[analyzer] Add analyzer option to limit the number of imported TUs

Summary:
During CTU analysis of complex projects, the loaded AST-contents of
imported TUs can grow bigger than available system memory. This option
introduces a threshold on the number of TUs to be imported for a single
TU in order to prevent such cases.

Differential Revision: https://reviews.llvm.org/D59798

llvm-svn: 365314

clang/include/clang/CrossTU/CrossTranslationUnit.h

@@ -45,7 +45,8 @@ enum class index_error_code {
   failed_to_generate_usr,
   triple_mismatch,
   lang_mismatch,
-  lang_dialect_mismatch
+  lang_dialect_mismatch,
+  load_threshold_reached
 };
 
 class IndexError : public llvm::ErrorInfo<IndexError> {
@@ -134,7 +135,8 @@ class CrossTranslationUnitContext {
   /// A definition with the same declaration will be looked up in the
   /// index file which should be in the \p CrossTUDir directory, called
   /// \p IndexName. In case the declaration is found in the index the
-  /// corresponding AST file will be loaded.
+  /// corresponding AST file will be loaded. If the number of TUs imported
+  /// reaches \p CTULoadTreshold, no loading is performed.
   ///
   /// \return Returns a pointer to the ASTUnit that contains the definition of
   /// the looked up name or an Error.
@@ -182,6 +184,10 @@ class CrossTranslationUnitContext {
   CompilerInstance &CI;
   ASTContext &Context;
   std::shared_ptr<ASTImporterSharedState> ImporterSharedSt;
+  /// \p CTULoadTreshold should serve as an upper limit to the number of TUs
+  /// imported in order to reduce the memory footprint of CTU analysis.
+  const unsigned CTULoadThreshold;
+  unsigned NumASTLoaded{0u};
 };
 
 } // namespace cross_tu

clang/include/clang/StaticAnalyzer/Core/AnalyzerOptions.def

@@ -300,6 +300,14 @@ ANALYZER_OPTION(bool, ShouldTrackConditionsDebug, "track-conditions-debug",
                 "Whether to place an event at each tracked condition.",
                 false)
 
+ANALYZER_OPTION(unsigned, CTUImportThreshold, "ctu-import-threshold",
+                "The maximal amount of translation units that is considered "
+                "for import when inlining functions during CTU analysis. "
+                "Lowering this threshold can alleviate the memory burder of "
+                "analysis with many interdependent definitions located in "
+                "various translation units.",
+                100u)
+
 //===----------------------------------------------------------------------===//
 // Unsinged analyzer options.
 //===----------------------------------------------------------------------===//

clang/lib/CrossTU/CrossTranslationUnit.cpp

@@ -47,6 +47,8 @@ STATISTIC(NumNameConflicts, "The # of imports when the ASTImporter "
 STATISTIC(NumTripleMismatch, "The # of triple mismatches");
 STATISTIC(NumLangMismatch, "The # of language mismatches");
 STATISTIC(NumLangDialectMismatch, "The # of language dialect mismatches");
+STATISTIC(NumASTLoadThresholdReached,
+          "The # of ASTs not loaded because of threshold");
 
 // Same as Triple's equality operator, but we check a field only if that is
 // known in both instances.
@@ -106,6 +108,8 @@ class IndexErrorCategory : public std::error_category {
       return "Language mismatch";
     case index_error_code::lang_dialect_mismatch:
       return "Language dialect mismatch";
+    case index_error_code::load_threshold_reached:
+      return "Load threshold reached";
     }
     llvm_unreachable("Unrecognized index_error_code.");
   }
@@ -184,7 +188,8 @@ template <typename T> static bool hasBodyOrInit(const T *D) {
 }
 
 CrossTranslationUnitContext::CrossTranslationUnitContext(CompilerInstance &CI)
-    : CI(CI), Context(CI.getASTContext()) {}
+    : CI(CI), Context(CI.getASTContext()),
+      CTULoadThreshold(CI.getAnalyzerOpts()->CTUImportThreshold) {}
 
 CrossTranslationUnitContext::~CrossTranslationUnitContext() {}
 
@@ -232,8 +237,8 @@ llvm::Expected<const T *> CrossTranslationUnitContext::getCrossTUDefinitionImpl(
   if (LookupName.empty())
     return llvm::make_error<IndexError>(
         index_error_code::failed_to_generate_usr);
-  llvm::Expected<ASTUnit *> ASTUnitOrError =
-      loadExternalAST(LookupName, CrossTUDir, IndexName, DisplayCTUProgress);
+  llvm::Expected<ASTUnit *> ASTUnitOrError = loadExternalAST(
+      LookupName, CrossTUDir, IndexName, DisplayCTUProgress);
   if (!ASTUnitOrError)
     return ASTUnitOrError.takeError();
   ASTUnit *Unit = *ASTUnitOrError;
@@ -342,6 +347,13 @@ llvm::Expected<ASTUnit *> CrossTranslationUnitContext::loadExternalAST(
   //        a lookup name from a single translation unit. If multiple
   //        translation units contains decls with the same lookup name an
   //        error will be returned.
+
+  if (NumASTLoaded >= CTULoadThreshold) {
+    ++NumASTLoadThresholdReached;
+    return llvm::make_error<IndexError>(
+        index_error_code::load_threshold_reached);
+  }
+
   ASTUnit *Unit = nullptr;
   auto NameUnitCacheEntry = NameASTUnitMap.find(LookupName);
   if (NameUnitCacheEntry == NameASTUnitMap.end()) {
@@ -379,6 +391,7 @@ llvm::Expected<ASTUnit *> CrossTranslationUnitContext::loadExternalAST(
           ASTUnit::LoadEverything, Diags, CI.getFileSystemOpts()));
       Unit = LoadedUnit.get();
       FileASTUnitMap[ASTFileName] = std::move(LoadedUnit);
+      ++NumASTLoaded;
       if (DisplayCTUProgress) {
         llvm::errs() << "CTU loaded AST file: "
                      << ASTFileName << "\n";

