[PGO] Add ability to mark cold functions as optsize/minsize/optnone (#69030)

The performance of cold functions shouldn't matter too much, so if we
care about binary sizes, add an option to mark cold functions as
optsize/minsize for binary size, or optnone for compile times [1]. Clang
patch will be in a future patch.

This is intended to replace `shouldOptimizeForSize(Function&, ...)`.
We've seen multiple cases where calls to this expensive function, if not
careful, can blow up compile times. I will clean up users of that
function in a followup patch.

Initial version: https://reviews.llvm.org/D149800

[1]
https://discourse.llvm.org/t/rfc-new-feature-proposal-de-optimizing-cold-functions-using-pgo-info/56388

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index 4e233d9..142bd50 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -74,6 +74,7 @@
 #include "llvm/Transforms/Instrumentation/InstrOrderFile.h"
 #include "llvm/Transforms/Instrumentation/InstrProfiling.h"
 #include "llvm/Transforms/Instrumentation/MemProfiler.h"
+#include "llvm/Transforms/Instrumentation/PGOForceFunctionAttrs.h"
 #include "llvm/Transforms/Instrumentation/PGOInstrumentation.h"
 #include "llvm/Transforms/Scalar/ADCE.h"
 #include "llvm/Transforms/Scalar/AlignmentFromAssumptions.h"
@@ -213,6 +214,12 @@ static cl::opt<bool>
                            cl::desc("Enable DFA jump threading"),
                            cl::init(false), cl::Hidden);
 
+// TODO: turn on and remove flag
+static cl::opt<bool> EnablePGOForceFunctionAttrs(
+    "enable-pgo-force-function-attrs",
+    cl::desc("Enable pass to set function attributes based on PGO profiles"),
+    cl::init(false));
+
 static cl::opt<bool>
     EnableHotColdSplit("hot-cold-split",
                        cl::desc("Enable hot-cold splitting pass"));
@@ -1146,6 +1153,9 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
   if (EnableSyntheticCounts && !PGOOpt)
     MPM.addPass(SyntheticCountsPropagation());
 
+  if (EnablePGOForceFunctionAttrs)
+    MPM.addPass(PGOForceFunctionAttrsPass(PGOOpt->ColdOptType));
+
   MPM.addPass(AlwaysInlinerPass(/*InsertLifetimeIntrinsics=*/true));
 
   if (EnableModuleInliner)