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[opt] Support OneHotSelects in our slice-over-select-of-literals optimization #4397

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[opt] Support OneHotSelects in our slice-over-select-of-literals optimization #4397

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3 changes: 3 additions & 0 deletions xls/ir/node_util.h
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Original file line number Diff line number Diff line change
Expand Up @@ -636,6 +636,9 @@ class GenericSelect {
GenericSelect& operator=(const GenericSelect&) = default;
GenericSelect& operator=(GenericSelect&&) = default;
static absl::StatusOr<GenericSelect> From(Node* n);
static bool IsSelect(const Node* n) {
return n->OpIn({Op::kSel, Op::kPrioritySel, Op::kOneHotSel});
}

// Assignment operators from underlying types.
GenericSelect& operator=(Select* select) {
Expand Down
7 changes: 7 additions & 0 deletions xls/passes/BUILD
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Expand Up @@ -1144,9 +1144,15 @@ xls_pass(
hdrs = ["select_lifting_pass.h"],
pass_class = "SelectLiftingPass",
deps = [
":bdd_query_engine",
":critical_path_delay_analysis",
":lazy_ternary_query_engine",
":optimization_pass",
":partial_info_query_engine",
":pass_base",
":query_engine",
":stateless_query_engine",
":union_query_engine",
"//xls/common/status:ret_check",
"//xls/common/status:status_macros",
"//xls/estimators/delay_model:delay_estimator",
Expand Down Expand Up @@ -4602,6 +4608,7 @@ cc_test(
"//xls/ir",
"//xls/ir:bits",
"//xls/ir:function_builder",
"//xls/ir:ir_matcher",
"//xls/ir:ir_test_base",
"//xls/ir:op",
"//xls/solvers:z3_ir_equivalence_testutils",
Expand Down
71 changes: 18 additions & 53 deletions xls/passes/array_simplification_pass.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1381,14 +1381,13 @@ absl::StatusOr<SimplifyResult> SimplifyConditionalAssign(
Node* select, const QueryEngine& query_engine) {
absl::Span<Node* const> original_cases;
std::optional<Node*> original_default_value;
if (select->Is<Select>()) {
original_cases = select->As<Select>()->cases();
original_default_value = select->As<Select>()->default_value();
} else {
XLS_RET_CHECK(select->Is<PrioritySelect>());
original_cases = select->As<PrioritySelect>()->cases();
original_default_value = select->As<PrioritySelect>()->default_value();
XLS_ASSIGN_OR_RETURN(GenericSelect sel, GenericSelect::From(select));
if (select->Is<OneHotSelect>() &&
!query_engine.ExactlyOneBitTrue(sel.selector())) {
return SimplifyResult{.changed = false};
}
original_cases = sel.cases();
original_default_value = sel.default_value();

struct IdentityValue : std::monostate {};
Node* array_to_update = nullptr;
Expand Down Expand Up @@ -1497,24 +1496,9 @@ absl::StatusOr<SimplifyResult> SimplifyConditionalAssign(
}

Node* selected_value;
if (select->Is<Select>()) {
XLS_ASSIGN_OR_RETURN(selected_value,
select->function_base()->MakeNode<Select>(
select->loc(), select->As<Select>()->selector(),
/*cases=*/
case_values,
/*default_value=*/default_value));
} else {
XLS_RET_CHECK(select->Is<PrioritySelect>());
XLS_RET_CHECK(default_value.has_value());
XLS_ASSIGN_OR_RETURN(
selected_value,
select->function_base()->MakeNode<PrioritySelect>(
select->loc(), select->As<PrioritySelect>()->selector(),
/*cases=*/
case_values,
/*default_value=*/*default_value));
}
XLS_ASSIGN_OR_RETURN(
selected_value,
sel.CloneSelectLike(sel.selector(), case_values, default_value));

