readme updates

[oota-llvm.git] / lib / Target / PowerPC / README_ALTIVEC.txt

diff --git a/lib/Target/PowerPC/README_ALTIVEC.txt b/lib/Target/PowerPC/README_ALTIVEC.txt
index 143804da07fccb65b75952ea2dbe2b08f99c3339..461b4123c79abe079471889458b3e43a41e3d610 100644 (file)
--- a/lib/Target/PowerPC/README_ALTIVEC.txt
+++ b/lib/Target/PowerPC/README_ALTIVEC.txt
@@ -177,3 +177,12 @@ which prevents the vnot pattern from matching.
 
 
 //===----------------------------------------------------------------------===//
+
+An alternative to the store/store/load approach for illegal insert element 
+lowering would be:
+
+1. store element to any ol' slot
+2. lvx the slot
+3. lvsl 0; splat index; vcmpeq to generate a select mask
+4. lvsl slot + x; vperm to rotate result into correct slot
+5. vsel result together.