[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
diff --git a/clang/lib/Analysis/LiveVariables.cpp b/clang/lib/Analysis/LiveVariables.cpp
index 4f22ccc..afe2d26 100644
--- a/clang/lib/Analysis/LiveVariables.cpp
+++ b/clang/lib/Analysis/LiveVariables.cpp
@@ -93,6 +93,7 @@
LiveVariables::Observer *obs = nullptr);
void dumpBlockLiveness(const SourceManager& M);
+ void dumpStmtLiveness(const SourceManager& M);
LiveVariablesImpl(AnalysisDeclContext &ac, bool KillAtAssign)
: analysisContext(ac),
@@ -327,6 +328,35 @@
// No need to unconditionally visit subexpressions.
return;
}
+ case Stmt::IfStmtClass: {
+ // If one of the branches is an expression rather than a compound
+ // statement, it will be bad if we mark it as live at the terminator
+ // of the if-statement (i.e., immediately after the condition expression).
+ AddLiveStmt(val.liveStmts, LV.SSetFact, cast<IfStmt>(S)->getCond());
+ return;
+ }
+ case Stmt::WhileStmtClass: {
+ // If the loop body is an expression rather than a compound statement,
+ // it will be bad if we mark it as live at the terminator of the loop
+ // (i.e., immediately after the condition expression).
+ AddLiveStmt(val.liveStmts, LV.SSetFact, cast<WhileStmt>(S)->getCond());
+ return;
+ }
+ case Stmt::DoStmtClass: {
+ // If the loop body is an expression rather than a compound statement,
+ // it will be bad if we mark it as live at the terminator of the loop
+ // (i.e., immediately after the condition expression).
+ AddLiveStmt(val.liveStmts, LV.SSetFact, cast<DoStmt>(S)->getCond());
+ return;
+ }
+ case Stmt::ForStmtClass: {
+ // If the loop body is an expression rather than a compound statement,
+ // it will be bad if we mark it as live at the terminator of the loop
+ // (i.e., immediately after the condition expression).
+ AddLiveStmt(val.liveStmts, LV.SSetFact, cast<ForStmt>(S)->getCond());
+ return;
+ }
+
}
for (Stmt *Child : S->children()) {
@@ -632,5 +662,23 @@
llvm::errs() << "\n";
}
+void LiveVariables::dumpStmtLiveness(const SourceManager &M) {
+ getImpl(impl).dumpStmtLiveness(M);
+}
+
+void LiveVariablesImpl::dumpStmtLiveness(const SourceManager &M) {
+ // Don't iterate over blockEndsToLiveness directly because it's not sorted.
+ for (auto I : *analysisContext.getCFG()) {
+
+ llvm::errs() << "\n[ B" << I->getBlockID()
+ << " (live statements at block exit) ]\n";
+ for (auto S : blocksEndToLiveness[I].liveStmts) {
+ llvm::errs() << "\n";
+ S->dump();
+ }
+ llvm::errs() << "\n";
+ }
+}
+
const void *LiveVariables::getTag() { static int x; return &x; }
const void *RelaxedLiveVariables::getTag() { static int x; return &x; }