Index: cfe/trunk/lib/Sema/SemaExpr.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaExpr.cpp
+++ cfe/trunk/lib/Sema/SemaExpr.cpp
@@ -7929,14 +7929,16 @@
       return RHSType;
   }
 
-  // If we're allowing lax vector conversions, only the total (data) size
-  // needs to be the same.
-  // FIXME: Should we really be allowing this?
-  // FIXME: We really just pick the LHS type arbitrarily?
-  if (isLaxVectorConversion(RHSType, LHSType)) {
-    QualType resultType = LHSType;
-    RHS = ImpCastExprToType(RHS.get(), resultType, CK_BitCast);
-    return resultType;
+  // If we're allowing lax vector conversions, only the total (data) size needs
+  // to be the same. If one of the types is scalar, the result is always the
+  // vector type. Don't allow this if the scalar operand is an lvalue.
+  QualType VecType = LHSVecType ? LHSType : RHSType;
+  QualType ScalarType = LHSVecType ? RHSType : LHSType;
+  ExprResult *ScalarExpr = LHSVecType ? &RHS : &LHS;
+  if (isLaxVectorConversion(ScalarType, VecType) &&
+      !ScalarExpr->get()->isLValue()) {
+    *ScalarExpr = ImpCastExprToType(ScalarExpr->get(), VecType, CK_BitCast);
+    return VecType;
   }
 
   // Okay, the expression is invalid.
@@ -9480,7 +9482,7 @@
   }
   
   // Return a signed type for the vector.
-  return GetSignedVectorType(LHSType);
+  return GetSignedVectorType(vType);
 }
 
 QualType Sema::CheckVectorLogicalOperands(ExprResult &LHS, ExprResult &RHS,
Index: cfe/trunk/test/CodeGen/vector.c
===================================================================
--- cfe/trunk/test/CodeGen/vector.c
+++ cfe/trunk/test/CodeGen/vector.c
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple i386-apple-darwin9 -O1 -target-cpu pentium4 -target-feature +sse4.1 -debug-info-kind=limited -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple i386-apple-darwin9 -O1 -target-cpu core2 -debug-info-kind=limited -emit-llvm %s -o - | FileCheck %s
 typedef short __v4hi __attribute__ ((__vector_size__ (8)));
 
 void test1() {
@@ -62,3 +62,23 @@
   extern __typeof(_mm_extract_epi16(_mm_setzero_si128(), 3)) check_result_int;
   extern __typeof(_mm_extract_epi32(_mm_setzero_si128(), 3)) check_result_int;
 }
+
+// Test some logic around our lax vector comparison rules with integers.
+
+typedef int vec_int1 __attribute__((vector_size(4)));
+vec_int1 lax_vector_compare1(int x, vec_int1 y) {
+  y = x == y;
+  return y;
+}
+
+// CHECK: define i32 @lax_vector_compare1(i32 {{.*}}, i32 {{.*}})
+// CHECK: icmp eq <1 x i32>
+
+typedef int vec_int2 __attribute__((vector_size(8)));
+vec_int2 lax_vector_compare2(long long x, vec_int2 y) {
+  y = x == y;
+  return y;
+}
+
+// CHECK: define void @lax_vector_compare2(<2 x i32>* {{.*sret.*}}, i64 {{.*}}, i64 {{.*}})
+// CHECK: icmp eq <2 x i32>
Index: cfe/trunk/test/Sema/vector-cast.c
===================================================================
--- cfe/trunk/test/Sema/vector-cast.c
+++ cfe/trunk/test/Sema/vector-cast.c
@@ -50,7 +50,12 @@
   float2 f2;
   double d;
   f2 += d;
-  d += f2;
+  // We used to allow the next statement, but we've always rejected the next two
+  // statements
+  // FIXME: This diagnostic is inaccurate.
+  d += f2; // expected-error {{cannot convert between vector values of different size}}
+  d = f2; // expected-error {{assigning to 'double' from incompatible type 'float2'}}
+  d = d + f2; // expected-error {{assigning to 'double' from incompatible type 'float2'}}
 }
 
 // rdar://15931426