LowerTypeTests: Propagate symver directives

Summary:
This change fixes https://crbug.com/834474, a build failure caused by
LowerTypeTests not preserving .symver symbol versioning directives for
exported functions. Emit symver information to ThinLTO summary data and
then propagate symver directives for exported functions to the merged
module.

Emitting symver information to the summaries increases the size of
intermediate build artifacts for a Chromium build by less than 0.2%.

Reviewers: pcc

Reviewed By: pcc

Subscribers: tejohnson, mehdi_amini, eraman, llvm-commits, eugenis, kcc

Differential Revision: https://reviews.llvm.org/D45798

llvm-svn: 330387

include/llvm/Object/ModuleSymbolTable.h

@@ -57,6 +57,15 @@ public:
   static void CollectAsmSymbols(
       const Module &M,
       function_ref<void(StringRef, object::BasicSymbolRef::Flags)> AsmSymbol);
+
+  /// Parse inline ASM and collect the symvers directives that are defined in
+  /// the current module.
+  ///
+  /// For each found symbol, call \p AsmSymver with the name of the symbol and
+  /// its alias.
+  static void
+  CollectAsmSymvers(const Module &M,
+                    function_ref<void(StringRef, StringRef)> AsmSymver);
 };
 
 } // end namespace llvm

lib/Object/ModuleSymbolTable.cpp

@@ -68,9 +68,9 @@ void ModuleSymbolTable::addModule(Module *M) {
   });
 }
 
-void ModuleSymbolTable::CollectAsmSymbols(
-    const Module &M,
-    function_ref<void(StringRef, BasicSymbolRef::Flags)> AsmSymbol) {
+static void
+initializeRecordStreamer(const Module &M,
+                         function_ref<void(RecordStreamer &)> Init) {
   StringRef InlineAsm = M.getModuleInlineAsm();
   if (InlineAsm.empty())
     return;
@@ -119,6 +119,13 @@ void ModuleSymbolTable::CollectAsmSymbols(
   if (Parser->Run(false))
     return;
 
+  Init(Streamer);
+}
+
+void ModuleSymbolTable::CollectAsmSymbols(
+    const Module &M,
+    function_ref<void(StringRef, BasicSymbolRef::Flags)> AsmSymbol) {
+  initializeRecordStreamer(M, [&](RecordStreamer &Streamer) {
     Streamer.flushSymverDirectives();
 
     for (auto &KV : Streamer) {
@@ -149,6 +156,16 @@ void ModuleSymbolTable::CollectAsmSymbols(
       }
       AsmSymbol(Key, BasicSymbolRef::Flags(Res));
     }
+  });
+}
+
+void ModuleSymbolTable::CollectAsmSymvers(
+    const Module &M, function_ref<void(StringRef, StringRef)> AsmSymver) {
+  initializeRecordStreamer(M, [&](RecordStreamer &Streamer) {
+    for (auto &KV : Streamer.symverAliases())
+      for (auto &Alias : KV.second)
+        AsmSymver(KV.first->getName(), Alias);
+  });
 }
 
 void ModuleSymbolTable::printSymbolName(raw_ostream &OS, Symbol S) const {

lib/Object/RecordStreamer.cpp

@@ -128,6 +128,11 @@ void RecordStreamer::emitELFSymverDirective(StringRef AliasName,
   SymverAliasMap[Aliasee].push_back(AliasName);
 }
 
+iterator_range<RecordStreamer::const_symver_iterator>
+RecordStreamer::symverAliases() {
+  return {SymverAliasMap.begin(), SymverAliasMap.end()};
+}
+
 void RecordStreamer::flushSymverDirectives() {
   // Mapping from mangled name to GV.
   StringMap<const GlobalValue *> MangledNameMap;

lib/Object/RecordStreamer.h

@@ -47,10 +47,6 @@ private:
 public:
   RecordStreamer(MCContext &Context, const Module &M);
 
-  using const_iterator = StringMap<State>::const_iterator;
-
-  const_iterator begin();
-  const_iterator end();
   void EmitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
                        bool) override;
   void EmitLabel(MCSymbol *Symbol, SMLoc Loc = SMLoc()) override;
@@ -63,9 +59,19 @@ public:
   /// Record .symver aliases for later processing.
   void emitELFSymverDirective(StringRef AliasName,
                               const MCSymbol *Aliasee) override;
+
   // Emit ELF .symver aliases and ensure they have the same binding as the
   // defined symbol they alias with.
   void flushSymverDirectives();
+
+  // Symbols iterators
+  using const_iterator = StringMap<State>::const_iterator;
+  const_iterator begin();
+  const_iterator end();
+
+  // SymverAliasMap iterators
+  using const_symver_iterator = decltype(SymverAliasMap)::const_iterator;
+  iterator_range<const_symver_iterator> symverAliases();
 };
 
