[clang] 53adfa8 - [clang] Do not duplicate "EnableSplitLTOUnit" module flag

[David Greene via cfe-commits]

Author: David Greene
Date: 2021-12-02T08:24:56-08:00
New Revision: 53adfa8750eaf4558c41a50f699616545eb0151b

URL: https://github.com/llvm/llvm-project/commit/53adfa8750eaf4558c41a50f699616545eb0151b
DIFF: https://github.com/llvm/llvm-project/commit/53adfa8750eaf4558c41a50f699616545eb0151b.diff

LOG: [clang] Do not duplicate "EnableSplitLTOUnit" module flag

If clang's output is set to bitcode and LTO is enabled, clang would
unconditionally add the flag to the module.  Unfortunately, if the input were a
bitcode or IR file and had the flag set, this would result in two copies of the
flag, which is illegal IR.  Guard the setting of the flag by checking whether it
already exists.  This follows existing practice for the related "ThinLTO" module
flag.

Differential Revision: https://reviews.llvm.org/D112177

Added: 
    clang/test/CodeGen/enable-split-lto-unit.ll

Modified: 
    clang/lib/CodeGen/BackendUtil.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 648c7b3df8ed4..510f3911939cf 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -1034,8 +1034,9 @@ void EmitAssemblyHelper::EmitAssemblyWithLegacyPassManager(
         if (!ThinLinkOS)
           return;
       }
-      TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
-                               CodeGenOpts.EnableSplitLTOUnit);
+      if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
+        TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
+                                 CodeGenOpts.EnableSplitLTOUnit);
       PerModulePasses.add(createWriteThinLTOBitcodePass(
           *OS, ThinLinkOS ? &ThinLinkOS->os() : nullptr));
     } else {
@@ -1049,8 +1050,9 @@ void EmitAssemblyHelper::EmitAssemblyWithLegacyPassManager(
       if (EmitLTOSummary) {
         if (!TheModule->getModuleFlag("ThinLTO"))
           TheModule->addModuleFlag(Module::Error, "ThinLTO", uint32_t(0));
-        TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
-                                 uint32_t(1));
+        if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
+          TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
+                                   uint32_t(1));
       }
 
       PerModulePasses.add(createBitcodeWriterPass(
@@ -1451,8 +1453,9 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
         if (!ThinLinkOS)
           return;
       }
-      TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
-                               CodeGenOpts.EnableSplitLTOUnit);
+      if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
+        TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
+                                 CodeGenOpts.EnableSplitLTOUnit);
       MPM.addPass(ThinLTOBitcodeWriterPass(*OS, ThinLinkOS ? &ThinLinkOS->os()
                                                            : nullptr));
     } else {
@@ -1465,8 +1468,9 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
       if (EmitLTOSummary) {
         if (!TheModule->getModuleFlag("ThinLTO"))
           TheModule->addModuleFlag(Module::Error, "ThinLTO", uint32_t(0));
-        TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
-                                 uint32_t(1));
+        if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
+          TheModule->addModuleFlag(Module::Error, "EnableSplitLTOUnit",
+                                   uint32_t(1));
       }
       MPM.addPass(
           BitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists, EmitLTOSummary));

diff  --git a/clang/test/CodeGen/enable-split-lto-unit.ll b/clang/test/CodeGen/enable-split-lto-unit.ll
new file mode 100644
index 0000000000000..2ca09a1ae3a8a
--- /dev/null
+++ b/clang/test/CodeGen/enable-split-lto-unit.ll
@@ -0,0 +1,25 @@
+; Test that we do not duplicate the EnableSplitLTOUnit module flag.
+;
+; Disable the verifier so the compiler doesn't abort and thus lead to empty
+; output and false pass.
+;
+; RUN: %clang_cc1 -fno-legacy-pass-manager -emit-llvm-bc -flto=full -disable-llvm-verifier -o - %s | llvm-dis | FileCheck %s --check-prefix=FULL-NPM
+; RUN: %clang_cc1 -fno-legacy-pass-manager -emit-llvm-bc -flto=thin -disable-llvm-verifier -o - %s | llvm-dis | FileCheck %s --check-prefix=THIN-NPM
+; RUN: %clang_cc1 -flegacy-pass-manager -emit-llvm-bc -flto=full -disable-llvm-verifier -o - %s | llvm-dis | FileCheck %s --check-prefix=FULL-OPM
+; RUN: %clang_cc1 -flegacy-pass-manager -emit-llvm-bc -flto=thin -disable-llvm-verifier -o - %s | llvm-dis | FileCheck %s --check-prefix=THIN-OPM
+
+define dso_local void @main() local_unnamed_addr {
+entry:
+  ret void
+}
+
+; FULL-NPM-NOT: !llvm.module.flags = !{!0, !1, !2, !3, !3}
+; FULL-OPM-NOT: !llvm.module.flags = !{!0, !1, !2, !3, !3}
+; THIN-NPM-NOT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
+; THIN-OPM-NOT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
+!llvm.module.flags = !{!0, !1, !2, !3}
+
+!0 = !{i32 1, !"wchar_size", i32 2}
+!1 = !{i32 7, !"frame-pointer", i32 2}
+!2 = !{i32 1, !"ThinLTO", i32 0}
+!3 = !{i32 1, !"EnableSplitLTOUnit", i32 1}