test(asm): walk the loong64 audit backlog under every operand shape

Assisted-by: GLM 5.3 Flash

asm/loong64_errorparity_test.go

@@ -276,7 +276,8 @@ func TestLoong64PairErrorParity(t *testing.T) {
 // encode must be refused by gasm as well, and the one name the audit
 // misses because its probe battery lacks the shape (SCQ, whose only form
 // is the three-operand store-conditional) must encode to the toolchain's
-// own bytes.
+// own bytes.  The refusal claim is walked under the full operand-shape
+// battery below, against the live toolchain and against gasm alike.
 func TestLoong64BacklogNameParity(t *testing.T) {
 	if testing.Short() {
 		t.Skip("live toolchain backlog: skipped in -short mode")
@@ -286,6 +287,32 @@ func TestLoong64BacklogNameParity(t *testing.T) {
 			t.Errorf("gasm encodes %s, which the toolchain refuses under every shape", name)
 		}
 	}
+	// The shapes the plain audit probes, walked here so the backlog's
+	// claim holds under any operand shape, not only the bare mnemonic:
+	// the toolchain must refuse every combination, and gasm must refuse
+	// it too.
+	goroot := loong64Goroot(t)
+	for _, name := range loong64RejectedNames {
+		for _, shape := range loong64BacklogShapes {
+			body := strings.TrimSpace(name + " " + shape)
+			if loong64ProbeAssembles(body) {
+				t.Errorf("gasm encodes %s, which the toolchain refuses under every shape", body)
+			}
+			// The toolchain side of the same row: the file holds the one
+			// instruction, and the live assembler must report it.  A
+			// spelling the toolchain accepts would open the name for
+			// encoding and close nothing here but the parity.
+			src := "#include \"textflag.h\"\n\nTEXT ·f(SB), NOSPLIT, $0-0\np2:\n\t" + body + "\n\tRET\n"
+			dir := t.TempDir()
+			path := filepath.Join(dir, "backlogshape.s")
+			if err := os.WriteFile(path, []byte(src), 0o644); err != nil {
+				t.Fatalf("write: %v", err)
+			}
+			if lines := loong64ToolchainRejects(t, goroot, path); len(lines) == 0 {
+				t.Errorf("the toolchain assembles %q, against the backlog's claim", body)
+			}
+		}
+	}
 	// sc.q: loong64enc1.s pins the encoding as c4145738
 	// (SCQ R4, R5, (R6): sc.q rd, rk, (rj)).
 	src := "#include \"textflag.h\"\n\nTEXT ·f(SB), NOSPLIT, $0-0\n\tSCQ R4, R5, (R6)\n\tRET\n"
@@ -303,6 +330,18 @@ func TestLoong64BacklogNameParity(t *testing.T) {
 	}
 }
 
+// loong64BacklogShapes is the operand-shape battery the backlog walk runs
+// every rejected name through: the register, immediate, memory, vector and
+// label positions the loong64 grammar has, mirroring the plain audit's
+// probe battery (cmd/gasm's probeShapes) so the two answer the same
+// question.
+var loong64BacklogShapes = []string{
+	"", "R4", "R4, R5", "R4, R5, R6", "$1, R4", "R4, (R5)", "(R4), R5",
+	"F0, F1", "F0, F1, F2", "V1, V2", "X1, X2", "V1, FCC0", "$65536, R4",
+	"R4, R5, p2", "p2(SB)", "R5, (R4), R6", "$1, $0", "R1, R5, 0",
+	"0(R7), $5, $0", "V1, V2, V3, V4", "R4, R5, (R6)", "$16", "(R4)",
+}
+
 // loong64ProbeAssembles answers whether the single corpus line, wrapped in
 // its own function, parses and assembles on loong64.
 func loong64ProbeAssembles(body string) bool {