[ThinLTO] Add importing stats to thin link

[tejohnson]

Summary

Previously we could only get the number of imported functions and
variables from the backend. This adds stats to the thin link where the
importing is decided.

lib/Transforms/IPO/FunctionImport.cpp

 #include <system_error>
 #include <tuple>
 #include <utility>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "function-import"
 
-STATISTIC(NumImportedFunctions, "Number of functions imported");
-STATISTIC(NumImportedGlobalVars, "Number of global variables imported");
+STATISTIC(NumImportedFunctionsThinLink,
+          "Number of functions thin link decided to import");
+STATISTIC(NumImportedHotFunctionsThinLink,
+          "Number of hot functions thin link decided to import");
+STATISTIC(NumImportedCriticalFunctionsThinLink,
+          "Number of critical functions thin link decided to import");
+STATISTIC(NumImportedGlobalVarsThinLink,
+          "Number of global variables thin link decided to import");
+STATISTIC(NumImportedFunctions, "Number of functions imported in backend");
+STATISTIC(NumImportedGlobalVars,
+          "Number of global variables imported in backend");
 STATISTIC(NumImportedModules, "Number of modules imported from");
 STATISTIC(NumDeadSymbols, "Number of dead stripped symbols in index");
 STATISTIC(NumLiveSymbols, "Number of live symbols in index");
 
 /// Limit on instruction count of imported functions.
 static cl::opt<unsigned> ImportInstrLimit(
     "import-instr-limit", cl::init(100), cl::Hidden, cl::value_desc("N"),
     cl::desc("Only import functions with less than N instructions"));
for (auto &VI : Summary.refs()) {
 
     LLVM_DEBUG(dbgs() << " ref -> " << VI << "\n");
 
     for (auto &RefSummary : VI.getSummaryList())
       if (RefSummary->getSummaryKind() == GlobalValueSummary::GlobalVarKind &&
           !RefSummary->notEligibleToImport() &&
           !GlobalValue::isInterposableLinkage(RefSummary->linkage()) &&
           RefSummary->refs().empty()) {
-        ImportList[RefSummary->modulePath()].insert(VI.getGUID());
+        auto ILI = ImportList[RefSummary->modulePath()].insert(VI.getGUID());
+        // Only update stat if we haven't already imported this variable.
+        if (ILI.second)
+          NumImportedGlobalVarsThinLink++;
         if (ExportLists)
           (*ExportLists)[RefSummary->modulePath()].insert(VI.getGUID());
         break;
       }
   }
 }
 
 static const char *
for (auto &Edge : Summary.calls()) {
 
     auto IT = ImportThresholds.insert(std::make_pair(
         VI.getGUID(), std::make_tuple(NewThreshold, nullptr, nullptr)));
     bool PreviouslyVisited = !IT.second;
     auto &ProcessedThreshold = std::get<0>(IT.first->second);
     auto &CalleeSummary = std::get<1>(IT.first->second);
     auto &FailureInfo = std::get<2>(IT.first->second);
 
+    bool IsHotCallsite =
+        Edge.second.getHotness() == CalleeInfo::HotnessType::Hot;
+    bool IsCriticalCallsite =
+        Edge.second.getHotness() == CalleeInfo::HotnessType::Critical;
+
     const FunctionSummary *ResolvedCalleeSummary = nullptr;
     if (CalleeSummary) {
       assert(PreviouslyVisited);
       // Since the traversal of the call graph is DFS, we can revisit a function
       // a second time with a higher threshold. In this case, it is added back
       // to the worklist with the new threshold (so that its own callee chains
       // can be considered with the higher threshold).
       if (NewThreshold <= ProcessedThreshold) {
if (CalleeSummary) {
       assert(ResolvedCalleeSummary->instCount() <= NewThreshold &&
              "selectCallee() didn't honor the threshold");
 
       auto ExportModulePath = ResolvedCalleeSummary->modulePath();
       auto ILI = ImportList[ExportModulePath].insert(VI.getGUID());
       // We previously decided to import this GUID definition if it was already
       // inserted in the set of imports from the exporting module.
       bool PreviouslyImported = !ILI.second;
+      if (!PreviouslyImported) {
+        NumImportedFunctionsThinLink++;
+        if (IsHotCallsite)
+          NumImportedHotFunctionsThinLink++;
+        if (IsCriticalCallsite)
+          NumImportedCriticalFunctionsThinLink++;
+      }
 
