[llvm-dev] LLVM AArch64 backend using stack pointer to reference local variables

[Momchil Velikov via llvm-dev]

On Fri, Feb 28, 2020 at 6:17 AM Yonghae Kim via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Is there any reasons that the only LLVM AArch64 uses a stack pointer?
>

Using the stack pointer frees up the register, which would have been used
as a frame pointer,
for general allocation.

When accessing the stack frame, offsets from SP are positive, whereas
offsets from a frame
pointer are negative.
When you use SP, you can use LDR with a scaled positive offset, with range
from 0
up to 16380 (or 32760 for 64-bit accesses).
If you use FP, you would use, LDUR with a negative offset, with a range
just [-256, 255].

What downsides of using SP do you see?

~chill
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