[CodeGen] Implement post-opt linking option for builtin bitocdes (llvm#69371)

In this patch, we create a new ModulePass that mimics the LinkInModules
API from CodeGenAction.cpp, and a new command line option to enable the
pass. As part of the implementation, we needed to refactor the
BackendConsumer class definition into a new separate header (instead of
embedded in CodeGenAction.cpp). With this new pass, we can now re-link
bitcodes supplied via the -mlink-built-in bitcodes as part of the
RunOptimizationPipeline.

With the re-linking pass, we now handle cases where new device library
functions are introduced as part of the optimization pipeline.
Previously, these newly introduced functions (for example a fused sincos
call) would result in a linking error due to a missing function
definition. This new pass can be initiated via:

      -mllvm -relink-builtin-bitcode-postop

Also note we intentionally exclude bitcodes supplied via the
-mlink-bitcode-file option from the second linking step

Change-Id: I77b6e79e69b89feb8ca7c3ac6f792f6881a23129

Author: lamb-j

clang/include/clang/CodeGen/BackendUtil.h

@@ -30,6 +30,7 @@ namespace clang {
   class CodeGenOptions;
   class TargetOptions;
   class LangOptions;
+  class BackendConsumer;
 
   enum BackendAction {
     Backend_EmitAssembly,  ///< Emit native assembly files
@@ -45,7 +46,8 @@ namespace clang {
                          const TargetOptions &TOpts, const LangOptions &LOpts,
                          StringRef TDesc, llvm::Module *M, BackendAction Action,
                          llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
-                         std::unique_ptr<raw_pwrite_stream> OS);
+                         std::unique_ptr<raw_pwrite_stream> OS,
+                         BackendConsumer *BC = nullptr);
 
   void EmbedBitcode(llvm::Module *M, const CodeGenOptions &CGOpts,
                     llvm::MemoryBufferRef Buf);

