R600: Set scheduling preference to Sched::Source

R600 doesn't need to do any scheduling on the SelectionDAG now that it
has a very good MachineScheduler.  Also, using the VLIW SelectionDAG
scheduler was having a major impact on compile times. For example with
the phatk kernel here are the LLVM IR to machine code compile times:

With Sched::VLIW

Total Compile Time:                  1.4890 Seconds (User + System)
SelectionDAG Instruction Scheduling: 1.1670 Seconds (User + System)

With Sched::Source

Total Compile Time:                  0.3330 Seconds (User + System)
SelectionDAG Instruction Scheduling: 0.0070 Seconds (User + System)

The code ouput was identical with both schedulers.  This may not be true
for all programs, but it gives me confidence that there won't be much
reduction, if any, in code quality by using Sched::Source.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188215 91177308-0d34-0410-b5e6-96231b3b80d8
DataFlowSanitizer: fix a use-after-free.  Spotted by libgmalloc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188216 91177308-0d34-0410-b5e6-96231b3b80d8
Reapply r188119 now that the bug it exposed is fixed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188217 91177308-0d34-0410-b5e6-96231b3b80d8
Fix a crash with X86 Mach-O and a subtraction expression where both symbols are
undefined and produce an error message instead as this is a non-relocatable
expression with X86 Mach-O.

rdar://8920876


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188218 91177308-0d34-0410-b5e6-96231b3b80d8
Add some braces, and spaces around operators

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188219 91177308-0d34-0410-b5e6-96231b3b80d8