instead of the frame pointer register:
1) we exactly know the offsets of the temps from the stack pointer
after pass 1 (based on the require parameter stack size for called
routines), while we don't know it for the frame pointer (it depends
on the number of saved registers)
2) temp offsets from the stack pointer are positive while those from
the frame pointer are negative, and we can directly encode much
bigger positive offsets in the instructions
o move the stack pointer register to a virtual register in
loadparentfpn, because many instructions cannot directly operate
on/with the stack pointer
o add the necessary register interference edges for the stack pointer
register
git-svn-id: trunk@29938 -
load a value from a nested context, or to pass a context to a nested
routine. In case a target uses both the stack and frame pointer, this
difference can matter.
git-svn-id: trunk@29937 -
