disable array bounds overflow warning for cases where an array

has a single element.  This disables the warning in cases where
there is a clear bug, but this is really rare (who uses arrays
with one element?) and it also silences a large class of false
positive issues with C89 code that is using tail padding in structs.

A better version of this patch would detect when an array is in
a tail position in a struct, but at least patch fixes the huge
false positives that are hitting postgres and other code.

llvm-svn: 136724

1 files changed, 3 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 28085ef6eab..81ae7b3afb0 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -3491,7 +3491,9 @@ static void CheckArrayAccess_Check(Sema &S,
     else if (size.getBitWidth() < index.getBitWidth())
       size = size.sext(index.getBitWidth());
 
-    if (index.slt(size))
+    // Don't warn for valid indexes, or arrays of size 1 (which are often
+    // tail-allocated arrays that are emulating flexible arrays in C89 code).
+    if (index.slt(size) || size == 1)
       return;
 
     S.DiagRuntimeBehavior(E->getBase()->getLocStart(), BaseExpr,