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

[Ahmed Bougacha via llvm-commits]

ab marked 4 inline comments as done.

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Comment at: lib/Target/X86/X86ISelLowering.cpp:26475-26478
@@ +26474,6 @@
+        // Here, we have a mask, M (all 1s or 0), and, similarly, we know that:
+        //   ((M & 1) ? -X : X) == ((X ^ -(M & 1)) + (M & 1))
+        //   ( M      ? -X : X) == ((X ^   M     ) + (M & 1))
+        // This lets us transform our vselect to:
+        //   (add (xor X, M), (and M, 1))
+        // And further to:
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Ah yes, beautiful!


http://reviews.llvm.org/D17181