[AlwaysInline] Avoid unnecessary BFI fetches (#117750)

AlwaysInliner doesn't use BFI itself, it only updates it. If BFI is not
already computed, it will spend time to first compute it, and then
update it. This is not necessary: If BFI is not available in the first
place, there is no need to update it.

This is mainly relevant in debug builds for IR that has a lot of
alwaysinline functions.

Author: nikic

llvm/lib/Transforms/IPO/AlwaysInliner.cpp

@@ -34,7 +34,8 @@ bool AlwaysInlineImpl(
     Module &M, bool InsertLifetime, ProfileSummaryInfo &PSI,
     function_ref<AssumptionCache &(Function &)> GetAssumptionCache,
     function_ref<AAResults &(Function &)> GetAAR,
-    function_ref<BlockFrequencyInfo &(Function &)> GetBFI) {
+    function_ref<BlockFrequencyInfo &(Function &)> GetBFI,
+    function_ref<BlockFrequencyInfo *(Function &)> GetCachedBFI) {
   SmallSetVector<CallBase *, 16> Calls;
   bool Changed = false;
   SmallVector<Function *, 16> InlinedComdatFunctions;
@@ -61,9 +62,11 @@ bool AlwaysInlineImpl(
       DebugLoc DLoc = CB->getDebugLoc();
       BasicBlock *Block = CB->getParent();
 
-      InlineFunctionInfo IFI(GetAssumptionCache, &PSI,
-                             GetBFI ? &GetBFI(*Caller) : nullptr,
-                             GetBFI ? &GetBFI(F) : nullptr);
+      // Only update CallerBFI if already available. The CallerBFI update
+      // requires CalleeBFI.
+      BlockFrequencyInfo *CallerBFI = GetCachedBFI(*Caller);
+      InlineFunctionInfo IFI(GetAssumptionCache, &PSI, CallerBFI,
+                             CallerBFI ? &GetBFI(F) : nullptr);
 
       InlineResult Res = InlineFunction(*CB, IFI, /*MergeAttributes=*/true,
                                         &GetAAR(F), InsertLifetime);
@@ -133,9 +136,12 @@ struct AlwaysInlinerLegacyPass : public ModulePass {
     auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & {
       return getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
     };
+    auto GetCachedBFI = [](Function &) -> BlockFrequencyInfo * {
+      return nullptr;
+    };
 
     return AlwaysInlineImpl(M, InsertLifetime, PSI, GetAssumptionCache, GetAAR,
-                            /*GetBFI*/ nullptr);
+                            /*GetBFI=*/nullptr, GetCachedBFI);
   }
 
   static char ID; // Pass identification, replacement for typeid
@@ -172,13 +178,16 @@ PreservedAnalyses AlwaysInlinerPass::run(Module &M,
   auto GetBFI = [&](Function &F) -> BlockFrequencyInfo & {
     return FAM.getResult<BlockFrequencyAnalysis>(F);
   };
+  auto GetCachedBFI = [&](Function &F) -> BlockFrequencyInfo * {
+    return FAM.getCachedResult<BlockFrequencyAnalysis>(F);
+  };
   auto GetAAR = [&](Function &F) -> AAResults & {
     return FAM.getResult<AAManager>(F);
   };
   auto &PSI = MAM.getResult<ProfileSummaryAnalysis>(M);
 
   bool Changed = AlwaysInlineImpl(M, InsertLifetime, PSI, GetAssumptionCache,
-                                  GetAAR, GetBFI);
+                                  GetAAR, GetBFI, GetCachedBFI);
 
   return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
 }