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.