[llvm] 0f946a5 - [InstrProf] Add option to disable loop opt after PGO

[Ellis Hoag via llvm-commits]

Author: Ellis Hoag
Date: 2022-08-17T12:23:18-07:00
New Revision: 0f946a50a485fe51f6a57335b660291ac05dab0b

URL: https://github.com/llvm/llvm-project/commit/0f946a50a485fe51f6a57335b660291ac05dab0b
DIFF: https://github.com/llvm/llvm-project/commit/0f946a50a485fe51f6a57335b660291ac05dab0b.diff

LOG: [InstrProf] Add option to disable loop opt after PGO

Add the `-enable-post-pgo-loop-rotation` option to enable or disable the loop rotation transformation [1]. With some instrumentations, e.g., function entry coverage [2], loop rotation is not necessary and can lead to some surprise differences in codegen, even for functions where instrumentation is blocked with `noprofile` or `skipprofile`. The default value is `true` so the default behavior does not change.

[1] https://www.llvm.org/docs/LoopTerminology.html#loop-terminology-loop-rotate
[2] https://reviews.llvm.org/D116180

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D131817

Added: 
    

Modified: 
    llvm/lib/Passes/PassBuilderPipelines.cpp

Removed: 
    


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diff  --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index 945ef512391b0..bd07638b37617 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -182,6 +182,10 @@ static cl::opt<bool> EnableMergeFunctions(
     "enable-merge-functions", cl::init(false), cl::Hidden,
     cl::desc("Enable function merging as part of the optimization pipeline"));
 
+static cl::opt<bool> EnablePostPGOLoopRotation(
+    "enable-post-pgo-loop-rotation", cl::init(true), cl::Hidden,
+    cl::desc("Run the loop rotation transformation after PGO instrumentation"));
+
 PipelineTuningOptions::PipelineTuningOptions() {
   LoopInterleaving = true;
   LoopVectorization = true;
@@ -664,13 +668,15 @@ void PassBuilder::addPGOInstrPasses(ModulePassManager &MPM,
   // Perform PGO instrumentation.
   MPM.addPass(PGOInstrumentationGen(IsCS));
 
-  // Disable header duplication in loop rotation at -Oz.
-  MPM.addPass(createModuleToFunctionPassAdaptor(
-      createFunctionToLoopPassAdaptor(
-          LoopRotatePass(Level != OptimizationLevel::Oz),
-          /*UseMemorySSA=*/false,
-          /*UseBlockFrequencyInfo=*/false),
-      PTO.EagerlyInvalidateAnalyses));
+  if (EnablePostPGOLoopRotation) {
+    // Disable header duplication in loop rotation at -Oz.
+    MPM.addPass(createModuleToFunctionPassAdaptor(
+        createFunctionToLoopPassAdaptor(
+            LoopRotatePass(Level != OptimizationLevel::Oz),
+            /*UseMemorySSA=*/false,
+            /*UseBlockFrequencyInfo=*/false),
+        PTO.EagerlyInvalidateAnalyses));
+  }
 
   // Add the profile lowering pass.
   InstrProfOptions Options;