[LinkerWrapper] Do not extract globals with no offloading language

[jhuber6]

Summary

The linker wrapper needs to reinvent its own special static library
handling for static libraries containing fatbinaries. This is primarily
because offloading languages expect certain global symbols to be visible
to the host so we must consider them used symbols. However we should be
able to remove this requirement if we are linking in "freestanding" code
that was not created by an offloading language.

The motivation for this is to support the work-in-progress libc for
GPUs. It is provided as a static library with no offloading language
set. This logic will let us only import used libc symbols always.

[jhuber6]

Remove whitespace

[jhuber6]

ping

[yaxunl]

LGTM. Thanks.

clang/test/Driver/linker-wrapper-libs.c

 // RUN: clang-linker-wrapper --host-triple=x86_64-unknown-linux-gnu --dry-run \
 // RUN:   --linker-path=/usr/bin/ld -- %t.o %t.a -o a.out 2>&1 \
 // RUN: | FileCheck %s --check-prefix=LIBRARY-GLOBAL
 
 // LIBRARY-GLOBAL: clang{{.*}} -o {{.*}}.img --target=amdgcn-amd-amdhsa -mcpu=gfx1030 {{.*}}.o {{.*}}.o
 // LIBRARY-GLOBAL: clang{{.*}} -o {{.*}}.img --target=nvptx64-nvidia-cuda -march=sm_70 {{.*}}.s {{.*}}.o
 
 //
+// Check that we do not extract a global symbol if the source file was not
+// created by an offloading language that expects there to be a host version of
+// the symbol.
+//
+// RUN: %clang -cc1 %s -triple nvptx64-nvidia-cuda -emit-llvm-bc -DGLOBAL -o %t.nvptx.global.bc
+// RUN: %clang -cc1 %s -triple amdgcn-amd-amdhsa -emit-llvm-bc -DGLOBAL -o %t.amdgpu.global.bc
+// RUN: clang-offload-packager -o %t-lib.out \
+// RUN:   --image=file=%t.nvptx.global.bc,triple=nvptx64-nvidia-cuda,arch=sm_70 \
+// RUN:   --image=file=%t.amdgpu.global.bc,triple=amdgcn-amd-amdhsa,arch=gfx1030
+// RUN: %clang -cc1 %s -triple x86_64-unknown-linux-gnu -emit-obj -o %t.o -fembed-offload-object=%t-lib.out
+// RUN: llvm-ar rcs %t.a %t.o
+// RUN: clang-offload-packager -o %t.out \
+// RUN:   --image=file=%t.elf.o,kind=openmp,triple=nvptx64-nvidia-cuda,arch=sm_70 \
+// RUN:   --image=file=%t.elf.o,kind=openmp,triple=amdgcn-amd-amdhsa,arch=gfx1030
+// RUN: %clang -cc1 %s -triple x86_64-unknown-linux-gnu -emit-obj -o %t.o -fembed-offload-object=%t.out
+// RUN: clang-linker-wrapper --host-triple=x86_64-unknown-linux-gnu --dry-run \
+// RUN:   --linker-path=/usr/bin/ld -- %t.o %t.a -o a.out 2>&1 \
+// RUN: | FileCheck %s --check-prefix=LIBRARY-GLOBAL-NONE
+
+// LIBRARY-GLOBAL-NONE-NOT: clang{{.*}} -o {{.*}}.img --target=amdgcn-amd-amdhsa -mcpu=gfx1030 {{.*}}.o {{.*}}.o
+// LIBRARY-GLOBAL-NONE-NOT: clang{{.*}} -o {{.*}}.img --target=nvptx64-nvidia-cuda -march=sm_70 {{.*}}.s {{.*}}.o
+
+//
 // Check that we do not extract an external weak symbol.
 //
 // RUN: %clang -cc1 %s -triple nvptx64-nvidia-cuda -emit-llvm-bc -DWEAK -o %t.nvptx.weak.bc
 // RUN: %clang -cc1 %s -triple amdgcn-amd-amdhsa -emit-llvm-bc -DWEAK -o %t.amdgpu.weak.bc
 // RUN: clang-offload-packager -o %t-lib.out \
 // RUN:   --image=file=%t.nvptx.weak.bc,kind=openmp,triple=nvptx64-nvidia-cuda,arch=sm_70 \
 // RUN:   --image=file=%t.amdgpu.weak.bc,kind=openmp,triple=amdgcn-amd-amdhsa,arch=gfx1030
 // RUN: %clang -cc1 %s -triple x86_64-unknown-linux-gnu -emit-obj -o %t.o -fembed-offload-object=%t-lib.out

clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp

 enum Symbol : uint32_t {
   Sym_None = 0,
   Sym_Undefined = 1U << 1,
   Sym_Weak = 1U << 2,
 };
 
 /// Scan the symbols from a BitcodeFile \p Buffer and record if we need to
 /// extract any symbols from it.
-Expected<bool> getSymbolsFromBitcode(MemoryBufferRef Buffer, StringSaver &Saver,
+Expected<bool> getSymbolsFromBitcode(MemoryBufferRef Buffer, OffloadKind Kind,
+                                     StringSaver &Saver,
                                      DenseMap<StringRef, Symbol> &Syms) {
   Expected<IRSymtabFile> IRSymtabOrErr = readIRSymtab(Buffer);
   if (!IRSymtabOrErr)
     return IRSymtabOrErr.takeError();
 
   bool ShouldExtract = false;
   for (unsigned I = 0; I != IRSymtabOrErr->Mods.size(); ++I) {
     for (const auto &Sym : IRSymtabOrErr->TheReader.module_symbols(I)) {
       if (Sym.isFormatSpecific() || !Sym.isGlobal())
         continue;
 
       bool NewSymbol = Syms.count(Sym.getName()) == 0;
       auto &OldSym = Syms[Saver.save(Sym.getName())];
 
       // We will extract if it defines a currenlty undefined non-weak symbol.
       bool ResolvesStrongReference =
           ((OldSym & Sym_Undefined && !(OldSym & Sym_Weak)) &&
            !Sym.isUndefined());
       // We will extract if it defines a new global symbol visible to the host.
+      // This is only necessary for code targeting an offloading language.
       bool NewGlobalSymbol =
           ((NewSymbol || (OldSym & Sym_Undefined)) && !Sym.isUndefined() &&
-           !Sym.canBeOmittedFromSymbolTable() &&
+           !Sym.canBeOmittedFromSymbolTable() && Kind != object::OFK_None &&
            (Sym.getVisibility() != GlobalValue::HiddenVisibility));
       ShouldExtract |= ResolvesStrongReference | NewGlobalSymbol;
 
       // Update this symbol in the "table" with the new information.
       if (OldSym & Sym_Undefined && !Sym.isUndefined())
         OldSym = static_cast<Symbol>(OldSym & ~Sym_Undefined);
       if (Sym.isUndefined() && NewSymbol)
         OldSym = static_cast<Symbol>(OldSym | Sym_Undefined);
       if (Sym.isWeak())
         OldSym = static_cast<Symbol>(OldSym | Sym_Weak);
     }
   }
 
   return ShouldExtract;
 }
 
 /// Scan the symbols from an ObjectFile \p Obj and record if we need to extract
 /// any symbols from it.
-Expected<bool> getSymbolsFromObject(const ObjectFile &Obj, StringSaver &Saver,
+Expected<bool> getSymbolsFromObject(const ObjectFile &Obj, OffloadKind Kind,
+                                    StringSaver &Saver,
                                     DenseMap<StringRef, Symbol> &Syms) {
   bool ShouldExtract = false;
   for (SymbolRef Sym : Obj.symbols()) {
     auto FlagsOrErr = Sym.getFlags();
     if (!FlagsOrErr)
       return FlagsOrErr.takeError();
 
     if (!(*FlagsOrErr & SymbolRef::SF_Global) ||
         (*FlagsOrErr & SymbolRef::SF_FormatSpecific))
       continue;
 
     auto NameOrErr = Sym.getName();
     if (!NameOrErr)
       return NameOrErr.takeError();
 
     bool NewSymbol = Syms.count(*NameOrErr) == 0;
     auto &OldSym = Syms[Saver.save(*NameOrErr)];
 
