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Add .lower() methods to reduction and replication expressions - #9123
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## develop #9123 +/- ##
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| exprt replication_exprt::lower() const | ||
| { | ||
| auto count = numeric_cast_v<std::size_t>(times()); | ||
| exprt::operandst ops; | ||
| ops.reserve(count); | ||
| for(std::size_t i = 0; i < count; i++) | ||
| ops.push_back(op()); | ||
| return concatenation_exprt{std::move(ops), type()}; | ||
| } |
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I believe we want PRECONDITION(count >= 1).
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Verilog does allow zero replications in concatenations; I realise this makes lowering to SMT-LIB a bit harder. I'll add a comment.
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We might just need to fix it on the SMT-LIB output side (which already tries to catch zero-width expressions in some places).
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Add lower() methods to reduction_and_exprt, reduction_nand_exprt, reduction_or_exprt, reduction_nor_exprt, reduction_xor_exprt, reduction_xnor_exprt, and replication_exprt in bitvector_expr.h/cpp. These methods lower high-level bitvector reduction and replication operators to simpler expression forms: - reduction_and(a) → (a = all_ones) - reduction_nand(a) → (a != all_ones) - reduction_or(a) → (a != 0) - reduction_nor(a) → (a = 0) - reduction_xor(a) → a[0] ^ a[1] ^ ... ^ a[n-1] - reduction_xnor(a) → !(a[0] ^ a[1] ^ ... ^ a[n-1]) - replication(n, x) → x :: x :: ... :: x (n times) Use the new .lower() methods in smt2_conv.cpp to replace inline lowering code for reduction_and, reduction_nand, reduction_or, reduction_nor, and reduction_xnor. The reduction_xor case retains its native SMT-LIB encoding using extract + bvxor for efficiency. Co-authored-by: Michael Tautschnig <tautschn@amazon.com>
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Add
lower()methods toreduction_and_exprt,reduction_nand_exprt,reduction_or_exprt,reduction_nor_exprt,reduction_xor_exprt,reduction_xnor_exprt, andreplication_exprtinbitvector_expr.h/bitvector_expr.cpp.These methods lower high-level bitvector reduction and replication operators to simpler expression forms:
reduction_and(a)→(a = all_ones)reduction_nand(a)→(a != all_ones)reduction_or(a)→(a != 0)reduction_nor(a)→(a = 0)reduction_xor(a)→a[0] ^ a[1] ^ ... ^ a[n-1]reduction_xnor(a)→!(a[0] ^ a[1] ^ ... ^ a[n-1])replication(n, x)→x :: x :: ... :: x(n times)Use the new
.lower()methods insmt2_conv.cppto replace inline lowering code forreduction_and,reduction_nand,reduction_or,reduction_nor, andreduction_xnor. Thereduction_xorcase retains its native SMT-LIB encoding usingextract+bvxorfor efficiency.The boolbv layer is not changed since it operates at the propositional literal level, and the SMT2 replication keeps its native
repeatoperator.Companion to diffblue/hw-cbmc#2037 which will use these methods via
.lower()instead of free functions.