diff --git a/core/rexcode/ir/spirv/tests/roundtrip_test.odin b/core/rexcode/ir/spirv/tests/roundtrip_test.odin
new file mode 100644
index 000000000..b937e6942
--- /dev/null
+++ b/core/rexcode/ir/spirv/tests/roundtrip_test.odin
@@ -0,0 +1,130 @@
+// rexcode  ·  Brendan Punsky (dotbmp@github), original author
+
+// SPIR-V codec round-trip suite. For each module shape: encode -> decode ->
+// re-encode and assert the two encodings are byte-identical. A byte-exact
+// round-trip exercises the encoder, the decoder, the <id> side tables, and the
+// generic table-driven operation codec all at once: any drift in operand order,
+// id mapping, or section layout shows up as a word mismatch.
+package rexcode_spirv_tests
+
+import "core:fmt"
+import "core:os"
+import "core:slice"
+import spirv ".."
+
+ok_count:   int
+fail_count: int
+
+@(private="file")
+roundtrip :: proc(name: string, m: spirv.Module) {
+	buf1 := make([]u8, 64 * 1024, context.temp_allocator)
+	buf2 := make([]u8, 64 * 1024, context.temp_allocator)
+	relocs: [dynamic]spirv.Relocation; defer delete(relocs)
+	errors: [dynamic]spirv.Error;      defer delete(errors)
+
+	n1, ok1 := spirv.encode(m, buf1, &relocs, &errors)
+	if !ok1 {
+		fmt.printf("  [FAIL] %s: encode failed\n", name); fail_count += 1; return
+	}
+
+	m2: spirv.Module
+	derr: [dynamic]spirv.Error; defer delete(derr)
+	_, ok2 := spirv.decode(buf1[:n1], &m2, &derr, context.temp_allocator)
+	if !ok2 {
+		fmt.printf("  [FAIL] %s: decode failed\n", name); fail_count += 1; return
+	}
+
+	n2, ok3 := spirv.encode(m2, buf2, &relocs, &errors)
+	if !ok3 {
+		fmt.printf("  [FAIL] %s: re-encode failed\n", name); fail_count += 1; return
+	}
+
+	if n1 != n2 || !slice.equal(buf1[:n1], buf2[:n2]) {
+		fmt.printf("  [FAIL] %s: round-trip mismatch (n1=%d n2=%d)\n", name, n1, n2)
+		for i := u32(0); i < max(n1, n2); i += 4 {
+			w1 := i < n1 ? word_at(buf1, i) : 0
+			w2 := i < n2 ? word_at(buf2, i) : 0
+			if w1 != w2 { fmt.printf("           [%d] %08x != %08x\n", i / 4, w1, w2) }
+		}
+		fail_count += 1
+		return
+	}
+	fmt.printf("  [ok]   %-22s %d bytes\n", name, n1)
+	ok_count += 1
+}
+
+@(private="file")
+word_at :: proc(b: []u8, i: u32) -> u32 {
+	return u32(b[i]) | u32(b[i + 1]) << 8 | u32(b[i + 2]) << 16 | u32(b[i + 3]) << 24
+}
+
+main :: proc() {
+	fmt.println("==== SPIR-V codec round-trip ====")
+
+	// (1) a void compute entry point: header + preamble + a void function.
+	{
+		m := spirv.make_module()
+		m.capabilities = {.Shader}
+		m.entry_points = {{model = .GLCompute, function = spirv.Id(4), name = "main"}}
+		m.types = {
+			{kind = .VOID},
+			{kind = .FUNCTION, fields = {spirv.Type_Ref(0)}, count = 0},
+		}
+		m.type_ids = {spirv.Id(2), spirv.Id(3)}
+		m.functions = {
+			{signature = spirv.Type_Ref(1), blocks = {
+				{id = spirv.Id(5), ops = {{opcode = u16(spirv.Opcode.OpReturn)}}},
+			}},
+		}
+		m.function_ids = {spirv.Id(4)}
+		m.bound = 6
+		roundtrip("void_main", m)
+	}
+
+	// (2) an int type + two scalar constants (the constant pool + OpConstant width).
+	{
+		m := spirv.make_module()
+		m.capabilities = {.Shader}
+		m.types = {{kind = .INT, bits = 32, aux = 1}}   // signed i32
+		m.type_ids = {spirv.Id(1)}
+		m.constants = {
+			{result = {spirv.Id(2), spirv.Type_Ref(0)}, opcode = .OpConstant, value = 10},
+			{result = {spirv.Id(3), spirv.Type_Ref(0)}, opcode = .OpConstant, value = 0xDEAD_BEEF},
+		}
+		m.bound = 4
+		roundtrip("int_constants", m)
+	}
+
+	// (3) a function body with a real operation (the generic operand codec):
+	//     %6 = OpIAdd %i32 %const_a %const_b ; OpReturn
+	{
+		m := spirv.make_module()
+		m.capabilities = {.Shader}
+		m.types = {
+			{kind = .VOID},
+			{kind = .INT, bits = 32, aux = 1},
+			{kind = .FUNCTION, fields = {spirv.Type_Ref(0)}, count = 0},
+		}
+		m.type_ids = {spirv.Id(1), spirv.Id(2), spirv.Id(3)}
+		m.constants = {
+			{result = {spirv.Id(4), spirv.Type_Ref(1)}, opcode = .OpConstant, value = 10},
+			{result = {spirv.Id(5), spirv.Type_Ref(1)}, opcode = .OpConstant, value = 20},
+		}
+		add := spirv.Operation{
+			opcode   = u16(spirv.Opcode.OpIAdd),
+			result   = {spirv.Id(6), spirv.Type_Ref(1)},
+			operands = {spirv.op_value(spirv.Id(4)), spirv.op_value(spirv.Id(5))},
+		}
+		m.functions = {
+			{signature = spirv.Type_Ref(2), blocks = {
+				{id = spirv.Id(8), ops = {add, {opcode = u16(spirv.Opcode.OpReturn)}}},
+			}},
+		}
+		m.function_ids = {spirv.Id(7)}
+		m.bound = 9
+		roundtrip("iadd_function", m)
+	}
+
+	fmt.printf("\n%d passed, %d failed\n", ok_count, fail_count)
+	if fail_count > 0 { os.exit(1) }
+}