     // We will extract if it defines a currenlty undefined non-weak symbol.
     bool ResolvesStrongReference = (OldSym & Sym_Undefined) &&
                                    !(OldSym & Sym_Weak) &&
                                    !(*FlagsOrErr & SymbolRef::SF_Undefined);
 
     // We will extract if it defines a new global symbol visible to the host.
-    bool NewGlobalSymbol = ((NewSymbol || (OldSym & Sym_Undefined)) &&
-                            !(*FlagsOrErr & SymbolRef::SF_Undefined) &&
-                            !(*FlagsOrErr & SymbolRef::SF_Hidden));
+    // This is only necessary for code targeting an offloading language.
+    bool NewGlobalSymbol =
+        ((NewSymbol || (OldSym & Sym_Undefined)) &&
+         !(*FlagsOrErr & SymbolRef::SF_Undefined) && Kind != object::OFK_None &&
     ShouldExtract |= ResolvesStrongReference | NewGlobalSymbol;
 
     // Update this symbol in the "table" with the new information.
     if (OldSym & Sym_Undefined && !(*FlagsOrErr & SymbolRef::SF_Undefined))
       OldSym = static_cast<Symbol>(OldSym & ~Sym_Undefined);
     if (*FlagsOrErr & SymbolRef::SF_Undefined && NewSymbol)
       OldSym = static_cast<Symbol>(OldSym | Sym_Undefined);
     if (*FlagsOrErr & SymbolRef::SF_Weak)
       OldSym = static_cast<Symbol>(OldSym | Sym_Weak);
   }
   return ShouldExtract;
 }
 
 /// Attempt to 'resolve' symbols found in input files. We use this to
 /// determine if an archive member needs to be extracted. An archive member
 /// will be extracted if any of the following is true.
 ///   1) It defines an undefined symbol in a regular object filie.
 ///   2) It defines a global symbol without hidden visibility that has not
 ///      yet been defined.
-Expected<bool> getSymbols(StringRef Image, StringSaver &Saver,
+Expected<bool> getSymbols(StringRef Image, OffloadKind Kind, StringSaver &Saver,
                           DenseMap<StringRef, Symbol> &Syms) {
   MemoryBufferRef Buffer = MemoryBufferRef(Image, "");
   switch (identify_magic(Image)) {
   case file_magic::bitcode:
-    return getSymbolsFromBitcode(Buffer, Saver, Syms);
+    return getSymbolsFromBitcode(Buffer, Kind, Saver, Syms);
   case file_magic::elf_relocatable: {
     Expected<std::unique_ptr<ObjectFile>> ObjFile =
         ObjectFile::createObjectFile(Buffer);
     if (!ObjFile)
       return ObjFile.takeError();
-    return getSymbolsFromObject(**ObjFile, Saver, Syms);
+    return getSymbolsFromObject(**ObjFile, Kind, Saver, Syms);
   }
   default:
     return false;
   }
 }
 
 /// Search the input files and libraries for embedded device offloading code
 /// and add it to the list of files to be linked. Files coming from static
while (Extracted) {
         if (!Binary.getBinary())
           continue;
 
         // If we don't have an object file for this architecture do not
         // extract.
         if (IsArchive && !WholeArchive && !Syms.count(Binary))
           continue;
 
-        Expected<bool> ExtractOrErr =
-            getSymbols(Binary.getBinary()->getImage(), Saver, Syms[Binary]);
+        Expected<bool> ExtractOrErr = getSymbols(
+            Binary.getBinary()->getImage(),
+            Binary.getBinary()->getOffloadKind(), Saver, Syms[Binary]);
         if (!ExtractOrErr)
           return ExtractOrErr.takeError();
 
         Extracted = IsArchive && !WholeArchive && *ExtractOrErr;
 
         if (!IsArchive || WholeArchive || Extracted)
           InputFiles.emplace_back(std::move(Binary));