[llvm] a9b33ff - [ThinLTO][NewPM] Clean up dead code under -O0

[Arthur Eubanks via llvm-commits]

Author: Arthur Eubanks
Date: 2021-02-24T17:08:57-08:00
New Revision: a9b33ffb8f84f0f5b1c2253973ed04bc776bd710

URL: https://github.com/llvm/llvm-project/commit/a9b33ffb8f84f0f5b1c2253973ed04bc776bd710
DIFF: https://github.com/llvm/llvm-project/commit/a9b33ffb8f84f0f5b1c2253973ed04bc776bd710.diff

LOG: [ThinLTO][NewPM] Clean up dead code under -O0

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

This matches the legacy PM.

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D97414

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Passes/PassBuilder.cpp b/llvm/lib/Passes/PassBuilder.cpp
index bb7d800f8b4f..52f7026c40eb 100644
--- a/llvm/lib/Passes/PassBuilder.cpp
+++ b/llvm/lib/Passes/PassBuilder.cpp
@@ -1539,8 +1539,17 @@ ModulePassManager PassBuilder::buildThinLTODefaultPipeline(
     MPM.addPass(LowerTypeTestsPass(nullptr, ImportSummary));
   }
 
-  if (Level == OptimizationLevel::O0)
+  if (Level == OptimizationLevel::O0) {
+    // Run a second time to clean up any type tests left behind by WPD for use
+    // in ICP.
+    MPM.addPass(LowerTypeTestsPass(nullptr, nullptr, true));
+    // 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());

diff  --git a/llvm/test/Other/new-pm-O0-defaults.ll b/llvm/test/Other/new-pm-O0-defaults.ll
index 8900a77b1f22..b7cd5ecae795 100644
--- a/llvm/test/Other/new-pm-O0-defaults.ll
+++ b/llvm/test/Other/new-pm-O0-defaults.ll
@@ -35,6 +35,9 @@
 ; 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: LowerTypeTestsPass
+; 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