Under normal circumstances, when a frame pointer is not required, we reserve

Under normal circumstances, when a frame pointer is not required, we reserve
argument space for call sites in the function immediately on entry to the
current function. This eliminates the need for add/sub sp brackets around call
sites. However, this is not always a good idea. If the "call frame" is large and
the target load / store instructions have small immediate field to encode sp
offset, this can cause poor codegen. In the worst case, this can make it
impossible to scavenge a register if the reserved spill slot is pushed too far
apart from sp / fp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36607 91177308-0d34-0410-b5e6-96231b3b80d8