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opt_expr: only sign extend shift arguments for arithmetic right shift

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This commit is contained in:
George Rennie 2025-04-26 12:03:50 +02:00
parent 2d6255175e
commit c952ab417f
1 changed files with 5 additions and 4 deletions
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9
passes/opt/opt_expr.cc
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@ -1315,13 +1315,14 @@ skip_fine_alu:
RTLIL::SigSpec sig_a = assign_map(cell->getPort(ID::A));
RTLIL::SigSpec sig_y(cell->type == ID($shiftx) ? RTLIL::State::Sx : RTLIL::State::S0, cell->getParam(ID::Y_WIDTH).as_int());
// Limit indexing to the size of a, which is behaviourally identical (result is all 0)
// and avoids integer overflow of i + shift_bits when e.g. ID::B == INT_MAX
shift_bits = min(shift_bits, GetSize(sig_a));
if (cell->type != ID($shiftx) && GetSize(sig_a) < GetSize(sig_y))
sig_a.extend_u0(GetSize(sig_y), cell->getParam(ID::A_SIGNED).as_bool());
// Limit indexing to the size of a, which is behaviourally identical (result is all 0)
// and avoids integer overflow of i + shift_bits when e.g. ID::B == INT_MAX.
// We do this after sign-extending a so this accounts for the output size
shift_bits = min(shift_bits, GetSize(sig_a));
for (int i = 0; i < GetSize(sig_y); i++) {
int idx = i + shift_bits;
if (0 <= idx && idx < GetSize(sig_a))