[PGO] Profile guided code size optimization.

Summary:
Enable some of the existing size optimizations for cold code under PGO.

A ~5% code size saving in big internal app under PGO.

The way it gets BFI/PSI is discussed in the RFC thread

http://lists.llvm.org/pipermail/llvm-dev/2019-March/130894.html 

Note it doesn't currently touch loop passes.

Reviewers: davidxl, eraman

Reviewed By: eraman

Subscribers: mgorny, javed.absar, smeenai, mehdi_amini, eraman, zzheng, steven_wu, dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59514

llvm-svn: 358422

1 files changed, 37 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/SizeOpts.cpp b/llvm/lib/Transforms/Utils/SizeOpts.cpp
new file mode 100644
index 00000000000..1519751197d
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/SizeOpts.cpp
@@ -0,0 +1,37 @@
+//===-- SizeOpts.cpp - code size optimization related code ----------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains some shared code size optimization related code.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/BlockFrequencyInfo.h"
+#include "llvm/Analysis/ProfileSummaryInfo.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Transforms/Utils/SizeOpts.h"
+using namespace llvm;
+
+static cl::opt<bool> ProfileGuidedSizeOpt(
+    "pgso", cl::Hidden, cl::init(true),
+    cl::desc("Enable the profile guided size optimization. "));
+
+bool llvm::shouldOptimizeForSize(Function *F, ProfileSummaryInfo *PSI,
+                                 BlockFrequencyInfo *BFI) {
+  assert(F);
+  if (!PSI || !BFI || !PSI->hasProfileSummary())
+    return false;
+  return ProfileGuidedSizeOpt && PSI->isFunctionColdInCallGraph(F, *BFI);
+}
+
+bool llvm::shouldOptimizeForSize(BasicBlock *BB, ProfileSummaryInfo *PSI,
+                                 BlockFrequencyInfo *BFI) {
+  assert(BB);
+  if (!PSI || !BFI || !PSI->hasProfileSummary())
+    return false;
+  return ProfileGuidedSizeOpt && PSI->isColdBlock(BB, BFI);
+}