[hot-cold-split] Add opt remark on success

[tejohnson]

Summary

Emit optimization remark on successful hot cold split.

[sebpop]

ok

lib/Transforms/IPO/HotColdSplitting.cpp

if (PSI->isFunctionEntryCold(&F))
     return false;
   return true;
 }
 
 Function *
 HotColdSplitting::extractColdRegion(const SmallVectorImpl<BasicBlock *> &Region,
                                     DominatorTree *DT, BlockFrequencyInfo *BFI,
                                     OptimizationRemarkEmitter &ORE) {
+  assert(!Region.empty());
   LLVM_DEBUG(for (auto *BB : Region)
           llvm::dbgs() << "\nExtracting: " << *BB;);
 
   // TODO: Pass BFI and BPI to update profile information.
   CodeExtractor CE(Region, DT);
 
   SetVector<Value *> Inputs, Outputs, Sinks;
   CE.findInputsOutputs(Inputs, Outputs, Sinks);
 
   // Do not extract regions that have live exit variables.
   if (Outputs.size() > 0)
     return nullptr;
 
+  Function *OrigF = Region[0]->getParent();
   if (Function *OutF = CE.extractCodeRegion()) {
     User *U = *OutF->user_begin();
     CallInst *CI = cast<CallInst>(U);
     CallSite CS(CI);
     NumColdSESEOutlined++;
     if (GetTTI(*OutF).useColdCCForColdCall(*OutF)) {
       OutF->setCallingConv(CallingConv::Cold);
       CS.setCallingConv(CallingConv::Cold);
     }
     CI->setIsNoInline();
     LLVM_DEBUG(llvm::dbgs() << "Outlined Region: " << *OutF);
+    ORE.emit([&]() {
+      return OptimizationRemark(DEBUG_TYPE, "HotColdSplit",
+                                &*Region[0]->begin())
+             << ore::NV("Original", OrigF) << " split cold code into "
+             << ore::NV("Split", OutF);
+    });
     return OutF;
   }
 
   ORE.emit([&]() {
     return OptimizationRemarkMissed(DEBUG_TYPE, "ExtractFailed",
                                     &*Region[0]->begin())
            << "Failed to extract region at block "
            << ore::NV("Block", Region.front());

test/Transforms/HotColdSplit/split-cold-2.ll

-; RUN: opt -hotcoldsplit -S < %s | FileCheck %s
-; RUN: opt -passes=hotcoldsplit -S < %s | FileCheck %s
+; RUN: opt -hotcoldsplit -pass-remarks=hotcoldsplit -S < %s 2>&1 | FileCheck %s
+; RUN: opt -passes=hotcoldsplit -pass-remarks=hotcoldsplit -S < %s 2>&1 | FileCheck %s
 
 ; Make sure this compiles. This test used to fail with an invalid phi node: the
 ; two predecessors were outlined and the SSA representation was invalid.
 
+; CHECK: remark: <unknown>:0:0: fun split cold code into fun_if.else
 ; CHECK-LABEL: @fun
 ; CHECK: codeRepl:
 ; CHECK-NEXT: call void @fun_if.else
 
 define void @fun() {
 entry:
   br i1 undef, label %if.then, label %if.else