3 files changed, 55 insertions, 0 deletions
diff --git a/clang/lib/Sema/SemaCXXCast.cpp b/clang/lib/Sema/SemaCXXCast.cpp
index 5753e7bce47..59df294772e 100644
--- a/clang/lib/Sema/SemaCXXCast.cpp
+++ b/clang/lib/Sema/SemaCXXCast.cpp
@@ -468,6 +468,8 @@ CheckReinterpretCast(Sema &Self, Expr *&SrcExpr, QualType DestType,
       != TC_Success && msg != 0)
     Self.Diag(OpRange.getBegin(), msg) << CT_Reinterpret
       << SrcExpr->getType() << DestType << OpRange;
+  else if (Kind == CastExpr::CK_Unknown || Kind == CastExpr::CK_BitCast)
+    Self.CheckCastAlign(SrcExpr, DestType, OpRange);
 }
 
 
@@ -494,6 +496,8 @@ CheckStaticCast(Sema &Self, Expr *&SrcExpr, QualType DestType,
                     Kind, BasePath) != TC_Success && msg != 0)
     Self.Diag(OpRange.getBegin(), msg) << CT_Static
       << SrcExpr->getType() << DestType << OpRange;
+  else if (Kind == CastExpr::CK_Unknown || Kind == CastExpr::CK_BitCast)
+    Self.CheckCastAlign(SrcExpr, DestType, OpRange);
 }
 
 /// TryStaticCast - Check if a static cast can be performed, and do so if
@@ -1303,6 +1307,8 @@ Sema::CXXCheckCStyleCast(SourceRange R, QualType CastTy, Expr *&CastExpr,
   if (tcr != TC_Success && msg != 0)
     Diag(R.getBegin(), msg) << (FunctionalStyle ? CT_Functional : CT_CStyle)
       << CastExpr->getType() << CastTy << R;
+  else if (Kind == CastExpr::CK_Unknown || Kind == CastExpr::CK_BitCast)
+    CheckCastAlign(CastExpr, CastTy, R);
 
   return tcr != TC_Success;
 }
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 7e1eebebdbf..14c0d87ffb7 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -2796,3 +2796,48 @@ bool Sema::CheckParmsForFunctionDef(FunctionDecl *FD) {
 
   return HasInvalidParm;
 }
+
+/// CheckCastAlign - Implements -Wcast-align, which warns when a
+/// pointer cast increases the alignment requirements.
+void Sema::CheckCastAlign(Expr *Op, QualType T, SourceRange TRange) {
+  // This is actually a lot of work to potentially be doing on every
+  // cast; don't do it if we're ignoring -Wcast_align (as is the default).
+  if (getDiagnostics().getDiagnosticLevel(diag::warn_cast_align)
+        == Diagnostic::Ignored)
+    return;
+
+  // Ignore dependent types.
+  if (T->isDependentType() || Op->getType()->isDependentType())
+    return;
+
+  // Require that the destination be a pointer type.
+  const PointerType *DestPtr = T->getAs<PointerType>();
+  if (!DestPtr) return;
+
+  // If the destination has alignment 1, we're done.
+  QualType DestPointee = DestPtr->getPointeeType();
+  if (DestPointee->isIncompleteType()) return;
+  CharUnits DestAlign = Context.getTypeAlignInChars(DestPointee);
+  if (DestAlign.isOne()) return;
+
+  // Require that the source be a pointer type.
+  const PointerType *SrcPtr = Op->getType()->getAs<PointerType>();
+  if (!SrcPtr) return;
+  QualType SrcPointee = SrcPtr->getPointeeType();
+
+  // Whitelist casts from cv void*.  We already implicitly
+  // whitelisted casts to cv void*, since they have alignment 1.
+  // Also whitelist casts involving incomplete types, which implicitly
+  // includes 'void'.
+  if (SrcPointee->isIncompleteType()) return;
+
+  CharUnits SrcAlign = Context.getTypeAlignInChars(SrcPointee);
+  if (SrcAlign >= DestAlign) return;
+
+  Diag(TRange.getBegin(), diag::warn_cast_align)
+    << Op->getType() << T
+    << static_cast<unsigned>(SrcAlign.getQuantity())
+    << static_cast<unsigned>(DestAlign.getQuantity())
+    << TRange << Op->getSourceRange();
+}
+
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 8643dd8386d..f87d39fd8f0 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -3995,6 +3995,10 @@ bool Sema::CheckCastTypes(SourceRange TyR, QualType castType, Expr *&castExpr,
   }
 
   Kind = getScalarCastKind(Context, castExpr->getType(), castType);
+
+  if (Kind == CastExpr::CK_Unknown || Kind == CastExpr::CK_BitCast)
+    CheckCastAlign(castExpr, castType, TyR);
+
   return false;
 }