[PATCH] D17181: [X86] Don't turn (c?-v:v) into (c?-v:0) by blindly using PSIGN.

[Sanjay Patel via llvm-commits]

spatel added inline comments.

================
Comment at: lib/Target/X86/X86ISelLowering.cpp:26481-26484
@@ +26480,6 @@
+        //   ( M      ? -X : X) == ((X ^   M     ) + (M & 1))
+        // This lets us transform our vselect to:
+        //   (add (xor X, M), (and M, 1))
+        // And further to:
+        //   (add (xor X, M), (srl M, EltBits-1))
+        Mask = DAG.getNode(
----------------
Double-check me to make sure, but we can do one better I think:
((X ^ M) + (M & 1))
((X ^ M) - (M))   <--- since we know that M is all 1s (ie, -1), change the 'add 1' to 'sub -1'


http://reviews.llvm.org/D17181