AMDGPU: Don't use stack space for SGPR->VGPR spills
Before frame offsets are calculated, try to eliminate the
frame indexes used by SGPR spills. Then we can delete them
after.
I think for now we can be sure that no other instruction
will be re-using the same frame indexes. It should be easy
to notice if this assumption ever breaks since everything
asserts if it tries to use a dead frame index later.
The unused emergency stack slot seems to still be left behind,
so an additional 4 bytes is still wasted.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295753
91177308-0d34-0410-b5e6-
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