clang/lib/CodeGen/BackendConsumer.h

@@ -0,0 +1,166 @@
+//===--- BackendConsumer.h - LLVM BackendConsumer Header File -------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_LIB_CODEGEN_BACKENDCONSUMER_H
+#define LLVM_CLANG_LIB_CODEGEN_BACKENDCONSUMER_H
+
+#include "clang/CodeGen/BackendUtil.h"
+#include "clang/CodeGen/CodeGenAction.h"
+
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/Support/Timer.h"
+
+namespace llvm {
+  class DiagnosticInfoDontCall;
+}
+
+namespace clang {
+class ASTContext;
+class CodeGenAction;
+class CoverageSourceInfo;
+
+class BackendConsumer : public ASTConsumer {
+  using LinkModule = CodeGenAction::LinkModule;
+
+  virtual void anchor();
+  DiagnosticsEngine &Diags;
+  BackendAction Action;
+  const HeaderSearchOptions &HeaderSearchOpts;
+  const CodeGenOptions &CodeGenOpts;
+  const TargetOptions &TargetOpts;
+  const LangOptions &LangOpts;
+  std::unique_ptr<raw_pwrite_stream> AsmOutStream;
+  ASTContext *Context;
+  IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS;
+
+  llvm::Timer LLVMIRGeneration;
+  unsigned LLVMIRGenerationRefCount;
+
+  /// True if we've finished generating IR. This prevents us from generating
+  /// additional LLVM IR after emitting output in HandleTranslationUnit. This
+  /// can happen when Clang plugins trigger additional AST deserialization.
+  bool IRGenFinished = false;
+
+  bool TimerIsEnabled = false;
+
+  std::unique_ptr<CodeGenerator> Gen;
+
+  SmallVector<LinkModule, 4> LinkModules;
+
+  // A map from mangled names to their function's source location, used for
+  // backend diagnostics as the Clang AST may be unavailable. We actually use
+  // the mangled name's hash as the key because mangled names can be very
+  // long and take up lots of space. Using a hash can cause name collision,
+  // but that is rare and the consequences are pointing to a wrong source
+  // location which is not severe. This is a vector instead of an actual map
+  // because we optimize for time building this map rather than time
+  // retrieving an entry, as backend diagnostics are uncommon.
+  std::vector<std::pair<llvm::hash_code, FullSourceLoc>>
+    ManglingFullSourceLocs;
+
+
+  // This is here so that the diagnostic printer knows the module a diagnostic
+  // refers to.
+  llvm::Module *CurLinkModule = nullptr;
+
+public:
+  BackendConsumer(BackendAction Action, DiagnosticsEngine &Diags,
+                  IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
+                  const HeaderSearchOptions &HeaderSearchOpts,
+                  const PreprocessorOptions &PPOpts,
+                  const CodeGenOptions &CodeGenOpts,
+                  const TargetOptions &TargetOpts,
+                  const LangOptions &LangOpts, const std::string &InFile,
+                  SmallVector<LinkModule, 4> LinkModules,
+                  std::unique_ptr<raw_pwrite_stream> OS, llvm::LLVMContext &C,
+                  CoverageSourceInfo *CoverageInfo = nullptr);
+
+  // This constructor is used in installing an empty BackendConsumer
+  // to use the clang diagnostic handler for IR input files. It avoids
+  // initializing the OS field.
+  BackendConsumer(BackendAction Action, DiagnosticsEngine &Diags,
+                  IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
+                  const HeaderSearchOptions &HeaderSearchOpts,
+                  const PreprocessorOptions &PPOpts,
+                  const CodeGenOptions &CodeGenOpts,
+                  const TargetOptions &TargetOpts,
+                  const LangOptions &LangOpts, llvm::Module *Module,
+                  SmallVector<LinkModule, 4> LinkModules, llvm::LLVMContext &C,
+                  CoverageSourceInfo *CoverageInfo = nullptr);
+
+  llvm::Module *getModule() const;
+  std::unique_ptr<llvm::Module> takeModule();
+
+  CodeGenerator *getCodeGenerator();
+
+  void HandleCXXStaticMemberVarInstantiation(VarDecl *VD) override;
+  void Initialize(ASTContext &Ctx) override;
+  bool HandleTopLevelDecl(DeclGroupRef D) override;
+  void HandleInlineFunctionDefinition(FunctionDecl *D) override;
+  void HandleInterestingDecl(DeclGroupRef D) override;
+  void HandleTranslationUnit(ASTContext &C) override;
+  void HandleTagDeclDefinition(TagDecl *D) override;
+  void HandleTagDeclRequiredDefinition(const TagDecl *D) override;
+  void CompleteTentativeDefinition(VarDecl *D) override;
+  void CompleteExternalDeclaration(VarDecl *D) override;
+  void AssignInheritanceModel(CXXRecordDecl *RD) override;
+  void HandleVTable(CXXRecordDecl *RD) override;
+
+
+ // Links each entry in LinkModules into our module.  Returns true on error.
+  bool LinkInModules(llvm::Module *M, bool ShouldLinkFiles = true);
+
+  /// Get the best possible source location to represent a diagnostic that
+  /// may have associated debug info.
+  const FullSourceLoc getBestLocationFromDebugLoc(
+    const llvm::DiagnosticInfoWithLocationBase &D,
+    bool &BadDebugInfo, StringRef &Filename,
+    unsigned &Line, unsigned &Column) const;
+
+  std::optional<FullSourceLoc> getFunctionSourceLocation(
+    const llvm::Function &F) const;
+
+  void DiagnosticHandlerImpl(const llvm::DiagnosticInfo &DI);
+  /// Specialized handler for InlineAsm diagnostic.
+  /// \return True if the diagnostic has been successfully reported, false
+  /// otherwise.
+  bool InlineAsmDiagHandler(const llvm::DiagnosticInfoInlineAsm &D);
+  /// Specialized handler for diagnostics reported using SMDiagnostic.
+  void SrcMgrDiagHandler(const llvm::DiagnosticInfoSrcMgr &D);
+  /// Specialized handler for StackSize diagnostic.
+  /// \return True if the diagnostic has been successfully reported, false
+  /// otherwise.
+  bool StackSizeDiagHandler(const llvm::DiagnosticInfoStackSize &D);
+  /// Specialized handler for ResourceLimit diagnostic.
+  /// \return True if the diagnostic has been successfully reported, false
+  /// otherwise.
+  bool ResourceLimitDiagHandler(const llvm::DiagnosticInfoResourceLimit &D);
+
+  /// Specialized handler for unsupported backend feature diagnostic.
+  void UnsupportedDiagHandler(const llvm::DiagnosticInfoUnsupported &D);
+  /// Specialized handlers for optimization remarks.
+  /// Note that these handlers only accept remarks and they always handle
+  /// them.
+  void EmitOptimizationMessage(const llvm::DiagnosticInfoOptimizationBase &D,
+                               unsigned DiagID);
+  void
+    OptimizationRemarkHandler(const llvm::DiagnosticInfoOptimizationBase &D);
+  void OptimizationRemarkHandler(
+    const llvm::OptimizationRemarkAnalysisFPCommute &D);
+  void OptimizationRemarkHandler(
+    const llvm::OptimizationRemarkAnalysisAliasing &D);
+  void OptimizationFailureHandler(
+    const llvm::DiagnosticInfoOptimizationFailure &D);
+  void DontCallDiagHandler(const llvm::DiagnosticInfoDontCall &D);
+  /// Specialized handler for misexpect warnings.
+  /// Note that misexpect remarks are emitted through ORE
+  void MisExpectDiagHandler(const llvm::DiagnosticInfoMisExpect &D);
+};
+
+} // namespace clang
+#endif