Add alternate version of LiveVariables analysis that does not kill liveness at assignments. This 'relaxed' liveness is useful in path sensitive analysis for situations where the resulting extended liveness allows us to find some bugs.

- Added killAtAssign flag to LiveVariables
- Added relaxed LiveVariables to AnalysisContext with an accessor

llvm-svn: 112306

1 files changed, 8 insertions, 6 deletions

diff --git a/clang/lib/Analysis/LiveVariables.cpp b/clang/lib/Analysis/LiveVariables.cpp
index 3011fd0dee4..47b2e3d6040 100644
--- a/clang/lib/Analysis/LiveVariables.cpp
+++ b/clang/lib/Analysis/LiveVariables.cpp
@@ -77,12 +77,13 @@ public:
 };
 } // end anonymous namespace
 
-LiveVariables::LiveVariables(AnalysisContext &AC) {  
+LiveVariables::LiveVariables(AnalysisContext &AC, bool killAtAssign) {
   // Register all referenced VarDecls.
   CFG &cfg = *AC.getCFG();
   getAnalysisData().setCFG(cfg);
   getAnalysisData().setContext(AC.getASTContext());
   getAnalysisData().AC = ∾
+  getAnalysisData().killAtAssign = killAtAssign;
 
   RegisterDecls R(getAnalysisData());
   cfg.VisitBlockStmts(R);
@@ -260,12 +261,13 @@ void TransferFuncs::VisitAssign(BinaryOperator* B) {
     if (DR->getDecl()->getType()->isReferenceType()) {
       VisitDeclRefExpr(DR);
     } else {
-      // Update liveness inforamtion.
-      unsigned bit = AD.getIdx(DR->getDecl());
-      LiveState.getDeclBit(bit) = Dead | AD.AlwaysLive.getDeclBit(bit);
-
-      if (AD.Observer) { AD.Observer->ObserverKill(DR); }
+      if (AD.killAtAssign) {
+        // Update liveness inforamtion.
+        unsigned bit = AD.getIdx(DR->getDecl());
+        LiveState.getDeclBit(bit) = Dead | AD.AlwaysLive.getDeclBit(bit);
 
+        if (AD.Observer) { AD.Observer->ObserverKill(DR); }
+      }
       // Handle things like +=, etc., which also generate "uses"
       // of a variable.  Do this just by visiting the subexpression.
       if (B->getOpcode() != BO_Assign)