Optimize those slicing/alias constructions that have no use. (1ed1f0e2) · Commits · ORNL Quantum Computing Institute / qcor

mlir/parsers/qasm3/tests/test_optimization.cpp

+2 −0

Original line number	Diff line number	Diff line
		@@ -380,6 +380,8 @@ cx first_and_last_qubit[0], first_and_last_qubit[1];
		std::cout << "LLVM:\n" << llvm << "\n";
		// Cancel all => No gates, extract, or alloc/dealloc:
		EXPECT_EQ(countSubstring(llvm, "__quantum__qis"), 0);
		// Make sure all runtime (alias construction) functions are removed as well.
		EXPECT_EQ(countSubstring(llvm, "__quantum__"), 0);
		}
		}

mlir/transforms/optimizations/RemoveUnusedQIRCallsPass.cpp

+80 −0

Original line number	Diff line number	Diff line
		@@ -40,6 +40,71 @@ void RemoveUnusedQIRCallsPass::runOnOperation() {
		}
		deadOps.clear();

		// Strategy for alias construction clean-up:
		// In general, we must trim the alias construction from bottom up:
		// i.e. array concatenation (\|\|) must be check (for no use) first then remove
		// if the resulting array is unused. This can then free up the two left and
		// right operands for potential clean-up (by checking for no use).

		// Remove any qubit array concat/create that has no use:
		// (from qubit array aliasing)
		getOperation().walk([&](mlir::quantum::ArrayConcatOp op) {
		// ArrayConcatOp has no use
		if (op.concat_array().use_empty()) {
		deadOps.emplace_back(op.getOperation());
		}
		});
		for (auto &op : deadOps) {
		op->dropAllUses();
		op->erase();
		}
		deadOps.clear();

		getOperation().walk([&](mlir::quantum::ArraySliceOp op) {
		// ArraySliceOp has no use
		if (op.array_slice().use_empty()) {
		deadOps.emplace_back(op.getOperation());
		}
		});
		for (auto &op : deadOps) {
		op->dropAllUses();
		op->erase();
		}
		deadOps.clear();

		// Remove alias array construction that has no use:
		// i.e. createQubitArray then qassign but no other uses:
		getOperation().walk([&](mlir::quantum::QaliasArrayAllocOp op) {
		// QaliasArrayAllocOp has no use except qassign
		// i.e. we construct the alias array but not using it
		bool allUsesAreQassign = true;

		for (auto user_iter = op.qubits().user_begin();
		user_iter != op.qubits().user_end(); ++user_iter) {
		auto user = *user_iter;
		// cast to a AssignQubitOp; break if not a AssignQubitOp
		if (!dyn_cast_or_null<mlir::quantum::AssignQubitOp>(user)) {
		allUsesAreQassign = false;
		break;
		}
		}

		if (allUsesAreQassign) {
		deadOps.emplace_back(op.getOperation());
		for (auto user_iter = op.qubits().user_begin();
		user_iter != op.qubits().user_end(); ++user_iter) {
		auto user = *user_iter;
		auto assignOp = dyn_cast_or_null<mlir::quantum::AssignQubitOp>(user);
		deadOps.emplace_back(assignOp.getOperation());
		}
		}
		});
		for (auto &op : deadOps) {
		op->dropAllUses();
		op->erase();
		}
		deadOps.clear();

		getOperation().walk([&](mlir::quantum::QallocOp op) {
		// QallocOp returns a qubit array, if it
		// only has one user, then that user must be
		@@ -56,5 +121,20 @@ void RemoveUnusedQIRCallsPass::runOnOperation() {
		op->dropAllUses();
		op->erase();
		}
		deadOps.clear();

		// Run another round of ConstantOp trimming
		// (potentially realizable after the above optimizations)
		getOperation().walk([&](mlir::ConstantOp op) {
		// ConstantOp has no use
		if (op.getResult().use_empty()) {
		deadOps.emplace_back(op.getOperation());
		}
		});
		for (auto &op : deadOps) {
		op->dropAllUses();
		op->erase();
		}
		deadOps.clear();
		}
		} // namespace qcor
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