[PATCH] D31050: [ThinLTO] Clang support for emitting minimized bitcode for thin link

[Teresa Johnson via Phabricator via cfe-commits]

tejohnson created this revision.
Herald added a subscriber: Prazek.

Clang companion patch to LLVM patch https://reviews.llvm.org/D31027, which adds support
for emitting minimized bitcode file for use in the thin link step.
Add a cc1 option -fthin-link-bitcode=<file> to trigger this behavior.

Depends on https://reviews.llvm.org/D31027.


https://reviews.llvm.org/D31050

Files:
  include/clang/Driver/CC1Options.td
  include/clang/Frontend/CodeGenOptions.h
  lib/CodeGen/BackendUtil.cpp
  lib/Frontend/CompilerInvocation.cpp
  test/CodeGen/thin_link_bitcode.c


Index: test/CodeGen/thin_link_bitcode.c
===================================================================
--- /dev/null
+++ test/CodeGen/thin_link_bitcode.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -o %t -flto=thin -fthin-link-bitcode=%t.nodebug -triple x86_64-unknown-linux-gnu -emit-llvm-bc -debug-info-kind=limited %s
+// RUN: llvm-bcanalyzer -dump %t | FileCheck %s
+// RUN: llvm-bcanalyzer -dump %t.nodebug | FileCheck %s --check-prefix=NO_DEBUG
+int main (void) {
+  return 0;
+}
+
+// CHECK: COMPILE_UNIT
+// NO_DEBUG-NOT: COMPILE_UNIT
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -641,6 +641,7 @@
           << A->getAsString(Args) << "-x ir";
     Opts.ThinLTOIndexFile = Args.getLastArgValue(OPT_fthinlto_index_EQ);
   }
+  Opts.ThinLinkBitcodeFile = Args.getLastArgValue(OPT_fthin_link_bitcode_EQ);
 
   Opts.MSVolatile = Args.hasArg(OPT_fms_volatile);
 
Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -688,7 +688,8 @@
 
   case Backend_EmitBC:
     if (CodeGenOpts.EmitSummaryIndex)
-      PerModulePasses.add(createWriteThinLTOBitcodePass(*OS));
+      PerModulePasses.add(
+          createWriteThinLTOBitcodePass(*OS, CodeGenOpts.ThinLinkBitcodeFile));
     else
       PerModulePasses.add(
           createBitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists));
Index: include/clang/Frontend/CodeGenOptions.h
===================================================================
--- include/clang/Frontend/CodeGenOptions.h
+++ include/clang/Frontend/CodeGenOptions.h
@@ -186,6 +186,11 @@
   /// importing.
   std::string ThinLTOIndexFile;
 
+  /// Name of a file that can optionally be written with minimized bitcode
+  /// to be used as input for the ThinLTO thin link step, which only needs
+  /// the summary and module symbol table (and not, e.g. any debug metadata).
+  std::string ThinLinkBitcodeFile;
+
   /// A list of file names passed with -fcuda-include-gpubinary options to
   /// forward to CUDA runtime back-end for incorporating them into host-side
   /// object file.
Index: include/clang/Driver/CC1Options.td
===================================================================
--- include/clang/Driver/CC1Options.td
+++ include/clang/Driver/CC1Options.td
@@ -312,6 +312,8 @@
 def flto_unit: Flag<["-"], "flto-unit">,
     HelpText<"Emit IR to support LTO unit features (CFI, whole program vtable opt)">;
 def fno_lto_unit: Flag<["-"], "fno-lto-unit">;
+def fthin_link_bitcode_EQ : Joined<["-"], "fthin-link-bitcode=">,
+    HelpText<"Write minimized bitcode to <file> for the ThinLTO thin link only">;
 
 //===----------------------------------------------------------------------===//
 // Dependency Output Options


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