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

[via llvm-commits]

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@@ -0,0 +1,61 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Instrumentation/PGOForceFunctionAttrs.h"
+#include "llvm/Analysis/BlockFrequencyInfo.h"
+#include "llvm/Analysis/ProfileSummaryInfo.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/Support/ErrorHandling.h"
+
+using namespace llvm;
+
+static bool shouldRunOnFunction(Function &F, ProfileSummaryInfo &PSI,
+                                FunctionAnalysisManager &FAM) {
+  if (F.isDeclaration())
+    return false;
+  // Respect existing attributes.
+  if (F.hasOptNone() || F.hasOptSize() || F.hasMinSize())
+    return false;
+  if (F.hasFnAttribute(Attribute::Cold))
+    return true;
+  if (!PSI.hasProfileSummary())
+    return false;
+  BlockFrequencyInfo &BFI = FAM.getResult<BlockFrequencyAnalysis>(F);
+  return PSI.isFunctionColdInCallGraph(&F, BFI);
+}
+
+PreservedAnalyses PGOForceFunctionAttrsPass::run(Module &M,
+                                                 ModuleAnalysisManager &AM) {
+  if (ColdType == PGOOptions::ColdFuncOpt::Default)
+    return PreservedAnalyses::all();
+  ProfileSummaryInfo &PSI = AM.getResult<ProfileSummaryAnalysis>(M);
+  FunctionAnalysisManager &FAM =
+      AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
+  bool MadeChange = false;
+  for (Function &F : M) {
+    if (!shouldRunOnFunction(F, PSI, FAM))
+      continue;
+    MadeChange = true;
+    switch (ColdType) {
+    case PGOOptions::ColdFuncOpt::Default:
+      llvm_unreachable("bailed out for default above");
+      break;
+    case PGOOptions::ColdFuncOpt::OptSize:
+      F.addFnAttr(Attribute::OptimizeForSize);
+      break;
+    case PGOOptions::ColdFuncOpt::MinSize:
+      F.addFnAttr(Attribute::MinSize);
+      break;
+    case PGOOptions::ColdFuncOpt::OptNone:
+      F.addFnAttr(Attribute::OptimizeNone);
+      F.addFnAttr(Attribute::NoInline);
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WenleiHe wrote:

What if functions originally has `AlwaysInline` attribute? 

More generally, what if function originally has a conflicting attribute from what's being set here? 

https://github.com/llvm/llvm-project/pull/69030