[ThinLTO] Add an import cutoff for debugging/triaging

Summary:
Adds -import-cutoff=N which will stop importing during the thin link
after N imports. Default is -1 (no  limit).

Reviewers: wmi

Subscribers: inglorion, llvm-commits

Differential Revision: https://reviews.llvm.org/D45127

llvm-svn: 328934

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index d021b4a59a8..26d7db10880 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -71,6 +71,10 @@ 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"));
 
+static cl::opt<int> ImportCutoff(
+    "import-cutoff", cl::init(-1), cl::Hidden, cl::value_desc("N"),
+    cl::desc("Only import first N functions if N>=0 (default -1)"));
+
 static cl::opt<float>
     ImportInstrFactor("import-instr-evolution-factor", cl::init(0.7),
                       cl::Hidden, cl::value_desc("x"),
@@ -276,11 +280,18 @@ static void computeImportForFunction(
     StringMap<FunctionImporter::ExportSetTy> *ExportLists = nullptr) {
   computeImportForReferencedGlobals(Summary, DefinedGVSummaries, ImportList,
                                     ExportLists);
+  static int ImportCount = 0;
   for (auto &Edge : Summary.calls()) {
     ValueInfo VI = Edge.first;
     DEBUG(dbgs() << " edge -> " << VI.getGUID() << " Threshold:" << Threshold
                  << "\n");
 
+    if (ImportCutoff >= 0 && ImportCount >= ImportCutoff) {
+      DEBUG(dbgs() << "ignored! import-cutoff value of " << ImportCutoff
+                   << " reached.\n");
+      continue;
+    }
+
     VI = updateValueInfoForIndirectCalls(Index, VI);
     if (!VI)
       continue;
@@ -343,6 +354,8 @@ static void computeImportForFunction(
     // Mark this function as imported in this module, with the current Threshold
     ProcessedThreshold = AdjThreshold;
 
+    ImportCount++;
+
     // Make exports in the source module.
     if (ExportLists) {
       auto &ExportList = (*ExportLists)[ExportModulePath];