Another entry about shuffles.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27245 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index 09d9bb6ef866f5ce88bae47ab6fe708886dd18e8..060552b93deeab8aecf27260e6099bec9a9e1eb6 100644 (file)
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -667,3 +667,9 @@ directly %esp[0] if there are no other uses.
 
 Use movhps to update upper 64-bits of a v4sf value. Also movlps on lower half
 of a v4sf value.
+
+//===---------------------------------------------------------------------===//
+
+Better codegen for vector_shuffles like this { x, 0, 0, 0 } or { x, 0, x, 0}.
+Perhaps use pxor / xorp* to clear a XMM register first?
+