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back.rtlil: fix expansion of Part() for partial dummy writes.

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Before this commit, selecting a part that was fully out of bounds of
a value was correctly implemented as a write to a dummy wire, but
selecting a part that was only partially out of bounds resulted in
a crash.

Fixes #351.
This commit is contained in:
whitequark 2020-04-13 15:56:39 +00:00
parent edd2bb2c49
commit 814ffde6fb
1 changed files with 8 additions and 6 deletions
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14
nmigen/back/rtlil.py
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@ -632,12 +632,14 @@ class _LHSValueCompiler(_ValueCompiler):
def on_Part(self, value):
offset = self.s.expand(value.offset)
if isinstance(offset, ast.Const):
if offset.value == len(value.value):
dummy_wire = self.s.rtlil.wire(value.width)
return dummy_wire
return self(ast.Slice(value.value,
offset.value * value.stride,
offset.value * value.stride + value.width))
start = offset.value * value.stride
stop = start + value.width
slice = self(ast.Slice(value.value, start, min(len(value.value), stop)))
if len(value.value) >= stop:
return slice
else:
dummy_wire = self.s.rtlil.wire(stop - len(value.value))
return "{{ {} {} }}".format(dummy_wire, slice)
else:
# Only so many possible parts. The amount of branches is exponential; if value.offset
# is large (e.g. 32-bit wide), trying to naively legalize it is likely to exhaust