feat(asm): take the loong64 register-pair spellings the toolchain parses

Assisted-by: GLM 5.3 Flash

asm/loong64_encode_test.go

@@ -1058,3 +1058,50 @@ TEXT ·bytes(SB), NOSPLIT, $0
 		}
 	}
 }
+
+// TestLOONG64PairSugar pins the toolchain's register-pair spellings: a
+// top-level colon between two registers splits the operand in two with the
+// halves swapped, so INSTR R4:R5, R6 encodes exactly as INSTR R5, R4, R6.
+// Each row is pinned two ways: against the word GOARCH=loong64 go tool asm
+// emits for the pair spelling, and against gasm's own encoding of the
+// direct spelling, which must be the same bytes.
+func TestLOONG64PairSugar(t *testing.T) {
+	for _, tt := range []struct {
+		pair, direct string
+		want         uint32 // the word go tool asm emits for the pair
+	}{
+		{"MULV R4:R5, R6", "MULV R5, R4, R6", 0x001D9486},
+		{"MULV R4:R5", "MULV R5, R4", 0x001D9484},
+		{"MULV R6, R4:R5", "MULV R6, R5, R4", 0x001D98A4},
+		{"DIVV R4:R5, R6", "DIVV R5, R4, R6", 0x00221486},
+		{"MULHV R4:R5, R6", "MULHV R5, R4, R6", 0x001E1486},
+		{"ADDV R4:R5, R6", "ADDV R5, R4, R6", 0x00109486},
+		{"AND R4:R5, R6", "AND R5, R4, R6", 0x00149486},
+		{"MOVV R4:R5", "MOVV R5, R4", 0x001500A4},
+		{"MULD F4:F5, F6", "MULD F5, F4, F6", 0x01051486},
+		{"VADDW V1:V2, V3", "VADDW V2, V1, V3", 0x700B0823},
+	} {
+		t.Run(tt.pair, func(t *testing.T) {
+			pair := assembleLOONG64Helper(t, firstTextLOONG64(t, `#include "textflag.h"
+TEXT ·p(SB), NOSPLIT, $0
+	`+tt.pair+`
+	RET
+`))
+			direct := assembleLOONG64Helper(t, firstTextLOONG64(t, `#include "textflag.h"
+TEXT ·d(SB), NOSPLIT, $0
+	`+tt.direct+`
+	RET
+`))
+			if len(pair) < 4 {
+				t.Fatalf("pair spelling produced %d bytes", len(pair))
+			}
+			got := binary.LittleEndian.Uint32(pair)
+			if got != tt.want {
+				t.Errorf("pair word = %08x, want %08x (go tool asm)", got, tt.want)
+			}
+			if len(direct) < 4 || !bytes.Equal(pair[:4], direct[:4]) {
+				t.Errorf("pair bytes % x differ from the direct spelling's % x", pair[:4], direct[:4])
+			}
+		})
+	}
+}