[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

3 files changed, 22 insertions, 4 deletions

diff --git a/llvm/include/llvm/BinaryFormat/Wasm.h b/llvm/include/llvm/BinaryFormat/Wasm.h
index 51f6ab2594b..7848be1cbfa 100644
--- a/llvm/include/llvm/BinaryFormat/Wasm.h
+++ b/llvm/include/llvm/BinaryFormat/Wasm.h
@@ -131,12 +131,13 @@ struct WasmFunction {
 };
 
 struct WasmDataSegment {
-  uint32_t MemoryIndex;
-  WasmInitExpr Offset;
+  uint32_t InitFlags;
+  uint32_t MemoryIndex; // present if InitFlags & WASM_SEGMENT_HAS_MEMINDEX
+  WasmInitExpr Offset; // present if InitFlags & WASM_SEGMENT_IS_PASSIVE == 0
   ArrayRef<uint8_t> Content;
   StringRef Name; // from the "segment info" section
   uint32_t Alignment;
-  uint32_t Flags;
+  uint32_t LinkerFlags;
   uint32_t Comdat; // from the "comdat info" section
 };
 
@@ -247,6 +248,11 @@ enum : unsigned {
   WASM_LIMITS_FLAG_IS_SHARED = 0x2,
 };
 
+enum : unsigned {
+  WASM_SEGMENT_IS_PASSIVE = 0x01,
+  WASM_SEGMENT_HAS_MEMINDEX = 0x02,
+};
+
 // Kind codes used in the custom "name" section
 enum : unsigned {
   WASM_NAMES_FUNCTION = 0x1,
diff --git a/llvm/include/llvm/MC/MCSectionWasm.h b/llvm/include/llvm/MC/MCSectionWasm.h
index 0e576b7ba40..1adc8126492 100644
--- a/llvm/include/llvm/MC/MCSectionWasm.h
+++ b/llvm/include/llvm/MC/MCSectionWasm.h
@@ -42,6 +42,9 @@ class MCSectionWasm final : public MCSection {
   // segment
   uint32_t SegmentIndex = 0;
 
+  // Whether this data segment is passive
+  bool IsPassive = false;
+
   friend class MCContext;
   MCSectionWasm(StringRef Section, SectionKind K, const MCSymbolWasm *group,
                 unsigned UniqueID, MCSymbol *Begin)
@@ -75,6 +78,14 @@ public:
   uint32_t getSegmentIndex() const { return SegmentIndex; }
   void setSegmentIndex(uint32_t Index) { SegmentIndex = Index; }
 
+  bool getPassive() const {
+    assert(isWasmData());
+    return IsPassive;
+  }
+  void setPassive(bool V = true) {
+    assert(isWasmData());
+    IsPassive = V;
+  }
   static bool classof(const MCSection *S) { return S->getVariant() == SV_Wasm; }
 };
 
diff --git a/llvm/include/llvm/ObjectYAML/WasmYAML.h b/llvm/include/llvm/ObjectYAML/WasmYAML.h
index f5260bbb1ed..1d69d78e613 100644
--- a/llvm/include/llvm/ObjectYAML/WasmYAML.h
+++ b/llvm/include/llvm/ObjectYAML/WasmYAML.h
@@ -111,8 +111,9 @@ struct Relocation {
 };
 
 struct DataSegment {
-  uint32_t MemoryIndex;
   uint32_t SectionOffset;
+  uint32_t InitFlags;
+  uint32_t MemoryIndex;
   wasm::WasmInitExpr Offset;
   yaml::BinaryRef Content;
 };