1 files changed, 58 insertions, 0 deletions
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
index b0a80b0ca79..c8a53ebd4cc 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
@@ -21,8 +21,10 @@
 #include "WebAssemblyMCInstLower.h"
 #include "WebAssemblyMachineFunctionInfo.h"
 #include "WebAssemblyRegisterInfo.h"
+#include "WebAssemblyTargetMachine.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/BinaryFormat/Wasm.h"
 #include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/AsmPrinter.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
@@ -159,6 +161,7 @@ void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
   }
 
   EmitProducerInfo(M);
+  EmitTargetFeatures();
 }
 
 void WebAssemblyAsmPrinter::EmitProducerInfo(Module &M) {
@@ -212,6 +215,61 @@ void WebAssemblyAsmPrinter::EmitProducerInfo(Module &M) {
   }
 }
 
+void WebAssemblyAsmPrinter::EmitTargetFeatures() {
+  static const std::pair<unsigned, const char *> FeaturePairs[] = {
+      {WebAssembly::FeatureAtomics, "atomics"},
+      {WebAssembly::FeatureBulkMemory, "bulk-memory"},
+      {WebAssembly::FeatureExceptionHandling, "exception-handling"},
+      {WebAssembly::FeatureNontrappingFPToInt, "nontrapping-fptoint"},
+      {WebAssembly::FeatureSignExt, "sign-ext"},
+      {WebAssembly::FeatureSIMD128, "simd128"},
+  };
+
+  struct FeatureEntry {
+    uint8_t Prefix;
+    StringRef Name;
+  };
+
+  FeatureBitset UsedFeatures =
+      static_cast<WebAssemblyTargetMachine &>(TM).getUsedFeatures();
+
+  // Calculate the features and linkage policies to emit
+  SmallVector<FeatureEntry, 4> EmittedFeatures;
+  for (auto &F : FeaturePairs) {
+    FeatureEntry Entry;
+    Entry.Name = F.second;
+    if (F.first == WebAssembly::FeatureAtomics) {
+      // "atomics" is special: code compiled without atomics may have had its
+      // atomics lowered to nonatomic operations. Such code would be dangerous
+      // to mix with proper atomics, so it is always Required or Disallowed.
+      Entry.Prefix = UsedFeatures[F.first] ? wasm::WASM_FEATURE_PREFIX_REQUIRED
+                                           : wasm::WASM_FEATURE_PREFIX_DISALLOWED;
+      EmittedFeatures.push_back(Entry);
+    } else {
+      // Other features are marked Used or not mentioned
+      if (UsedFeatures[F.first]) {
+        Entry.Prefix = wasm::WASM_FEATURE_PREFIX_USED;
+        EmittedFeatures.push_back(Entry);
+      }
+    }
+  }
+
+  // Emit features and linkage policies into the "target_features" section
+  MCSectionWasm *FeaturesSection = OutContext.getWasmSection(
+      ".custom_section.target_features", SectionKind::getMetadata());
+  OutStreamer->PushSection();
+  OutStreamer->SwitchSection(FeaturesSection);
+
+  OutStreamer->EmitULEB128IntValue(EmittedFeatures.size());
+  for (auto &F : EmittedFeatures) {
+    OutStreamer->EmitIntValue(F.Prefix, 1);
+    OutStreamer->EmitULEB128IntValue(F.Name.size());
+    OutStreamer->EmitBytes(F.Name);
+  }
+
+  OutStreamer->PopSection();
+}
+
 void WebAssemblyAsmPrinter::EmitConstantPool() {
   assert(MF->getConstantPool()->getConstants().empty() &&
          "WebAssembly disables constant pools");