PNaCl SIMD documentation: fix vector-scalar examples, currently unsupported by LLVM

R= dschuff@chromium.org
TEST= none
BUG= https://code.google.com/p/nativeclient/issues/detail?id=2205
NOTRY=true
(documentation only change)

Review URL: https://codereview.chromium.org/293093004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272339 0039d316-1c4b-4281-b951-d872f2087c98

native_client_sdk/doc_generated/reference/pnacl-c-cpp-language-support.html

@@ -211,9 +211,8 @@ typedef int v4s __attribute__((vector_size(VECTOR_BYTES)));
 v4s a = {1,2,3,4};
 v4s b = {5,6,7,8};
 v4s c, d, e;
-c = b + 1;  /* c = b + {1,1,1,1}; */
-d = 2 * b;  /* d = {2,2,2,2} * b; */
-e = c + d;
+c = a + b;  /* c = {6,8,10,12} */
+d = b >> a; /* d = {2,1,0,0} */
 </pre>
 <p>Vector comparisons are represented as a bitmask as wide as the compared
 elements of all <code>0</code> or all <code>1</code>:</p>
@@ -334,21 +333,30 @@ to the number of indices specified.</p>
 // identity operation - return 4-element vector v1.
 __builtin_shufflevector(v1, v1, 0, 1, 2, 3)
 
-// &quot;Splat&quot; element 0 of V1 into a 4-element result.
-__builtin_shufflevector(V1, V1, 0, 0, 0, 0)
+// &quot;Splat&quot; element 0 of v1 into a 4-element result.
+__builtin_shufflevector(v1, v1, 0, 0, 0, 0)
 
-// Reverse 4-element vector V1.
-__builtin_shufflevector(V1, V1, 3, 2, 1, 0)
+// Reverse 4-element vector v1.
+__builtin_shufflevector(v1, v1, 3, 2, 1, 0)
 
-// Concatenate every other element of 4-element vectors V1 and V2.
-__builtin_shufflevector(V1, V2, 0, 2, 4, 6)
+// Concatenate every other element of 4-element vectors v1 and v2.
+__builtin_shufflevector(v1, v2, 0, 2, 4, 6)
 
-// Concatenate every other element of 8-element vectors V1 and V2.
-__builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
+// Concatenate every other element of 8-element vectors v1 and v2.
+__builtin_shufflevector(v1, v2, 0, 2, 4, 6, 8, 10, 12, 14)
 
 // Shuffle v1 with some elements being undefined
 __builtin_shufflevector(v1, v1, 3, -1, 1, -1)
 </pre>
+<p>One common use of <code>__builtin_shufflevector</code> is to perform
+vector-scalar operations:</p>
+<pre class="prettyprint">
+typedef int v4s __attribute__((vector_size(16)));
+v4s shift_right_by(v4s shift_me, int shift_amount) {
+  v4s tmp = {shift_amount};
+  return shift_me &gt;&gt; __builtin_shuffle_vector(tmp, tmp, 0, 0, 0, 0);
+}
+</pre>
 </section><section id="auto-vectorization">
 <h3 id="auto-vectorization">Auto-Vectorization</h3>
 <p>Auto-vectorization is currently not enabled for Portable Native Client,

native_client_sdk/src/doc/reference/pnacl-c-cpp-language-support.rst

@@ -236,9 +236,8 @@ Vector types can be used through the ``vector_size`` attribute:
   v4s a = {1,2,3,4};
   v4s b = {5,6,7,8};
   v4s c, d, e;
-  c = b + 1;  /* c = b + {1,1,1,1}; */
-  d = 2 * b;  /* d = {2,2,2,2} * b; */
-  e = c + d;
+  c = a + b;  /* c = {6,8,10,12} */
+  d = b >> a; /* d = {2,1,0,0} */
 
 Vector comparisons are represented as a bitmask as wide as the compared
 elements of all ``0`` or all ``1``:
@@ -339,21 +338,32 @@ to the number of indices specified.
   // identity operation - return 4-element vector v1.
   __builtin_shufflevector(v1, v1, 0, 1, 2, 3)
 
-  // "Splat" element 0 of V1 into a 4-element result.
-  __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
+  // "Splat" element 0 of v1 into a 4-element result.
+  __builtin_shufflevector(v1, v1, 0, 0, 0, 0)
 
-  // Reverse 4-element vector V1.
-  __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
+  // Reverse 4-element vector v1.
+  __builtin_shufflevector(v1, v1, 3, 2, 1, 0)
 
-  // Concatenate every other element of 4-element vectors V1 and V2.
-  __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
+  // Concatenate every other element of 4-element vectors v1 and v2.
+  __builtin_shufflevector(v1, v2, 0, 2, 4, 6)
 
-  // Concatenate every other element of 8-element vectors V1 and V2.
-  __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
+  // Concatenate every other element of 8-element vectors v1 and v2.
+  __builtin_shufflevector(v1, v2, 0, 2, 4, 6, 8, 10, 12, 14)
 
   // Shuffle v1 with some elements being undefined
   __builtin_shufflevector(v1, v1, 3, -1, 1, -1)
 
+One common use of ``__builtin_shufflevector`` is to perform
+vector-scalar operations:
+
+.. naclcode::
+
+  typedef int v4s __attribute__((vector_size(16)));
+  v4s shift_right_by(v4s shift_me, int shift_amount) {
+    v4s tmp = {shift_amount};
+    return shift_me >> __builtin_shuffle_vector(tmp, tmp, 0, 0, 0, 0);
+  }
+
 Auto-Vectorization
 ------------------