       // Make exports in the source module.
       if (ExportLists) {
         auto &ExportList = (*ExportLists)[ExportModulePath];
         ExportList.insert(VI.getGUID());
         if (!PreviouslyImported) {
           // This is the first time this function was exported from its source
           // module, so mark all functions and globals it references as exported
auto GetAdjustedThreshold = [](unsigned Threshold, bool IsHotCallsite) {
       // Adjust the threshold for next level of imported functions.
       // The threshold is different for hot callsites because we can then
       // inline chains of hot calls.
       if (IsHotCallsite)
         return Threshold * ImportHotInstrFactor;
       return Threshold * ImportInstrFactor;
     };
 
-    bool IsHotCallsite =
-        Edge.second.getHotness() == CalleeInfo::HotnessType::Hot;
     const auto AdjThreshold = GetAdjustedThreshold(Threshold, IsHotCallsite);
 
     ImportCount++;
 
     // Insert the newly imported function to the worklist.
     Worklist.emplace_back(ResolvedCalleeSummary, AdjThreshold, VI.getGUID());
   }
 }

test/Transforms/FunctionImport/Inputs/import_stats.ll

+; ModuleID = 'import_stats2.ll'
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @hot() {
+  ret void
+}
+define void @critical() {
+  ret void
+}
+define void @none() {
+  ret void
+}

test/Transforms/FunctionImport/import_stats.ll

+; Test to check thin link importing stats
+
+; RUN: opt -module-summary %s -o %t.bc
+; RUN: opt -module-summary %p/Inputs/import_stats.ll -o %t2.bc
+
+; Test thin link stats with both new and old LTO
+; RUN: llvm-lto -thinlto-action=run -stats %t.bc %t2.bc \
+; RUN:    2>&1 | FileCheck %s --check-prefix=THINLINKSTATS
+; RUN: llvm-lto2 run -stats -o %t3 %t.bc %t2.bc \
+; RUN:          -r %t.bc,hot_function,plx \
+; RUN:          -r %t.bc,hot, \
+; RUN:          -r %t.bc,critical, \
+; RUN:          -r %t.bc,none, \
+; RUN:          -r %t2.bc,hot,plx \
+; RUN:          -r %t2.bc,critical,plx \
+; RUN:          -r %t2.bc,none,plx \
+; RUN:          2>&1 | FileCheck %s --check-prefix=THINLINKSTATS
+
+; THINLINKSTATS-DAG: 1 function-import  - Number of critical functions thin link decided to import
+; THINLINKSTATS-DAG: 3 function-import  - Number of functions thin link decided to import
+; THINLINKSTATS-DAG: 1 function-import  - Number of hot functions thin link decided to import
+
+; ModuleID = 'import_stats.ll'
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; This function has a high profile count, so entry block is hot.
+define void @hot_function(i1 %a) !prof !20 {
+entry:
+  call void @hot()
+  call void @critical()
+  br i1 %a, label %None1, label %None2, !prof !42
+None1:          ; half goes here
+  call void @none()
+  br label %exit
+None2:          ; half goes here
+  br label %exit
+exit:
+  ret void
+}
+
+declare void @hot()
+declare void @none()
+declare void @critical()
+
+!42 = !{!"branch_weights", i32 1, i32 1}
+
+!llvm.module.flags = !{!1}
+!20 = !{!"function_entry_count", i64 100, i64 696010031887058302}
+
+!1 = !{i32 1, !"ProfileSummary", !2}
+!2 = !{!3, !4, !5, !6, !7, !8, !9, !10}
+!3 = !{!"ProfileFormat", !"InstrProf"}
+!4 = !{!"TotalCount", i64 300}
+!5 = !{!"MaxCount", i64 100}
+!6 = !{!"MaxInternalCount", i64 100}
+!7 = !{!"MaxFunctionCount", i64 100}
+!8 = !{!"NumCounts", i64 4}
+!9 = !{!"NumFunctions", i64 1}
+!10 = !{!"DetailedSummary", !11}
+!11 = !{!12, !13, !14}
+!12 = !{i32 10000, i64 100, i32 1}
+!13 = !{i32 999000, i64 100, i32 1}
+!14 = !{i32 999999, i64 1, i32 4}