use -0.0 when creating an fneg instruction

Backends recognize (-0.0 - X) as the canonical form for fneg
and produce better code. Eg, ppc64 with 0.0:

   lis r2, ha16(LCPI0_0)
   lfs f0, lo16(LCPI0_0)(r2)
   fsubs f1, f0, f1
   blr

vs. -0.0:

   fneg f1, f1
   blr

Differential Revision: http://reviews.llvm.org/D6723



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224583 91177308-0d34-0410-b5e6-96231b3b80d8
[ARM] Remove dead assignment.

Found by the Clang static analyzer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224586 91177308-0d34-0410-b5e6-96231b3b80d8
[LoopVectorize] Remove redundant assignment.

Found by the Clang static analyzer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224587 91177308-0d34-0410-b5e6-96231b3b80d8
Reapply: [InstCombine] Fix visitSwitchInst to use right operand types for sub cstexpr

The visitSwitchInst generates SUB constant expressions to recompute the
switch condition. When truncating the condition to a smaller type, SUB
expressions should use the previous type (before trunc) for both
operands. Also, fix code to also return the modified switch when only
the truncation is performed.

This fixes an assertion crash.

Differential Revision: http://reviews.llvm.org/D6644

rdar://problem/19191835

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224588 91177308-0d34-0410-b5e6-96231b3b80d8
[BBVectorize] Remove redundant assignment.

Found by the Clang static analyzer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224589 91177308-0d34-0410-b5e6-96231b3b80d8
[BBVectorize] Remove two more redundant assignments.

Found by the Clang static analyzer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224590 91177308-0d34-0410-b5e6-96231b3b80d8