Fix DataSegment name handling

src/wasm/wasm-binary.cpp

@@ -3700,7 +3700,7 @@ void WasmBinaryReader::readNames(size_t payloadLen) {
         auto rawName = getInlineString();
         auto name = processor.process(rawName);
         if (index < wasm.dataSegments.size()) {
-          wasm.dataSegments[i]->setExplicitName(name);
+          wasm.dataSegments[index]->setExplicitName(name);
         } else {
           std::cerr << "warning: data index out of bounds in name section, "
                        "data subsection: "

test/lit/binary/data-names.test

@@ -0,0 +1,25 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+;; RUN: wasm-opt -all %s.wasm -q -S -o - | filecheck %s
+
+;; Test that data segment names roundtrip properly. The wasm file contains
+;;
+;; (module
+;;   (memory $mem 10)
+;;   (data $passive1 "passive1")
+;;   (data $passive2 "passive2")
+;;   (data $active1 (offset i32.const 0) "active1")
+;;   (data $active2 (offset i32.const 0) "active2")
+;; )
+;;
+;; But the names section is *reversed*: the name of the last data segment is
+;; first, and so forth. We must still give the proper segments their names.
+
+;; CHECK:      (memory $mem 10)
+
+;; CHECK:      (data $passive1 "passive1")
+
+;; CHECK:      (data $passive2 "passive2")
+
+;; CHECK:      (data $active1 (i32.const 0) "active1")
+
+;; CHECK:      (data $active2 (i32.const 0) "active2")