[PATCH] D97414: [ThinLTO] Clean up dead code under -O0

[Arthur Eubanks via Phabricator via llvm-commits]

aeubanks created this revision.
Herald added subscribers: hiraditya, inglorion.
aeubanks requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

We're running into undefined references using ThinLTO with -O0 on
Windows/Chrome. This fixes that.

This matches the legacy PM.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D97414

Files:
  llvm/lib/Passes/PassBuilder.cpp
  llvm/test/Other/new-pm-O0-defaults.ll


Index: llvm/test/Other/new-pm-O0-defaults.ll
===================================================================
--- llvm/test/Other/new-pm-O0-defaults.ll
+++ llvm/test/Other/new-pm-O0-defaults.ll
@@ -35,6 +35,8 @@
 ; CHECK-PRE-LINK-NEXT: Running pass: CanonicalizeAliasesPass
 ; CHECK-PRE-LINK-NEXT: Running pass: NameAnonGlobalPass
 ; CHECK-THINLTO-NEXT: Running pass: Annotation2MetadataPass
+; CHECK-THINLTO-NEXT: Running pass: EliminateAvailableExternallyPass
+; CHECK-THINLTO-NEXT: Running pass: GlobalDCEPass
 ; CHECK-LTO-NEXT: Running pass: Annotation2MetadataPass
 ; CHECK-LTO-NEXT: Running pass: WholeProgramDevirtPass
 ; CHECK-LTO-NEXT: Running analysis: InnerAnalysisManagerProxy
Index: llvm/lib/Passes/PassBuilder.cpp
===================================================================
--- llvm/lib/Passes/PassBuilder.cpp
+++ llvm/lib/Passes/PassBuilder.cpp
@@ -1539,8 +1539,14 @@
     MPM.addPass(LowerTypeTestsPass(nullptr, ImportSummary));
   }
 
-  if (Level == OptimizationLevel::O0)
+  if (Level == OptimizationLevel::O0) {
+    // Drop available_externally and unreferenced globals. This is necessary
+    // with ThinLTO in order to avoid leaving undefined references to dead
+    // globals in the object file.
+    MPM.addPass(EliminateAvailableExternallyPass());
+    MPM.addPass(GlobalDCEPass());
     return MPM;
+  }
 
   // Force any function attributes we want the rest of the pipeline to observe.
   MPM.addPass(ForceFunctionAttrsPass());


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