Fix a bug in the dead stores checker reported in the following email:

  http://lists.cs.uiuc.edu/pipermail/cfe-dev/2008-July/002157.html

Essentially the observer mechanism in LiveVariables was observing block-level
expressions multiple times, leading to a case where the dead store checker could
see a value as dead when it was really live.

llvm-svn: 53115

1 files changed, 11 insertions, 3 deletions

diff --git a/clang/lib/Analysis/LiveVariables.cpp b/clang/lib/Analysis/LiveVariables.cpp
index 54e2195a777..8f391dc5618 100644
--- a/clang/lib/Analysis/LiveVariables.cpp
+++ b/clang/lib/Analysis/LiveVariables.cpp
@@ -133,15 +133,23 @@ public:
 };
       
 void TransferFuncs::Visit(Stmt *S) {
-  if (AD.Observer)
-    AD.Observer->ObserveStmt(S,AD,LiveState);
   
   if (S == getCurrentBlkStmt()) {
+    
+    if (AD.Observer)
+      AD.Observer->ObserveStmt(S,AD,LiveState);
+    
     if (getCFG().isBlkExpr(S)) LiveState(S,AD) = Dead;
     StmtVisitor<TransferFuncs,void>::Visit(S);
   }
-  else if (!getCFG().isBlkExpr(S))
+  else if (!getCFG().isBlkExpr(S)) {
+    
+    if (AD.Observer)
+      AD.Observer->ObserveStmt(S,AD,LiveState);
+    
     StmtVisitor<TransferFuncs,void>::Visit(S);
+    
+  }
   else
     // For block-level expressions, mark that they are live.
     LiveState(S,AD) = Alive;