From 488d1dc0edefb3b9852e1fd1ea579d585f7acec7 Mon Sep 17 00:00:00 2001
From: Teresa Johnson <tejohnson@google.com>
Date: Thu, 23 Mar 2017 19:47:49 +0000
Subject: [PATCH] [ThinLTO] Clang support for emitting minimized bitcode for
 thin link

Summary:
Clang companion patch to LLVM patch 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 D31027.

Reviewers: mehdi_amini, pcc

Subscribers: cfe-commits, Prazek

Differential Revision: https://reviews.llvm.org/D31050

llvm-svn: 298639
---
 clang/include/clang/Driver/CC1Options.td      |  2 ++
 clang/include/clang/Frontend/CodeGenOptions.h |  5 +++++
 clang/lib/CodeGen/BackendUtil.cpp             | 19 +++++++++++++++++--
 clang/lib/Frontend/CompilerInvocation.cpp     |  1 +
 clang/test/CodeGen/thin_link_bitcode.c        |  9 +++++++++
 5 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/CodeGen/thin_link_bitcode.c

diff --git a/clang/include/clang/Driver/CC1Options.td b/clang/include/clang/Driver/CC1Options.td
index acc76f6..a683efe 100644
--- a/clang/include/clang/Driver/CC1Options.td
+++ b/clang/include/clang/Driver/CC1Options.td
@@ -312,6 +312,8 @@ def flto_visibility_public_std:
 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
diff --git a/clang/include/clang/Frontend/CodeGenOptions.h b/clang/include/clang/Frontend/CodeGenOptions.h
index f8f3266..b17f190 100644
--- a/clang/include/clang/Frontend/CodeGenOptions.h
+++ b/clang/include/clang/Frontend/CodeGenOptions.h
@@ -188,6 +188,11 @@ public:
   /// 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.
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 35c31a0..35de1a45 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -686,13 +686,28 @@ void EmitAssemblyHelper::EmitAssembly(BackendAction Action,
   CodeGenPasses.add(
       createTargetTransformInfoWrapperPass(getTargetIRAnalysis()));
 
+  std::unique_ptr<raw_fd_ostream> ThinLinkOS;
+
   switch (Action) {
   case Backend_EmitNothing:
     break;
 
   case Backend_EmitBC:
-    if (CodeGenOpts.EmitSummaryIndex)
-      PerModulePasses.add(createWriteThinLTOBitcodePass(*OS));
+    if (CodeGenOpts.EmitSummaryIndex) {
+      if (!CodeGenOpts.ThinLinkBitcodeFile.empty()) {
+        std::error_code EC;
+        ThinLinkOS.reset(new llvm::raw_fd_ostream(
+            CodeGenOpts.ThinLinkBitcodeFile, EC,
+            llvm::sys::fs::F_None));
+        if (EC) {
+          Diags.Report(diag::err_fe_unable_to_open_output) << CodeGenOpts.ThinLinkBitcodeFile
+                                                           << EC.message();
+          return;
+        }
+      }
+      PerModulePasses.add(
+          createWriteThinLTOBitcodePass(*OS, ThinLinkOS.get()));
+    }
     else
       PerModulePasses.add(
           createBitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists));
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 01ac69e..c193620 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -641,6 +641,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
           << 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);
 
diff --git a/clang/test/CodeGen/thin_link_bitcode.c b/clang/test/CodeGen/thin_link_bitcode.c
new file mode 100644
index 0000000..4cb5f79
--- /dev/null
+++ b/clang/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
-- 
2.7.4