[SystemZ] Prefer LHI;ST... over LAY;MV...

If we had a store of an integer to memory, and the integer and store size
were suitable for a form of MV..., we used MV... no matter what.  We could
then have sequences like:

    lay %r2, 0(%r3,%r4)
    mvi 0(%r2), 4

In these cases it seems better to force the constant into a register
and use a normal store:

    lhi %r2, 4
    stc %r2, 0(%r3, %r4)

since %r2 is more likely to be hoisted and is easier to rematerialize.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189098 91177308-0d34-0410-b5e6-96231b3b80d8
[SystemZ] Try reversing comparisons whose first operand is in memory

This allows us to make more use of the many compare reg,mem instructions.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189099 91177308-0d34-0410-b5e6-96231b3b80d8
[SystemZ] Add basic prefetch support

Just the instructions and intrinsics for now.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189100 91177308-0d34-0410-b5e6-96231b3b80d8
Add function attribute 'optnone'.

This function attribute indicates that the function is not optimized
by any optimization or code generator passes with the 
exception of interprocedural optimization passes.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189101 91177308-0d34-0410-b5e6-96231b3b80d8