R600/SI: Add exec_lo and exec_hi subregisters.

This allows accessing an SReg subregister with a normal subregister
index, instead of getting a machine verifier error.

Also be sure to include all of these subregisters in SReg_32.
This fixes inferring SGPR instead of SReg when finding a
super register class.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214901 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Use register class instead of list of registers

I'm not sure if this has any consequence or not.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214902 91177308-0d34-0410-b5e6-96231b3b80d8
[X86] Improve comments for r214888

A rebase somehow ate my comments. This restores them.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214903 91177308-0d34-0410-b5e6-96231b3b80d8
X86CodeEmitter.cpp: Add SEH_Epilogue to ignored list for legacy JIT, corresponding to r214775.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214905 91177308-0d34-0410-b5e6-96231b3b80d8
Remove dead code in condition

Whether or not it's appropriate, labels have been first-class types
since r51511.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214908 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Fix a crasher due to shuffles which cancel each other out and add
a test case.

We also miscompile this test case which is showing a serious flaw in the
single-input v8i16 shuffle code. I've left the specific instruction
checks FIXME-ed out until I can address the bug in the single-input
code, but I wanted to separate out a significant functionality change to
produce correct code from a very simple and targeted crasher fix.

The miscompile problem stems from keeping track of inputs by value
rather than by index. As a consequence of doing this, we can't reliably
update those inputs because they might swap and we can't detect this
without copying the mask.

The blend code now uses indices for the input lists and this seems
strictly better. It also should make it easier to sort things and do
other cleanups. I think the time has come to simplify The Great Lambda
here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214914 91177308-0d34-0410-b5e6-96231b3b80d8