Use Names instead of indices to identify segments (#5618)

All top-level Module elements are identified and referred to by Name, but for
historical reasons element and data segments were referred to by index instead.
Fix this inconsistency by using Names to refer to segments from expressions that
use them. Also parse and print segment names like we do for other elements.

The C API is partially converted to use names instead of indices, but there are
still many functions that refer to data segments by index. Finishing the
conversion can be done in the future once it becomes necessary.

1 files changed, 23 insertions, 7 deletions

diff --git a/src/wasm2js.h b/src/wasm2js.h
index 054f442dc..c86788e5a 100644
--- a/src/wasm2js.h
+++ b/src/wasm2js.h
@@ -168,6 +168,9 @@ public:
     std::string symbolsFile;
   };
 
+  // Map data segment names to indices.
+  std::unordered_map<Name, Index> dataIndices;
+
   Wasm2JSBuilder(Flags f, PassOptions options_) : flags(f), options(options_) {
     // We don't try to model wasm's trapping precisely - if we did, each load
     // and store would need to do a check. Given that, we can just ignore
@@ -191,6 +194,12 @@ public:
   // JS
   Ref processFunctionBody(Module* m, Function* func, bool standalone);
 
+  Index getDataIndex(Name segment) {
+    auto it = dataIndices.find(segment);
+    assert(it != dataIndices.end());
+    return it->second;
+  }
+
   // Get a temp var.
   IString getTemp(Type type, Function* func) {
     IString ret;
@@ -333,6 +342,11 @@ Ref Wasm2JSBuilder::processWasm(Module* wasm, Name funcName) {
   ElementUtils::iterAllElementFunctionNames(
     wasm, [&](Name name) { functionsCallableFromOutside.insert(name); });
 
+  // Collect passive data segment indices.
+  for (Index i = 0; i < wasm->dataSegments.size(); ++i) {
+    dataIndices[wasm->dataSegments[i]->name] = i;
+  }
+
   // Ensure the scratch memory helpers.
   // If later on they aren't needed, we'll clean them up.
   ABI::wasm2js::ensureHelpers(wasm);
@@ -2178,16 +2192,18 @@ Ref Wasm2JSBuilder::processFunctionBody(Module* m,
     }
     Ref visitMemoryInit(MemoryInit* curr) {
       ABI::wasm2js::ensureHelpers(module, ABI::wasm2js::MEMORY_INIT);
-      return ValueBuilder::makeCall(ABI::wasm2js::MEMORY_INIT,
-                                    ValueBuilder::makeNum(curr->segment),
-                                    visit(curr->dest, EXPRESSION_RESULT),
-                                    visit(curr->offset, EXPRESSION_RESULT),
-                                    visit(curr->size, EXPRESSION_RESULT));
+      return ValueBuilder::makeCall(
+        ABI::wasm2js::MEMORY_INIT,
+        ValueBuilder::makeNum(parent->getDataIndex(curr->segment)),
+        visit(curr->dest, EXPRESSION_RESULT),
+        visit(curr->offset, EXPRESSION_RESULT),
+        visit(curr->size, EXPRESSION_RESULT));
     }
     Ref visitDataDrop(DataDrop* curr) {
       ABI::wasm2js::ensureHelpers(module, ABI::wasm2js::DATA_DROP);
-      return ValueBuilder::makeCall(ABI::wasm2js::DATA_DROP,
-                                    ValueBuilder::makeNum(curr->segment));
+      return ValueBuilder::makeCall(
+        ABI::wasm2js::DATA_DROP,
+        ValueBuilder::makeNum(parent->getDataIndex(curr->segment)));
     }
     Ref visitMemoryCopy(MemoryCopy* curr) {
       ABI::wasm2js::ensureHelpers(module, ABI::wasm2js::MEMORY_COPY);