[analyzer] Fix some expressions staying live too long. Add a debug checker.

StaticAnalyzer uses the CFG-based RelaxedLiveVariables analysis in order to,
in particular, figure out values of which expressions are still needed.
When the expression becomes "dead", it is garbage-collected during
the dead binding scan.

Expressions that constitute branches/bodies of control flow statements,
eg. `E1' in `if (C1) E1;' but not `E2' in `if (C2) { E2; }', were kept alive
for too long. This caused false positives in MoveChecker because it relies
on cleaning up loop-local variables when they go out of scope, but some of those
live-for-too-long expressions were keeping a reference to those variables.

Fix liveness analysis to correctly mark these expressions as dead.

Add a debug checker, debug.DumpLiveStmts, in order to test expressions liveness.

Differential Revision: https://reviews.llvm.org/D55566

llvm-svn: 349320

1 files changed, 19 insertions, 0 deletions

diff --git a/clang/lib/StaticAnalyzer/Checkers/DebugCheckers.cpp b/clang/lib/StaticAnalyzer/Checkers/DebugCheckers.cpp
index 5840ee79133..90b1111aff0 100644
--- a/clang/lib/StaticAnalyzer/Checkers/DebugCheckers.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/DebugCheckers.cpp
@@ -69,6 +69,25 @@ void ento::registerLiveVariablesDumper(CheckerManager &mgr) {
 }
 
 //===----------------------------------------------------------------------===//
+// LiveStatementsDumper
+//===----------------------------------------------------------------------===//
+
+namespace {
+class LiveStatementsDumper : public Checker<check::ASTCodeBody> {
+public:
+  void checkASTCodeBody(const Decl *D, AnalysisManager& Mgr,
+                        BugReporter &BR) const {
+    if (LiveVariables *L = Mgr.getAnalysis<RelaxedLiveVariables>(D))
+      L->dumpStmtLiveness(Mgr.getSourceManager());
+  }
+};
+}
+
+void ento::registerLiveStatementsDumper(CheckerManager &mgr) {
+  mgr.registerChecker<LiveStatementsDumper>();
+}
+
+//===----------------------------------------------------------------------===//
 // CFGViewer
 //===----------------------------------------------------------------------===//