[WebAssembly] Add shared memory support to limits field

[dschuff]

Summary

Support the IS_SHARED bit in the memory limits flag word.
The compiler does not create object files with memory definitions, but the field is used by the linker.

[dschuff]

Object files currently import their memories, right? We should probably make that import shared when we use thread-model=posix.

include/llvm/BinaryFormat/Wasm.h

enum : unsigned {
   WASM_OPCODE_I32_CONST = 0x41,
   WASM_OPCODE_I64_CONST = 0x42,
   WASM_OPCODE_F32_CONST = 0x43,
   WASM_OPCODE_F64_CONST = 0x44,
 };
 
 enum : unsigned {
   WASM_LIMITS_FLAG_HAS_MAX = 0x1,
+  WASM_LIMITS_FLAG_IS_SHARED = 0x2,
 };
 
 // Kind codes used in the custom "name" section
 enum : unsigned {
   WASM_NAMES_FUNCTION = 0x1,
   WASM_NAMES_LOCAL = 0x2,
 };
 

lib/Object/WasmObjectFile.cpp

if (EndOpcode != wasm::WASM_OPCODE_END) {
     return make_error<GenericBinaryError>("Invalid init_expr",
                                           object_error::parse_failed);
   }
   return Error::success();
 }
 
 static wasm::WasmLimits readLimits(WasmObjectFile::ReadContext &Ctx) {
   wasm::WasmLimits Result;
-  Result.Flags = readVaruint1(Ctx);
+  Result.Flags = readVaruint32(Ctx);
   Result.Initial = readVaruint32(Ctx);
   if (Result.Flags & wasm::WASM_LIMITS_FLAG_HAS_MAX)
     Result.Maximum = readVaruint32(Ctx);
   return Result;
 }
 
 static wasm::WasmTable readTable(WasmObjectFile::ReadContext &Ctx) {
   wasm::WasmTable Table;

lib/ObjectYAML/WasmYAML.cpp

if (Info.Kind == wasm::WASM_SYMBOL_TYPE_FUNCTION) {
     llvm_unreachable("unsupported symbol kind");
   }
 }
 
 void ScalarBitSetTraits<WasmYAML::LimitFlags>::bitset(
     IO &IO, WasmYAML::LimitFlags &Value) {
 #define BCase(X) IO.bitSetCase(Value, #X, wasm::WASM_LIMITS_FLAG_##X)
   BCase(HAS_MAX);
+  BCase(IS_SHARED);
 #undef BCase
 }
 
 void ScalarBitSetTraits<WasmYAML::SegmentFlags>::bitset(
     IO &IO, WasmYAML::SegmentFlags &Value) {}
 
 void ScalarBitSetTraits<WasmYAML::SymbolFlags>::bitset(
     IO &IO, WasmYAML::SymbolFlags &Value) {

test/ObjectYAML/wasm/import_memory_shared.yaml

+# RUN: yaml2obj %s | obj2yaml | FileCheck %s
+--- !WASM
+FileHeader:
+  Version:         0x00000001
+Sections:
+  - Type:            TYPE
+    Signatures:
+      - Index:           0
+        ReturnType:      I32
+        ParamTypes:
+          - I32
+  - Type:            IMPORT
+    Imports:
+      - Module:          foo
+        Field:           imported_memory
+        Kind:            MEMORY
+        Memory:
+          Flags:           [ HAS_MAX, IS_SHARED ]
+          Initial:         0x00000010
+          Maximum:         0x00000011
+
+...
+# CHECK: --- !WASM
+# CHECK: FileHeader:
+# CHECK:   Version:           0x00000001
+# CHECK: Sections:
+# CHECK:   - Type:            IMPORT
+# CHECK:     Imports:         
+# CHECK:       - Module:          foo
+# CHECK:         Field:           imported_memory
+# CHECK:         Kind:            MEMORY
+# CHECK:         Memory:
+# CHECK:           Flags:           [ HAS_MAX, IS_SHARED ]
+# CHECK:           Initial:         0x00000010
+# CHECK:           Maximum:         0x00000011
+# CHECK: ...