[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, 39 insertions, 0 deletions

diff --git a/clang/test/Analysis/use-after-move.cpp b/clang/test/Analysis/use-after-move.cpp
index 18e1b3da6ab..3bb52f164b4 100644
--- a/clang/test/Analysis/use-after-move.cpp
+++ b/clang/test/Analysis/use-after-move.cpp
@@ -778,6 +778,45 @@ void checkLoopZombies() {
   }
 }
 
+void checkMoreLoopZombies1(bool flag) {
+  while (flag) {
+    Empty e{};
+    if (true)
+      e; // expected-warning {{expression result unused}}
+    Empty f = std::move(e); // no-warning
+  }
+}
+
+bool coin();
+
+void checkMoreLoopZombies2(bool flag) {
+  while (flag) {
+    Empty e{};
+    while (coin())
+      e; // expected-warning {{expression result unused}}
+    Empty f = std::move(e); // no-warning
+  }
+}
+
+void checkMoreLoopZombies3(bool flag) {
+  while (flag) {
+    Empty e{};
+    do
+      e; // expected-warning {{expression result unused}}
+    while (coin());
+    Empty f = std::move(e); // no-warning
+  }
+}
+
+void checkMoreLoopZombies4(bool flag) {
+  while (flag) {
+    Empty e{};
+    for (; coin();)
+      e; // expected-warning {{expression result unused}}
+    Empty f = std::move(e); // no-warning
+  }
+}
+
 struct MoveOnlyWithDestructor {
   MoveOnlyWithDestructor();
   ~MoveOnlyWithDestructor();