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backend: reserve registers not preserved across function calls in RISC-V #2853

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Jul 6, 2024
Merged

backend: reserve registers not preserved across function calls in RISC-V #2853

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backend: reserve registers not preserved across function calls in RISC-V
superlopuh Jul 6, 2024
f4b4923
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superlopuh Jul 6, 2024
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15 changes: 15 additions & 0 deletions tests/backend/riscv/test_preallocated.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
from xdsl.backend.riscv.register_allocation import gather_allocated
from xdsl.builder import Builder
from xdsl.dialects import riscv, riscv_func
from xdsl.dialects.builtin import SymbolRefAttr


def test_gather_allocated():
Expand Down Expand Up @@ -56,3 +57,17 @@ def multiple_preallocated_body() -> None:
)

assert len(pa_regs) == 2

@Builder.implicit_region
def func_call_preallocated_body() -> None:
reg1 = riscv.IntRegisterType.unallocated()
v1 = riscv.GetRegisterOp(reg1).res
v2 = riscv.GetRegisterOp(riscv.Registers.S0).res
riscv_func.CallOp(SymbolRefAttr("hello"), (v1, v2), ())

pa_regs = gather_allocated(
riscv_func.FuncOp("foo", func_call_preallocated_body, ((), ()))
)

assert len(pa_regs) == 36
assert riscv.Registers.S0 in pa_regs
11 changes: 10 additions & 1 deletion xdsl/backend/riscv/register_allocation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@
from ordered_set import OrderedSet

from xdsl.backend.riscv.register_queue import RegisterQueue
from xdsl.dialects import riscv_func, riscv_scf, riscv_snitch
from xdsl.dialects import riscv, riscv_func, riscv_scf, riscv_snitch
from xdsl.dialects.riscv import (
FloatRegisterType,
IntRegisterType,
Expand All @@ -26,6 +26,15 @@ def gather_allocated(func: riscv_func.FuncOp) -> set[RISCVRegisterType]:
if not isinstance(op, RISCVAsmOperation):
continue

if isinstance(op, riscv_func.CallOp):
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Probably worth putting a command here as to why this is done for whoever is going to implement call ABI to find and remove this.

# These registers are not guaranteed to hold the same values when the callee
# returns, according to the RISC-V calling convention.
# https://riscv.org/wp-content/uploads/2015/01/riscv-calling.pdf
allocated.update(riscv.Registers.A)
allocated.update(riscv.Registers.T)
allocated.update(riscv.Registers.FA)
allocated.update(riscv.Registers.FT)

for param in chain(op.operands, op.results):
if isinstance(param.type, RISCVRegisterType) and param.type.is_allocated:
if not param.type.register_name.startswith("j"):
Expand Down
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