Merging r227491:

Merging r227491:
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r227491 | spatel | 2015-01-29 12:51:49 -0800 (Thu, 29 Jan 2015) | 13 lines

[GVN] don't propagate equality comparisons of FP zero (PR22376)

In http://reviews.llvm.org/D6911, we allowed GVN to propagate FP equalities
to allow some simple value range optimizations. But that introduced a bug
when comparing to -0.0 or 0.0: these compare equal even though they are not
bitwise identical.

This patch disallows propagating zero constants in equality comparisons.
Fixes: http://llvm.org/bugs/show_bug.cgi?id=22376
Differential Revision: http://reviews.llvm.org/D7257

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_36@227537 91177308-0d34-0410-b5e6-96231b3b80d8