[PATCH] Make the sqrt intrinsic return undef for a negative input.

[hfinkel at anl.gov]

LGTM.

================
Comment at: lib/Analysis/ConstantFolding.cpp:1527
@@ +1526,3 @@
+            // negative number is not defined for the LLVM sqrt intrinsic.
+            // This is because the intrinsic should only be generated when using
+            // "no-nans-fp-math".
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I'd say, "... should only be emitted in place of a call to libm's sqrt function when using..."

http://reviews.llvm.org/D5527