For the AAPCS ABI, SP must always be 4-byte aligned, and at any "public
interface" it must be 8-byte aligned.  For the older ARM APCS ABI, the stack
alignment is just always 4 bytes.  For X86, we currently align SP at
entry to a function (e.g., to 16 bytes for Darwin), but no stack alignment
is needed at other times, such as for a leaf function.

After discussing this with Dan, I decided to go with the approach of adding
a new "TransientStackAlignment" field to TargetFrameInfo.  This value
specifies the stack alignment that must be maintained even in between calls.
It defaults to 1 except for ARM, where it is 4.  (Some other targets may
also want to set this if they have similar stack requirements. It's not
currently required for PPC because it sets targetHandlesStackFrameRounding
and handles the alignment in target-specific code.) The existing StackAlignment
value specifies the alignment upon entry to a function, which is how we've
been using it anyway.

llvm-svn: 82767

llvm-svn: 75115

llvm-svn: 45418

llvm-svn: 40589

llvm-svn: 33353

store LR in an arbitrary stack slot
add support for writing varargs functions

llvm-svn: 29876

Remove the hard coded store and load of the link register
Implement ARMFrameInfo

llvm-svn: 29727

redundant after the change.

llvm-svn: 23759

llvm-svn: 23743

llvm-svn: 21425

from PowerPCFrameInfo.h to PowerPCAsmPrinter.cpp where it is actually
needed.

llvm-svn: 17244

llvm-svn: 15929

llvm-svn: 15860

llvm-svn: 15810

allowed).

llvm-svn: 15766

llvm-svn: 15746