Disable loop unrolling and icp in SamplePGO ThinLTO compile phase

Summary:
loop unrolling and icp will make the sample profile annotation much harder in the backend. So disable these 2 optimization in the ThinLTO compile phase.
Will add a test in cfe in a separate patch.

Reviewers: tejohnson

Reviewed By: tejohnson

Subscribers: mehdi_amini, llvm-commits, Prazek

Differential Revision: https://reviews.llvm.org/D31217

llvm-svn: 298646

1 files changed, 12 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index 734f81b0877..b07b7d1b5ff 100644
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -435,6 +435,14 @@ void PassManagerBuilder::populateModulePassManager(
     MPM.add(createPGOIndirectCallPromotionLegacyPass(/*InLTO = */ true,
                                                      !PGOSampleUse.empty()));
 
+  // For SamplePGO in ThinLTO compile phase, we do not want to unroll loops
+  // as it will change the CFG too much to make the 2nd profile annotation
+  // in backend more difficult.
+  bool PrepareForThinLTOUsingPGOSampleProfile =
+      PrepareForThinLTO && !PGOSampleUse.empty();
+  if (PrepareForThinLTOUsingPGOSampleProfile)
+    DisableUnrollLoops = true;
+
   if (!DisableUnitAtATime) {
     // Infer attributes about declarations if possible.
     MPM.add(createInferFunctionAttrsLegacyPass());
@@ -453,7 +461,10 @@ void PassManagerBuilder::populateModulePassManager(
     MPM.add(createCFGSimplificationPass()); // Clean up after IPCP & DAE
   }
 
-  if (!PerformThinLTO) {
+  // For SamplePGO in ThinLTO compile phase, we do not want to do indirect
+  // call promotion as it will change the CFG too much to make the 2nd
+  // profile annotation in backend more difficult.
+  if (!PerformThinLTO && !PrepareForThinLTOUsingPGOSampleProfile) {
     /// PGO instrumentation is added during the compile phase for ThinLTO, do
     /// not run it a second time
     addPGOInstrPasses(MPM);