another missed SSE optimization

llvm-svn: 39772

lib/Target/X86/README-SSE.txt

@@ -598,3 +598,32 @@ entry:
 }
 
 //===---------------------------------------------------------------------===//
+
+These functions should produce the same code:
+
+#include <emmintrin.h>
+
+typedef long long __m128i __attribute__ ((__vector_size__ (16)));
+
+int foo(__m128i* val) {
+  return __builtin_ia32_vec_ext_v4si(*val, 1);
+}
+int bar(__m128i* val) {
+  union vs {
+    __m128i *_v;
+    int* _s;
+  } v = {val};
+  return v._s[1];
+}
+
+We currently produce (with -m64):
+
+_foo:
+        pshufd $1, (%rdi), %xmm0
+        movd %xmm0, %eax
+        ret
+_bar:
+        movl 4(%rdi), %eax
+        ret
+
+//===---------------------------------------------------------------------===//