[ThinLTO] Indirect call promotion fixes for promoted local functions

Summary:
Fix a couple issues limiting the application of indirect call promotion
in ThinLTO mode:
- Invoke indirect call promotion before globalopt, since it may
  eliminate imported functions which appear unreferenced.
- Invoke indirect call promotion with InLTO=true so that the PGOFuncName
  metadata is used to get the name for locals which would have been
  renamed during promotion.

Reviewers: davidxl, mehdi_amini

Subscribers: Prazek, llvm-commits, mehdi_amini

Differential Revision: https://reviews.llvm.org/D24004

llvm-svn: 280024

1 files changed, 14 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index 71e479aac55..fd3aadb68fb 100644
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -405,6 +405,16 @@ void PassManagerBuilder::populateModulePassManager(
 
   addInitialAliasAnalysisPasses(MPM);
 
+  // For ThinLTO there are two passes of indirect call promotion. The
+  // first is during the compile phase when PerformThinLTO=false and
+  // intra-module indirect call targets are promoted. The second is during
+  // the ThinLTO backend when PerformThinLTO=true, when we promote imported
+  // inter-module indirect calls. For that we perform indirect call promotion
+  // earlier in the pass pipeline, here before globalopt. Otherwise imported
+  // available_externally functions look unreferenced and are removed.
+  if (PerformThinLTO)
+    MPM.add(createPGOIndirectCallPromotionLegacyPass(/*InLTO = */ true));
+
   if (!DisableUnitAtATime) {
     // Infer attributes about declarations if possible.
     MPM.add(createInferFunctionAttrsLegacyPass());
@@ -427,11 +437,12 @@ void PassManagerBuilder::populateModulePassManager(
     /// PGO instrumentation is added during the compile phase for ThinLTO, do
     /// not run it a second time
     addPGOInstrPasses(MPM);
+    // Indirect call promotion that promotes intra-module targets only.
+    // For ThinLTO this is done earlier due to interactions with globalopt
+    // for imported functions.
+    MPM.add(createPGOIndirectCallPromotionLegacyPass());
   }
 
-  // Indirect call promotion that promotes intra-module targets only.
-  MPM.add(createPGOIndirectCallPromotionLegacyPass());
-
   if (EnableNonLTOGlobalsModRef)
     // We add a module alias analysis pass here. In part due to bugs in the
     // analysis infrastructure this "works" in that the analysis stays alive