Rework CFG edges to encode potentially unreachable edges, instead of just making them NULL.

This is to support some analyses, like -Wunreachable-code, that
will need to recover the original unprunned CFG edges in order
to suppress issues that aren't really bugs in practice.

There are two important changes here:

- AdjacentBlock replaces CFGBlock* for CFG successors/predecessors.
  This has the size of 2 pointers, instead of 1.  This is unlikely
  to have a significant memory impact on Sema since a single
  CFG usually exists at one time, but could impact the memory
  usage of the static analyzer.  This could possibly be optimized
  down to a single pointer with some cleverness.

- Predecessors can now contain null predecessors, which means
  some analyses doing a reverse traversal will need to take into
  account.  This already exists for successors, which contain
  successor slots for specific branch kinds (e.g., 'if') that
  expect a fixed number of successors, even if a branch is
  not reachable.

llvm-svn: 202325

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/Analysis/CFGReachabilityAnalysis.cpp b/clang/lib/Analysis/CFGReachabilityAnalysis.cpp
index 492e66fe817..4ae135f1ea7 100644
--- a/clang/lib/Analysis/CFGReachabilityAnalysis.cpp
+++ b/clang/lib/Analysis/CFGReachabilityAnalysis.cpp
@@ -69,7 +69,8 @@ void CFGReverseBlockReachabilityAnalysis::mapReachability(const CFGBlock *Dst) {
     // Add the predecessors to the worklist.
     for (CFGBlock::const_pred_iterator i = block->pred_begin(), 
          e = block->pred_end(); i != e; ++i) {
-      worklist.push_back(*i);
+      if (*i)
+        worklist.push_back(*i);
     }
   }
 }