commit 84cecfcb3db7c3275ae2d64c419a752d9f5311d6
author Teresa Johnson <tejohnson@google.com> Fri Jan 11 18:32:07 2019 +0000
committer Teresa Johnson <tejohnson@google.com> Fri Jan 11 18:32:07 2019 +0000
tree 137b550e0763b8685551711c9a6829e232870ba6
parent 290a8398917a3d4ef521a0cfdb67e65238f0043a

[LTO] Add option to enable LTOUnit splitting, and disable unless needed

Summary:
Adds a new -f[no]split-lto-unit flag that is disabled by default to
control module splitting during ThinLTO. It is automatically enabled
for -fsanitize=cfi and -fwhole-program-vtables.

The new EnableSplitLTOUnit codegen flag is passed down to llvm
via a new module flag of the same name.

Depends on D53890.

Reviewers: pcc

Subscribers: ormris, mehdi_amini, inglorion, eraman, steven_wu, dexonsmith, cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D53891

llvm-svn: 350949

clang/lib/CodeGen/BackendUtil.cpp

diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 1311af9..3e06519 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -814,6 +814,8 @@
         if (!ThinLinkOS)
           return;
       }
+      TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
+                               CodeGenOpts.EnableSplitLTOUnit);
       PerModulePasses.add(createWriteThinLTOBitcodePass(
           *OS, ThinLinkOS ? &ThinLinkOS->os() : nullptr));
     } else {
@@ -824,12 +826,15 @@
            !CodeGenOpts.DisableLLVMPasses &&
            llvm::Triple(TheModule->getTargetTriple()).getVendor() !=
                llvm::Triple::Apple);
-      if (EmitLTOSummary && !TheModule->getModuleFlag("ThinLTO"))
-        TheModule->addModuleFlag(Module::Error, "ThinLTO", uint32_t(0));
+      if (EmitLTOSummary) {
+        if (!TheModule->getModuleFlag("ThinLTO"))
+          TheModule->addModuleFlag(Module::Error, "ThinLTO", uint32_t(0));
+        TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
+                                 CodeGenOpts.EnableSplitLTOUnit);
+      }
 
-      PerModulePasses.add(
-          createBitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists,
-                                  EmitLTOSummary));
+      PerModulePasses.add(createBitcodeWriterPass(
+          *OS, CodeGenOpts.EmitLLVMUseLists, EmitLTOSummary));
     }
     break;
 
@@ -1054,6 +1059,8 @@
         if (!ThinLinkOS)
           return;
       }
+      TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
+                               CodeGenOpts.EnableSplitLTOUnit);
       MPM.addPass(ThinLTOBitcodeWriterPass(*OS, ThinLinkOS ? &ThinLinkOS->os()
                                                            : nullptr));
     } else {
@@ -1064,11 +1071,14 @@
            !CodeGenOpts.DisableLLVMPasses &&
            llvm::Triple(TheModule->getTargetTriple()).getVendor() !=
                llvm::Triple::Apple);
-      if (EmitLTOSummary && !TheModule->getModuleFlag("ThinLTO"))
-        TheModule->addModuleFlag(Module::Error, "ThinLTO", uint32_t(0));
-
-      MPM.addPass(BitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists,
-                                    EmitLTOSummary));
+      if (EmitLTOSummary) {
+        if (!TheModule->getModuleFlag("ThinLTO"))
+          TheModule->addModuleFlag(Module::Error, "ThinLTO", uint32_t(0));
+        TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
+                                 CodeGenOpts.EnableSplitLTOUnit);
+      }
+      MPM.addPass(
+          BitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists, EmitLTOSummary));
     }
     break;