Preserve branch profile metadata during switch formation.

Preserve branch profile metadata during switch formation.

Patch by Michael Ilseman!
This fixes SimplifyCFGOpt::FoldValueComparisonIntoPredecessors to preserve metata when folding conditional branches into switches.

void foo(int x) {
  if (x == 0)
    bar(1);
  else if (__builtin_expect(x == 10, 1))
    bar(2);
  else if (x == 20)
    bar(3);
}

CFG:

B0
|  \
|   X0
B10
|  \
|   X10
B20
|  \
E   X20

Merge B0-B10:
w(B0-X0) = w(B0-X0)*sum-weights(B10) = w(B0-X0) * (w(B10-X10) + w(B10-B20))
w(B0-X10) = w(B0-B10) * w(B10-X10)
w(B0-B20) = w(B0-B10) * w(B10-B20)

B0 __
| \  \
| X10 X0
B20
|  \
E  X20

Merge B0-B20:
w(B0-X0) = w(B0-X0) * sum-weights(B20) = w(B0-X0) * (w(B20-E) + w(B20-X20))
w(B0-X10) = w(B0-X10) * sum-weights(B20) = ...
w(B0-X20) = w(B0-B20) * w(B20-X20)
w(B0-E) = w(B0-B20) * w(B20-E)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162868 91177308-0d34-0410-b5e6-96231b3b80d8