[WebAssembly] Add COMDAT support

This adds COMDAT support to the Wasm object-file format.
Spec: https://github.com/WebAssembly/tool-conventions/pull/31

Corresponding LLD change:
https://bugs.llvm.org/show_bug.cgi?id=35533, and D40845

Patch by Nicholas Wilson

Differential Revision: https://reviews.llvm.org/D40844

llvm-svn: 322135

1 files changed, 17 insertions, 0 deletions

diff --git a/llvm/tools/yaml2obj/yaml2wasm.cpp b/llvm/tools/yaml2obj/yaml2wasm.cpp
index 7770622149c..5c3b2b996ba 100644
--- a/llvm/tools/yaml2obj/yaml2wasm.cpp
+++ b/llvm/tools/yaml2obj/yaml2wasm.cpp
@@ -175,6 +175,23 @@ int WasmWriter::writeSectionContent(raw_ostream &OS, WasmYAML::LinkingSection &S
     }
     SubSection.Done();
   }
+
+  // COMDAT_INFO subsection
+  if (Section.Comdats.size()) {
+    encodeULEB128(wasm::WASM_COMDAT_INFO, OS);
+    encodeULEB128(Section.Comdats.size(), SubSection.GetStream());
+    for (const auto &C : Section.Comdats) {
+      writeStringRef(C.Name, SubSection.GetStream());
+      encodeULEB128(0, SubSection.GetStream()); // flags for future use
+      encodeULEB128(C.Entries.size(), SubSection.GetStream());
+      for (const WasmYAML::ComdatEntry &Entry : C.Entries) {
+        encodeULEB128(Entry.Kind, SubSection.GetStream());
+        encodeULEB128(Entry.Index, SubSection.GetStream());
+      }
+    }
+    SubSection.Done();
+  }
+
   return 0;
 }