2 files changed, 27 insertions, 0 deletions
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index d55ac5ee833..6b20f59046d 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -5562,6 +5562,14 @@ static bool breakDownVectorType(QualType type, uint64_t &len,
 /// vector nor a real type.
 bool Sema::areLaxCompatibleVectorTypes(QualType srcTy, QualType destTy) {
   assert(destTy->isVectorType() || srcTy->isVectorType());
+  
+  // Disallow lax conversions between scalars and ExtVectors (these
+  // conversions are allowed for other vector types because common headers
+  // depend on them).  Most scalar OP ExtVector cases are handled by the
+  // splat path anyway, which does what we want (convert, not bitcast).
+  // What this rules out for ExtVectors is crazy things like char4*float.
+  if (srcTy->isScalarType() && destTy->isExtVectorType()) return false;
+  if (destTy->isScalarType() && srcTy->isExtVectorType()) return false;
 
   uint64_t srcLen, destLen;
   QualType srcElt, destElt;
diff --git a/clang/test/Sema/ext_vector_conversions.c b/clang/test/Sema/ext_vector_conversions.c
new file mode 100644
index 00000000000..aa57e2b17ea
--- /dev/null
+++ b/clang/test/Sema/ext_vector_conversions.c
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macos10.7.0 -fsyntax-only -verify -Wconversion %s
+
+typedef __attribute__((ext_vector_type(4))) char char4;
+typedef __attribute__((ext_vector_type(4))) short short4;
+typedef __attribute__((ext_vector_type(1))) float float1;
+
+static void test() {
+  char4 vc4;
+  float f;
+  // Not allowed.  There's no splatting conversion between float and int vector,
+  // and we don't want to bitcast f to vector-of-char (as would happen with the
+  // old-style vector types).
+  vc4 += f; // expected-error {{cannot convert between vector values of different size}}
+  short4 vs4;
+  long long ll;
+  // This one is OK; we don't re-interpret ll as short4, rather we splat its
+  // value, which should produce a warning about clamping.
+  vs4 += ll; // expected-warning {{implicit conversion loses integer precision}}
+}