commit 45aef260ed0f17ee466d79c82300af1fd9c43450
author David Greene <david.greene@cerebras.net> Wed Oct 06 12:10:08 2021 -0700
committer Copybara-Service <copybara-worker@google.com> Thu Dec 02 08:31:27 2021 -0800
tree af8c2f71340922ea25830dd7674cca403bd41fd1
parent 72060d921de5da24cb86d5f859a7be5dd19b6601

[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

GitOrigin-RevId: 53adfa8750eaf4558c41a50f699616545eb0151b

lib/CodeGen/BackendUtil.cpp

diff --git a/lib/CodeGen/BackendUtil.cpp b/lib/CodeGen/BackendUtil.cpp
index 648c7b3..510f391 100644
--- a/lib/CodeGen/BackendUtil.cpp
+++ b/lib/CodeGen/BackendUtil.cpp
@@ -1034,8 +1034,9 @@
         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 @@
       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 @@
         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 @@
       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));

test/CodeGen/enable-split-lto-unit.ll

diff --git a/test/CodeGen/enable-split-lto-unit.ll b/test/CodeGen/enable-split-lto-unit.ll
new file mode 100644
index 0000000..2ca09a1
--- /dev/null
+++ b/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}