[LinkerWrapper] Relax ordering of static libraries for offloading (#87532)

Summary:
The linker wrapper attempts to maintain consistent semantics with
existing host invocations. Static libraries by default only extract if
there are non-weak symbols that remain undefined. However, we have
situations between linkers that put different meanings on ordering. The
ld.bfd linker requires static libraries to be defined after the symbols,
while `ld.lld` relaxes this rule. The linker wrapper went with the
former as it's the easier solution, however this has caused a lot of
issues as I've had to explain this rule to several people, it also make
it difficult to include things like `libc` in the OpenMP runtime because
it would sometimes be linked before or after.

This patch reworks the logic to more or less perform the following logic
for static libraries.

  1. Split library / object inputs.
  2. Include every object input and record its undefined symbols
  3. Repeatedly try to extract static libraries to resolve these
     symbols. If a file is extracted we need to check every library
     again to resolve any new undefined symbols.

This allows the following to work and will cause fewer issues when
replacing HIP, which does `--whole-archive` so it's very likely the old
logic will regress.
```console
$ clang -lfoo main.c -fopenmp --offload-arch=native
```

Author: jhuber6

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

@@ -44,6 +44,8 @@ int bar() { return weak; }
 // 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: clang-linker-wrapper --host-triple=x86_64-unknown-linux-gnu --dry-run \
+// RUN:   --linker-path=/usr/bin/ld %t.a %t.o -o a.out 2>&1 \
 // RUN: | FileCheck %s --check-prefix=LIBRARY-RESOLVES
 
 // LIBRARY-RESOLVES: clang{{.*}} -o {{.*}}.img --target=amdgcn-amd-amdhsa -mcpu=gfx1030 {{.*}}.o {{.*}}.o
@@ -66,6 +68,8 @@ int bar() { return weak; }
 // 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: clang-linker-wrapper --host-triple=x86_64-unknown-linux-gnu --dry-run \
+// RUN:   --linker-path=/usr/bin/ld %t.a %t.o -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

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

@@ -1448,9 +1448,9 @@ getDeviceInput(const ArgList &Args) {
   StringSaver Saver(Alloc);
 
   // Try to extract device code from the linker input files.
-  DenseMap<OffloadFile::TargetID, SmallVector<OffloadFile>> InputFiles;
-  DenseMap<OffloadFile::TargetID, DenseMap<StringRef, Symbol>> Syms;
   bool WholeArchive = Args.hasArg(OPT_wholearchive_flag) ? true : false;
+  SmallVector<OffloadFile> ObjectFilesToExtract;
+  SmallVector<OffloadFile> ArchiveFilesToExtract;
   for (const opt::Arg *Arg : Args.filtered(
            OPT_INPUT, OPT_library, OPT_whole_archive, OPT_no_whole_archive)) {
     if (Arg->getOption().matches(OPT_whole_archive) ||
@@ -1486,50 +1486,87 @@ getDeviceInput(const ArgList &Args) {
     if (Error Err = extractOffloadBinaries(Buffer, Binaries))
       return std::move(Err);
 