XLS_ASSIGN_OR_RETURN(
ArrayUpdate * overall_update,
Expand All @@ -1535,16 +1519,9 @@ absl::StatusOr<SimplifyResult> SimplifyConditionalAssign(
// further optimization. On the other hand, this can replicate the select
// logic, which can be expensive in area, so we limit by the number of cases.
absl::StatusOr<SimplifyResult> SimplifySelectOfArrays(Node* select) {
absl::Span<Node* const> original_cases;
std::optional<Node*> original_default_value;
if (select->Is<Select>()) {
original_cases = select->As<Select>()->cases();
original_default_value = select->As<Select>()->default_value();
} else {
XLS_RET_CHECK(select->Is<PrioritySelect>());
original_cases = select->As<PrioritySelect>()->cases();
original_default_value = select->As<PrioritySelect>()->default_value();
}
XLS_ASSIGN_OR_RETURN(GenericSelect sel, GenericSelect::From(select));
absl::Span<Node* const> original_cases = sel.cases();
std::optional<Node*> original_default_value = sel.default_value();

for (Node* sel_case : original_cases) {
if (!sel_case->Is<Array>()) {
Expand Down Expand Up @@ -1578,21 +1555,9 @@ absl::StatusOr<SimplifyResult> SimplifySelectOfArrays(Node* select) {
default_element = original_default_value.value()->operand(i);
}
Node* selected_element;
if (select->Is<Select>()) {
XLS_ASSIGN_OR_RETURN(
selected_element,
select->function_base()->MakeNode<Select>(
select->loc(), select->As<Select>()->selector(),
/*cases=*/elements, /*default=*/default_element));
} else {
XLS_RET_CHECK(select->Is<PrioritySelect>());
XLS_RET_CHECK(default_element.has_value());
XLS_ASSIGN_OR_RETURN(
selected_element,
select->function_base()->MakeNode<PrioritySelect>(
select->loc(), select->As<PrioritySelect>()->selector(),
/*cases=*/elements, /*default=*/*default_element));
}
XLS_ASSIGN_OR_RETURN(
selected_element,
sel.CloneSelectLike(sel.selector(), elements, default_element));
selected_elements.push_back(selected_element);
}
XLS_ASSIGN_OR_RETURN(Array * new_array,
Expand Down Expand Up @@ -1655,7 +1620,7 @@ absl::StatusOr<SimplifyResult> SimplifyArraySlice(
// Simplify various forms of a select of array-typed values.
absl::StatusOr<SimplifyResult> SimplifySelect(Node* select,
const QueryEngine& query_engine) {
XLS_RET_CHECK(select->Is<Select>() || select->Is<PrioritySelect>());
XLS_RET_CHECK(GenericSelect::IsSelect(select));

XLS_ASSIGN_OR_RETURN(SimplifyResult conditional_assign_result,
SimplifyConditionalAssign(select, query_engine));
Expand Down Expand Up @@ -1740,7 +1705,7 @@ absl::StatusOr<bool> ArraySimplificationPass::RunOnFunctionBaseInternal(
for (Node* node : reverse_topo_sort_nodes) {
if (!node->IsDead() &&
node->OpIn({Op::kArray, Op::kArrayIndex, Op::kArrayUpdate, Op::kSel,
Op::kPrioritySel, Op::kArraySlice})) {
Op::kPrioritySel, Op::kOneHotSel, Op::kArraySlice})) {
add_to_worklist(node, false);
}
}
Expand All @@ -1766,7 +1731,7 @@ absl::StatusOr<bool> ArraySimplificationPass::RunOnFunctionBaseInternal(
} else if (node->Is<Array>()) {
XLS_ASSIGN_OR_RETURN(result,
SimplifyArray(node->As<Array>(), query_engine));
} else if (node->Is<Select>() || node->Is<PrioritySelect>()) {
} else if (GenericSelect::IsSelect(node)) {
XLS_ASSIGN_OR_RETURN(result, SimplifySelect(node, query_engine));
} else if (node->Is<ArraySlice>()) {
XLS_ASSIGN_OR_RETURN(
Expand Down
77 changes: 77 additions & 0 deletions xls/passes/array_simplification_pass_test.cc
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Expand Up @@ -1722,6 +1722,83 @@ TEST_F(ArraySimplificationPassTest, IndexOfOneHotSelect) {
m::ArrayIndex(m::Param("b"), {m::Param("i"), m::Param("j")})}));
}

