[SampleFDO] Skip profile reading when flattened profile used in ThinLTO postlink

If the sample profile has no inlining hierachy information included, we call
the sample profile is flattened. For flattened profile, in ThinLTO postlink
phase, SampleProfileLoader's hot function inlining and profile annotation will
do nothing, so it is better to save the effort to read in the profile and run
the sample profile loader pass. It is helpful for reducing compile time when
the flattened profile is huge.

Differential Revision: https://reviews.llvm.org/D54819

llvm-svn: 351476

1 files changed, 15 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index b92d3ba4f48..1dd07fa026a 100644
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -104,6 +104,10 @@ static cl::opt<bool>
     EnablePrepareForThinLTO("prepare-for-thinlto", cl::init(false), cl::Hidden,
                             cl::desc("Enable preparation for ThinLTO."));
 
+static cl::opt<bool>
+    EnablePerformThinLTO("perform-thinlto", cl::init(false), cl::Hidden,
+                         cl::desc("Enable performing ThinLTO."));
+
 cl::opt<bool> EnableHotColdSplit("hot-cold-split", cl::init(false), cl::Hidden,
     cl::desc("Enable hot-cold splitting pass"));
 
@@ -146,6 +150,11 @@ static cl::opt<bool>
     EnableCHR("enable-chr", cl::init(true), cl::Hidden,
               cl::desc("Enable control height reduction optimization (CHR)"));
 
+cl::opt<bool> FlattenedProfileUsed(
+    "flattened-profile-used", cl::init(false), cl::Hidden,
+    cl::desc("Indicate the sample profile being used is flattened, i.e., "
+             "no inline hierachy exists in the profile. "));
+
 PassManagerBuilder::PassManagerBuilder() {
     OptLevel = 2;
     SizeLevel = 0;
@@ -166,7 +175,7 @@ PassManagerBuilder::PassManagerBuilder() {
     PGOInstrUse = "";
     PGOSampleUse = "";
     PrepareForThinLTO = EnablePrepareForThinLTO;
-    PerformThinLTO = false;
+    PerformThinLTO = EnablePerformThinLTO;
     DivergentTarget = false;
 }
 
@@ -414,7 +423,11 @@ void PassManagerBuilder::populateModulePassManager(
     legacy::PassManagerBase &MPM) {
   if (!PGOSampleUse.empty()) {
     MPM.add(createPruneEHPass());
-    MPM.add(createSampleProfileLoaderPass(PGOSampleUse));
+    // In ThinLTO mode, when flattened profile is used, all the available
+    // profile information will be annotated in PreLink phase so there is
+    // no need to load the profile again in PostLink.
+    if (!(FlattenedProfileUsed && PerformThinLTO))
+      MPM.add(createSampleProfileLoaderPass(PGOSampleUse));
   }
 
   // Allow forcing function attributes as a debugging and tuning aid.