-    // We only extract archive members that are needed.
-    bool IsArchive = identify_magic(Buffer.getBuffer()) == file_magic::archive;
-    bool Extracted = true;
-    while (Extracted) {
-      Extracted = false;
-      for (OffloadFile &Binary : Binaries) {
-        // If the binary was previously extracted it will be set to null.
-        if (!Binary.getBinary())
+    for (auto &OffloadFile : Binaries) {
+      if (identify_magic(Buffer.getBuffer()) == file_magic::archive &&
+          !WholeArchive)
+        ArchiveFilesToExtract.emplace_back(std::move(OffloadFile));
+      else
+        ObjectFilesToExtract.emplace_back(std::move(OffloadFile));
+    }
+  }
+
+  // Link all standard input files and update the list of symbols.
+  DenseMap<OffloadFile::TargetID, SmallVector<OffloadFile>> InputFiles;
+  DenseMap<OffloadFile::TargetID, DenseMap<StringRef, Symbol>> Syms;
+  for (OffloadFile &Binary : ObjectFilesToExtract) {
+    if (!Binary.getBinary())
+      continue;
+
+    SmallVector<OffloadFile::TargetID> CompatibleTargets = {Binary};
+    for (const auto &[ID, Input] : InputFiles)
+      if (object::areTargetsCompatible(Binary, ID))
+        CompatibleTargets.emplace_back(ID);
+
+    for (const auto &[Index, ID] : llvm::enumerate(CompatibleTargets)) {
+      Expected<bool> ExtractOrErr = getSymbols(
+          Binary.getBinary()->getImage(), Binary.getBinary()->getOffloadKind(),
+          /*IsArchive=*/false, Saver, Syms[ID]);
+      if (!ExtractOrErr)
+        return ExtractOrErr.takeError();
+
+      // If another target needs this binary it must be copied instead.
+      if (Index == CompatibleTargets.size() - 1)
+        InputFiles[ID].emplace_back(std::move(Binary));
+      else
+        InputFiles[ID].emplace_back(Binary.copy());
+    }
+  }
+
+  // Archive members only extract if they define needed symbols. We do this
+  // after every regular input file so that libraries may be included out of
+  // order. This follows 'ld.lld' semantics which are more lenient.
+  bool Extracted = true;
+  while (Extracted) {
+    Extracted = false;
+    for (OffloadFile &Binary : ArchiveFilesToExtract) {
+      // If the binary was previously extracted it will be set to null.
+      if (!Binary.getBinary())
+        continue;
+
+      SmallVector<OffloadFile::TargetID> CompatibleTargets = {Binary};
+      for (const auto &[ID, Input] : InputFiles)
+        if (object::areTargetsCompatible(Binary, ID))
+          CompatibleTargets.emplace_back(ID);
+
+      for (const auto &[Index, ID] : llvm::enumerate(CompatibleTargets)) {
+        // Only extract an if we have an an object matching this target.
+        if (!InputFiles.count(ID))
           continue;
 
-        SmallVector<OffloadFile::TargetID> CompatibleTargets = {Binary};
-        for (const auto &[ID, Input] : InputFiles)
-          if (object::areTargetsCompatible(Binary, ID))
-            CompatibleTargets.emplace_back(ID);
-
-        for (const auto &[Index, ID] : llvm::enumerate(CompatibleTargets)) {
-          // Only extract an if we have an an object matching this target.
-          if (IsArchive && !WholeArchive && !InputFiles.count(ID))
-            continue;
-
-          Expected<bool> ExtractOrErr = getSymbols(
-              Binary.getBinary()->getImage(),
-              Binary.getBinary()->getOffloadKind(), IsArchive, Saver, Syms[ID]);
-          if (!ExtractOrErr)
-            return ExtractOrErr.takeError();
-
-          Extracted = !WholeArchive && *ExtractOrErr;
-
-          // Skip including the file if it is an archive that does not resolve
-          // any symbols.
-          if (IsArchive && !WholeArchive && !Extracted)
-            continue;
-
-          // If another target needs this binary it must be copied instead.
-          if (Index == CompatibleTargets.size() - 1)
-            InputFiles[ID].emplace_back(std::move(Binary));
-          else
-            InputFiles[ID].emplace_back(Binary.copy());
-        }
+        Expected<bool> ExtractOrErr =
+            getSymbols(Binary.getBinary()->getImage(),
+                       Binary.getBinary()->getOffloadKind(), /*IsArchive=*/true,
+                       Saver, Syms[ID]);
+        if (!ExtractOrErr)
+          return ExtractOrErr.takeError();
 
-        // If we extracted any files we need to check all the symbols again.
-        if (Extracted)
-          break;
+        Extracted = *ExtractOrErr;
+
+        // Skip including the file if it is an archive that does not resolve
+        // any symbols.
+        if (!Extracted)
+          continue;
+
+        // If another target needs this binary it must be copied instead.
+        if (Index == CompatibleTargets.size() - 1)
+          InputFiles[ID].emplace_back(std::move(Binary));
+        else
+          InputFiles[ID].emplace_back(Binary.copy());
       }
+
+      // If we extracted any files we need to check all the symbols again.
+      if (Extracted)
+        break;
     }
   }