 } // end namespace llvm

lib/Transforms/IPO/LowerTypeTests.cpp

@@ -1947,6 +1947,24 @@ bool LowerTypeTestsModule::lower() {
     }
   }
 
+  // Emit .symver directives for exported functions, if they exist.
+  if (ExportSummary) {
+    if (NamedMDNode *SymversMD = M.getNamedMetadata("symvers")) {
+      for (auto Symver : SymversMD->operands()) {
+        assert(Symver->getNumOperands() >= 2);
+        StringRef SymbolName =
+            cast<MDString>(Symver->getOperand(0))->getString();
+        StringRef Alias = cast<MDString>(Symver->getOperand(1))->getString();
+
+        if (!ExportedFunctions.count(SymbolName))
+          continue;
+
+        M.appendModuleInlineAsm(
+            (llvm::Twine(".symver ") + SymbolName + ", " + Alias).str());
+      }
+    }
+  }
+
   return true;
 }
 

lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp

@@ -18,6 +18,7 @@
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/PassManager.h"
+#include "llvm/Object/ModuleSymbolTable.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/raw_ostream.h"
@@ -301,13 +302,13 @@ void splitAndWriteThinLTOBitcode(
   promoteInternals(*MergedM, M, ModuleId, CfiFunctions);
   promoteInternals(M, *MergedM, ModuleId, CfiFunctions);
 
+  auto &Ctx = MergedM->getContext();
   SmallVector<MDNode *, 8> CfiFunctionMDs;
   for (auto V : CfiFunctions) {
     Function &F = *cast<Function>(V);
     SmallVector<MDNode *, 2> Types;
     F.getMetadata(LLVMContext::MD_type, Types);
 
-    auto &Ctx = MergedM->getContext();
     SmallVector<Metadata *, 4> Elts;
     Elts.push_back(MDString::get(Ctx, F.getName()));
     CfiFunctionLinkage Linkage;
@@ -336,7 +337,6 @@ void splitAndWriteThinLTOBitcode(
       continue;
 
     auto *F = cast<Function>(A.getAliasee());
-    auto &Ctx = MergedM->getContext();
     SmallVector<Metadata *, 4> Elts;
 
     Elts.push_back(MDString::get(Ctx, A.getName()));
@@ -355,6 +355,25 @@ void splitAndWriteThinLTOBitcode(
       NMD->addOperand(MD);
   }
 
+  SmallVector<MDNode *, 8> Symvers;
+  ModuleSymbolTable::CollectAsmSymvers(M, [&](StringRef Name, StringRef Alias) {
+    Function *F = M.getFunction(Name);
+    if (!F || F->use_empty())
+      return;
+
+    SmallVector<Metadata *, 2> Elts;
+    Elts.push_back(MDString::get(Ctx, Name));
+    Elts.push_back(MDString::get(Ctx, Alias));
+
+    Symvers.push_back(MDTuple::get(Ctx, Elts));
+  });
+
+  if (!Symvers.empty()) {
+    NamedMDNode *NMD = MergedM->getOrInsertNamedMetadata("symvers");
+    for (auto MD : Symvers)
+      NMD->addOperand(MD);
+  }
+
   simplifyExternals(*MergedM);
 
   // FIXME: Try to re-use BSI and PFI from the original module here.

test/Transforms/LowerTypeTests/export-symver.ll

@@ -0,0 +1,16 @@
+; RUN: opt -S %s -lowertypetests -lowertypetests-summary-action=export -lowertypetests-read-summary=%S/Inputs/use-typeid1-typeid2.yaml | FileCheck %s
+;
+; CHECK: module asm ".symver exported_and_symver, alias1"
+; CHECK-NOT: .symver exported
+; CHECK-NOT: .symver symver
+
+target triple = "x86_64-unknown-linux"
+
+!cfi.functions = !{!0, !1}
+!symvers = !{!3, !4}
+
+!0 = !{!"exported_and_symver", i8 2, !2}
+!1 = !{!"exported", i8 2, !2}
+!2 = !{i64 0, !"typeid1"}
+!3 = !{!"exported_and_symver", !"alias1"}
+!4 = !{!"symver", !"alias2"}

test/Transforms/ThinLTOBitcodeWriter/symver.ll

@@ -0,0 +1,22 @@
+; RUN: opt -thinlto-bc -o %t %s
+; RUN: llvm-modextract -n 1 -o - %t | llvm-dis | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+module asm ".symver used, used@VER"
+module asm ".symver unused, unused@VER"
+module asm ".symver variable, variable@VER"
+
+declare !type !0 void @used()
+declare !type !0 void @unused()
+@variable = global i32 0
+
+define i32* @use() {
+  call void @used()
+  ret i32* @variable
+}
+
+; CHECK: !symvers = !{![[SYMVER:[0-9]+]]}
+; CHECK: ![[SYMVER]] = !{!"used", !"used@VER"}
+
+!0 = !{i64 0, !"_ZTSFvvE"}