Don't flag idempotent '+' or '-' warnings for pointer arithmetic (typically false positives).

Fixes <rdar://problem/8601243>.

llvm-svn: 117635

2 files changed, 17 insertions, 0 deletions

diff --git a/clang/lib/Checker/IdempotentOperationChecker.cpp b/clang/lib/Checker/IdempotentOperationChecker.cpp
index 3dcbea491eb..7b9ff755a77 100644
--- a/clang/lib/Checker/IdempotentOperationChecker.cpp
+++ b/clang/lib/Checker/IdempotentOperationChecker.cpp
@@ -629,6 +629,13 @@ bool IdempotentOperationChecker::CanVary(const Expr *Ex,
   // The next cases require recursion for subexpressions
   case Stmt::BinaryOperatorClass: {
     const BinaryOperator *B = cast<const BinaryOperator>(Ex);
+
+    // Exclude cases involving pointer arithmetic.  These are usually
+    // false positives.
+    if (B->getOpcode() == BO_Sub || B->getOpcode() == BO_Add)
+      if (B->getLHS()->getType()->getAs<PointerType>())
+        return false;
+
     return CanVary(B->getRHS(), AC)
         || CanVary(B->getLHS(), AC);
    }
diff --git a/clang/test/Analysis/idempotent-operations.c b/clang/test/Analysis/idempotent-operations.c
index c673f0062f0..197357f800e 100644
--- a/clang/test/Analysis/idempotent-operations.c
+++ b/clang/test/Analysis/idempotent-operations.c
@@ -224,3 +224,13 @@ static inline int RDar8431728_C(RDar8431728_D * s, int n,
   return pred;
 }
 
+// <rdar://problem/8601243> - Don't warn on pointer arithmetic.  This
+// is often idiomatic.
+unsigned rdar8601243_aux(unsigned n);
+void rdar8601243() {
+  char arr[100];
+  char *start = arr;
+  start = start + rdar8601243_aux(sizeof(arr) - (arr - start)); // no-warning
+  (void) start;
+}
+