[WebAssembly] Update MC for bulk memory

Summary:
Rename MemoryIndex to InitFlags and implement logic for determining
data segment layout in ObjectYAML and MC. Also adds a "passive" flag
for the .section assembler directive although this cannot be assembled
yet because the assembler does not support data sections.

Reviewers: sbc100, aardappel, aheejin, dschuff

Subscribers: jgravelle-google, hiraditya, sunfish, rupprecht, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57938

llvm-svn: 354397

1 files changed, 12 insertions, 2 deletions

diff --git a/llvm/lib/ObjectYAML/WasmYAML.cpp b/llvm/lib/ObjectYAML/WasmYAML.cpp
index def4d58a101..1865dcf7aa6 100644
--- a/llvm/lib/ObjectYAML/WasmYAML.cpp
+++ b/llvm/lib/ObjectYAML/WasmYAML.cpp
@@ -403,8 +403,18 @@ void MappingTraits<wasm::WasmInitExpr>::mapping(IO &IO,
 void MappingTraits<WasmYAML::DataSegment>::mapping(
     IO &IO, WasmYAML::DataSegment &Segment) {
   IO.mapOptional("SectionOffset", Segment.SectionOffset);
-  IO.mapRequired("MemoryIndex", Segment.MemoryIndex);
-  IO.mapRequired("Offset", Segment.Offset);
+  IO.mapRequired("InitFlags", Segment.InitFlags);
+  if (Segment.InitFlags & wasm::WASM_SEGMENT_HAS_MEMINDEX) {
+    IO.mapRequired("MemoryIndex", Segment.MemoryIndex);
+  } else {
+    Segment.MemoryIndex = 0;
+  }
+  if ((Segment.InitFlags & wasm::WASM_SEGMENT_IS_PASSIVE) == 0) {
+    IO.mapRequired("Offset", Segment.Offset);
+  } else {
+    Segment.Offset.Opcode = wasm::WASM_OPCODE_I32_CONST;
+    Segment.Offset.Value.Int32 = 0;
+  }
   IO.mapRequired("Content", Segment.Content);
 }