[ThinLTO] Add optional import message and statistics

Summary:
Add a statistic to count the number of imported functions. Also, add a
new -print-imports option to emit a trace of imported functions, that
works even for an NDEBUG build.

Note that emitOptimizationRemark does not work for the above printing as
it expects a Function object and DebugLoc, neither of which we have
with summary-based importing.

This is part 2 of D18487, the first part was committed separately as
r264536.

Reviewers: joker.eph

Subscribers: llvm-commits, joker.eph

Differential Revision: http://reviews.llvm.org/D18487

llvm-svn: 264537

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 896ac5d3003..a99739c9ae8 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -14,6 +14,7 @@
 #include "llvm/Transforms/IPO/FunctionImport.h"
 
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/IR/AutoUpgrade.h"
 #include "llvm/IR/DiagnosticPrinter.h"
@@ -31,6 +32,8 @@
 
 using namespace llvm;
 
+STATISTIC(NumImported, "Number of functions imported");
+
 /// Limit on instruction count of imported functions.
 static cl::opt<unsigned> ImportInstrLimit(
     "import-instr-limit", cl::init(100), cl::Hidden, cl::value_desc("N"),
@@ -43,6 +46,9 @@ static cl::opt<float>
                                "`import-instr-limit` threshold by this factor "
                                "before processing newly imported functions"));
 
+static cl::opt<bool> PrintImports("print-imports", cl::init(false), cl::Hidden,
+                                  cl::desc("Print imported functions"));
+
 // Load lazily a module from \p FileName in \p Context.
 static std::unique_ptr<Module> loadFile(const std::string &FileName,
                                         LLVMContext &Context) {
@@ -348,6 +354,12 @@ bool FunctionImporter::importFunctions(
     if (renameModuleForThinLTO(*SrcModule, Index, &GlobalsToImport))
       return true;
 
+    if (PrintImports) {
+      for (const auto *GV : GlobalsToImport)
+        dbgs() << DestModule.getSourceFileName() << ": Import " << GV->getName()
+               << " from " << SrcModule->getSourceFileName() << "\n";
+    }
+
     if (TheLinker.linkInModule(std::move(SrcModule), Linker::Flags::None,
                                &GlobalsToImport))
       report_fatal_error("Function Import: link error");
@@ -355,6 +367,8 @@ bool FunctionImporter::importFunctions(
     ImportedCount += GlobalsToImport.size();
   }
 
+  NumImported += ImportedCount;
+
   DEBUG(dbgs() << "Imported " << ImportedCount << " functions for Module "
                << DestModule.getModuleIdentifier() << "\n");
   return ImportedCount;