R600/SI: Add load / store machine optimizer pass.

Currently this only functions to match simple cases
where ds_read2_* / ds_write2_* instructions can be used.

In the future it might match some of the other weird
load patterns, such as direct to LDS loads.

Currently enabled only with a subtarget feature to enable
easier testing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219533 91177308-0d34-0410-b5e6-96231b3b80d8
Re-land r219354: Use llvm-symbolizer to symbolize LLVM/Clang crash dumps.

In fact, symbolization is now expected to work only on Linux and
FreeBSD/NetBSD, where we have dl_iterate_phdr and can learn the
main executable name without argv0 (it will be possible on BSD systems
after http://reviews.llvm.org/D5693 lands). #ifdef-out the code for
all the rest Unix systems.

Reviewed in http://reviews.llvm.org/D5610


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219534 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Match read2/write2 stride 64 versions

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219536 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Change how DS offsets are printed

Match SC by using offset/offset0/offset1 and printing
in decimal.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219537 91177308-0d34-0410-b5e6-96231b3b80d8