) + JALR (4B) = 10
+	if len(code) != 10 {
+		t.Errorf("expected 10 bytes, got %d", len(code))
 	}
 }