clang/test/Analysis/analyzer-config.c

@@ -27,6 +27,7 @@
 // CHECK-NEXT: cplusplus.Move:WarnOn = KnownsAndLocals
 // CHECK-NEXT: crosscheck-with-z3 = false
 // CHECK-NEXT: ctu-dir = ""
+// CHECK-NEXT: ctu-import-threshold = 100
 // CHECK-NEXT: ctu-index-name = externalDefMap.txt
 // CHECK-NEXT: debug.AnalysisOrder:* = false
 // CHECK-NEXT: debug.AnalysisOrder:Bind = false
@@ -90,4 +91,4 @@
 // CHECK-NEXT: unroll-loops = false
 // CHECK-NEXT: widen-loops = false
 // CHECK-NEXT: [stats]
-// CHECK-NEXT: num-entries = 87
+// CHECK-NEXT: num-entries = 88

clang/test/Analysis/ctu-import-threshold.c

@@ -0,0 +1,5 @@
+// Ensure analyzer option 'ctu-import-threshold' is a recognized option.
+//
+// RUN: %clang_cc1 -analyze -analyzer-config ctu-import-threshold=30 -verify %s
+//
+// expected-no-diagnostics

clang/unittests/CrossTU/CrossTranslationUnitTest.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/CrossTU/CrossTranslationUnit.h"
+#include "clang/Frontend/CompilerInstance.h"
 #include "clang/AST/ASTConsumer.h"
 #include "clang/Frontend/FrontendAction.h"
 #include "clang/Tooling/Tooling.h"
@@ -70,12 +71,14 @@ class CTUASTConsumer : public clang::ASTConsumer {
     EXPECT_TRUE(llvm::sys::fs::exists(ASTFileName));
 
     // Load the definition from the AST file.
-    llvm::Expected<const FunctionDecl *> NewFDorError =
-        CTU.getCrossTUDefinition(FD, "", IndexFileName);
-    EXPECT_TRUE((bool)NewFDorError);
-    const FunctionDecl *NewFD = *NewFDorError;
+    llvm::Expected<const FunctionDecl *> NewFDorError = handleExpected(
+        CTU.getCrossTUDefinition(FD, "", IndexFileName, false),
+        []() { return nullptr; }, [](IndexError &) {});
 
-    *Success = NewFD && NewFD->hasBody() && !OrigFDHasBody;
+    if (NewFDorError) {
+      const FunctionDecl *NewFD = *NewFDorError;
+      *Success = NewFD && NewFD->hasBody() && !OrigFDHasBody;
+    }
   }
 
 private:
@@ -85,26 +88,37 @@ class CTUASTConsumer : public clang::ASTConsumer {
 
 class CTUAction : public clang::ASTFrontendAction {
 public:
-  CTUAction(bool *Success) : Success(Success) {}
+  CTUAction(bool *Success, unsigned OverrideLimit)
+      : Success(Success), OverrideLimit(OverrideLimit) {}
 
 protected:
   std::unique_ptr<clang::ASTConsumer>
   CreateASTConsumer(clang::CompilerInstance &CI, StringRef) override {
+    CI.getAnalyzerOpts()->CTUImportThreshold = OverrideLimit;
     return llvm::make_unique<CTUASTConsumer>(CI, Success);
   }
 
 private:
   bool *Success;
+  const unsigned OverrideLimit;
 };
 
 } // end namespace
 
 TEST(CrossTranslationUnit, CanLoadFunctionDefinition) {
   bool Success = false;
-  EXPECT_TRUE(tooling::runToolOnCode(new CTUAction(&Success), "int f(int);"));
+  EXPECT_TRUE(
+      tooling::runToolOnCode(new CTUAction(&Success, 1u), "int f(int);"));
   EXPECT_TRUE(Success);
 }
 
+TEST(CrossTranslationUnit, RespectsLoadThreshold) {
+  bool Success = false;
+  EXPECT_TRUE(
+      tooling::runToolOnCode(new CTUAction(&Success, 0u), "int f(int);"));
+  EXPECT_FALSE(Success);
+}
+
 TEST(CrossTranslationUnit, IndexFormatCanBeParsed) {
   llvm::StringMap<std::string> Index;
   Index["a"] = "/b/f1";