[WebAssembly] Update format of 'names' section.

[sbc100]

Summary

This change updates to the format of the 'names' sectionin the
generated wasm binary to match the latest changesto the design
and 'wabt'.

[sbc100]

• Merge remote-tracking branch 'origin/master' into new_names_section

[sunfish]

Looks good!

lib/MC/WasmObjectWriter.cpp

994

Here and below, prefer preincrement.

[sbc100]

• prefer preincrement

include/llvm/Support/Wasm.h

enum : unsigned {
   WASM_OPCODE_END        = 0x0b,
   WASM_OPCODE_GET_GLOBAL = 0x23,
   WASM_OPCODE_I32_CONST  = 0x41,
   WASM_OPCODE_I64_CONST  = 0x42,
   WASM_OPCODE_F32_CONST  = 0x43,
   WASM_OPCODE_F64_CONST  = 0x44,
 };
 
+enum : unsigned {
+  WASM_NAMES_FUNCTION    = 0x1,
+  WASM_NAMES_LOCAL       = 0x2,
+};
+
 #define WASM_RELOC(name, value) name = value,
 
 enum : unsigned {
 #include "WasmRelocs/WebAssembly.def"
 };
 
 } // end namespace wasm
 } // end namespace llvm
 
 #endif

lib/MC/WasmObjectWriter.cpp

if (!DataBytes.empty()) {
     // Apply fixups.
     ApplyRelocations(DataRelocations, getStream(), SymbolIndices,
                      Section.ContentsOffset);
 
     endSection(Section);
   }
 
   // === Name Section ==========================================================
-  if (NumFuncImports != 0 || !Functions.empty()) {
+  uint32_t TotalFunctions = NumFuncImports + Functions.size();
+  if (TotalFunctions != 0) {
     startSection(Section, wasm::WASM_SEC_CUSTOM, "name");
+    SectionBookkeeping SubSection;
+    startSection(SubSection, wasm::WASM_NAMES_FUNCTION);
 
-    encodeULEB128(NumFuncImports + Functions.size(), getStream());
+    encodeULEB128(TotalFunctions, getStream());
+    uint32_t Index = 0;
     for (const WasmImport &Import : Imports) {
       if (Import.Kind == wasm::WASM_EXTERNAL_FUNCTION) {
+        encodeULEB128(Index, getStream());
         encodeULEB128(Import.FieldName.size(), getStream());
         writeBytes(Import.FieldName);
-        encodeULEB128(0, getStream()); // local count, meaningless for imports
+        Index++;
       }
     }
     for (const WasmFunction &Func : Functions) {
+      encodeULEB128(Index, getStream());
       encodeULEB128(Func.Sym->getName().size(), getStream());
       writeBytes(Func.Sym->getName());
-
-      // TODO: Local names.
-      encodeULEB128(0, getStream()); // local count
+      Index++;
     }
 
+    endSection(SubSection);
     endSection(Section);
   }
 
   // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
   // for descriptions of the reloc sections.
 
   // === Code Reloc Section ====================================================
   if (!CodeRelocations.empty()) {