[CFG] [analyzer] Add construction contexts that explain pre-C++17 copy elision.

Before C++17 copy elision was optional, even if the elidable copy/move
constructor had arbitrary side effects. The elidable constructor is present
in the AST, but marked as elidable.

In these cases CFG now contains additional information that allows its clients
to figure out if a temporary object is only being constructed so that to pass
it to an elidable constructor. If so, it includes a reference to the elidable
constructor's construction context, so that the client could elide the
elidable constructor and construct the object directly at its final destination.

Differential Revision: https://reviews.llvm.org/D47616

llvm-svn: 335795

3 files changed, 12 insertions, 1 deletions

diff --git a/clang/lib/StaticAnalyzer/Core/AnalysisManager.cpp b/clang/lib/StaticAnalyzer/Core/AnalysisManager.cpp
index af107ab224f..dc0d3ec8493 100644
--- a/clang/lib/StaticAnalyzer/Core/AnalysisManager.cpp
+++ b/clang/lib/StaticAnalyzer/Core/AnalysisManager.cpp
@@ -31,6 +31,7 @@ AnalysisManager::AnalysisManager(
                 Options.shouldConditionalizeStaticInitializers(),
                 /*addCXXNewAllocator=*/true,
                 Options.includeRichConstructorsInCFG(),
+                Options.shouldElideConstructors(),
                 injector),
       Ctx(ASTCtx), Diags(diags), LangOpts(lang), PathConsumers(PDC),
       CreateStoreMgr(storemgr), CreateConstraintMgr(constraintmgr),
diff --git a/clang/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp b/clang/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp
index bddd4435a75..6fa5fec5288 100644
--- a/clang/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp
+++ b/clang/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp
@@ -321,6 +321,12 @@ bool AnalyzerOptions::shouldSerializeStats() {
                           /* Default = */ false);
 }
 
+bool AnalyzerOptions::shouldElideConstructors() {
+  return getBooleanOption(ElideConstructors,
+                          "elide-constructors",
+                          /* Default = */ true);
+}
+
 int AnalyzerOptions::getOptionAsInteger(StringRef Name, int DefaultVal,
                                         const CheckerBase *C,
                                         bool SearchInParents) {
diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
index f85bfc6e492..497e1fa5560 100644
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
@@ -209,7 +209,11 @@ std::pair<ProgramStateRef, SVal> ExprEngine::prepareForObjectConstruction(
       }
       llvm_unreachable("Unhandled return value construction context!");
     }
-    case ConstructionContext::TemporaryObjectKind: {
+    case ConstructionContext::ElidedTemporaryObjectKind:
+      assert(AMgr.getAnalyzerOptions().shouldElideConstructors());
+      // FALL-THROUGH
+    case ConstructionContext::SimpleTemporaryObjectKind: {
+      // TODO: Copy elision implementation goes here.
       const auto *TCC = cast<TemporaryObjectConstructionContext>(CC);
       const CXXBindTemporaryExpr *BTE = TCC->getCXXBindTemporaryExpr();
       const MaterializeTemporaryExpr *MTE = TCC->getMaterializedTemporaryExpr();