[ADT] Fix PR20728 - Incorrect APFloat::fusedMultiplyAdd results for x86_fp80.

As detailed at http://llvm.org/PR20728, due to an internal overflow in
APFloat::multiplySignificand the APFloat::fusedMultiplyAdd method can return
incorrect results for x87DoubleExtended (x86_fp80) values. This commonly
manifests as incorrect constant folding of libm fmal calls on x86. E.g.

fmal(1.0L, 1.0L, 3.0L) == 0.0L      (should be 4.0L)

This patch fixes PR20728 by adding an extra bit to the significand for
intermediate results of APFloat::multiplySignificand, avoiding the overflow.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222374 91177308-0d34-0410-b5e6-96231b3b80d8
[X86] Improved lowering of v4x32 build_vector dag nodes.

This patch improves the lowering of v4f32 and v4i32 build_vector dag nodes
that are known to have at least two non-zero elements.

With this patch, a build_vector that performs a blend with zero is 
converted into a shuffle. This is done to let the shuffle legalizer expand
the dag node in a optimal way. For example, if we know that a build_vector
performs a blend with zero, we can try to lower it as a movq/blend instead of
always selecting an insertps.

This patch also improves the logic that lowers a build_vector into a insertps
with zero masking. See for example the extra test cases added to test sse41.ll.

Differential Revision: http://reviews.llvm.org/D6311


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222375 91177308-0d34-0410-b5e6-96231b3b80d8
AliasSet: Simplify mergeSetIn

No functional change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222376 91177308-0d34-0410-b5e6-96231b3b80d8
Introduce register dump helper

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222379 91177308-0d34-0410-b5e6-96231b3b80d8
MachineVerifier: Report register for bad liveranges

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222380 91177308-0d34-0410-b5e6-96231b3b80d8
Add a print and verify pass after the RegisterCoalescer

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222381 91177308-0d34-0410-b5e6-96231b3b80d8
RegisterCoalescer: Improve debug messages

- Show "Considering..." message after flipping so you actually see the final
  destination vreg as destination.
- Add a message on final join, so you can grep for "Success" messages to obtain
  a list of which register got merged with which.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222382 91177308-0d34-0410-b5e6-96231b3b80d8