TEST_F(ArraySimplificationPassTest,
SimplifyConditionalAssignWithOneHotSelectAndOneHotSelector) {
Package* p = GetPackage();
FunctionBuilder fb(TestName(), p);
Type* u32 = p->GetBitsType(32);
BValue a_param = fb.Param("a", u32);
BValue b_param = fb.Param("b", u32);
BValue c_param = fb.Param("c", u32);
BValue A = fb.Array({a_param, b_param, c_param}, u32);

BValue x = fb.Param("x", p->GetBitsType(1));
BValue selector = fb.Concat({x, fb.Not(x)});

BValue v = fb.Param("v", u32);
BValue idx = fb.Literal(UBits(1, 32));
BValue A_updated = fb.ArrayUpdate(A, v, {idx});

BValue ohs = fb.OneHotSelect(selector, {A, A_updated});

XLS_ASSERT_OK_AND_ASSIGN(Function * f, fb.BuildWithReturnValue(ohs));
ASSERT_THAT(Run(f), IsOkAndHolds(true));

EXPECT_THAT(
f->return_value(),
m::Array(m::Param("a"),
m::OneHotSelect(m::Concat(m::Param("x"), m::Not(m::Param("x"))),
{m::Param("b"), m::Param("v")}),
m::Param("c")));
}

TEST_F(ArraySimplificationPassTest,
NoSimplifyConditionalAssignWithOneHotSelectAndNonOneHotSelector) {
Package* p = GetPackage();
FunctionBuilder fb(TestName(), p);
Type* u32 = p->GetBitsType(32);
BValue a_param = fb.Param("a", u32);
BValue b_param = fb.Param("b", u32);
BValue c_param = fb.Param("c", u32);
BValue A = fb.Array({a_param, b_param, c_param}, u32);

BValue selector = fb.Param("selector", p->GetBitsType(2));

BValue v = fb.Param("v", u32);
BValue idx = fb.Literal(UBits(1, 32));
BValue A_updated = fb.ArrayUpdate(A, v, {idx});

BValue ohs = fb.OneHotSelect(selector, {A, A_updated});

XLS_ASSERT_OK_AND_ASSIGN(Function * f, fb.BuildWithReturnValue(ohs));
ASSERT_THAT(Run(f), IsOkAndHolds(false));
}

TEST_F(ArraySimplificationPassTest, SimplifySelectOfArraysWithOneHotSelect) {
Package* p = GetPackage();
FunctionBuilder fb(TestName(), p);
Type* u32 = p->GetBitsType(32);
BValue a = fb.Param("a", u32);
BValue b = fb.Param("b", u32);
BValue c = fb.Param("c", u32);
BValue d = fb.Param("d", u32);

BValue A = fb.Array({a, b}, u32);
BValue B = fb.Array({c, d}, u32);

BValue selector = fb.Param("selector", p->GetBitsType(2));
BValue ohs = fb.OneHotSelect(selector, {A, B});

XLS_ASSERT_OK_AND_ASSIGN(Function * f, fb.BuildWithReturnValue(ohs));
ASSERT_THAT(Run(f), IsOkAndHolds(true));

EXPECT_THAT(f->return_value(),
m::Array(m::OneHotSelect(m::Param("selector"),
{m::Param("a"), m::Param("c")}),
m::OneHotSelect(m::Param("selector"),
{m::Param("b"), m::Param("d")})));
}

void IrFuzzArraySimplification(FuzzPackageWithArgs fuzz_package_with_args) {
ArraySimplificationPass pass;
OptimizationPassChangesOutputs(std::move(fuzz_package_with_args), pass);
Expand Down
97 changes: 41 additions & 56 deletions xls/passes/bit_slice_simplification_pass.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -625,27 +625,34 @@ absl::StatusOr<bool> SimplifyLiteralBitSliceUpdate(BitSliceUpdate* update,
return true;
}

bool IsSelectOfLiterals(Node* node, QueryEngine* query_engine) {
bool IsSelectOfLiterals(GenericSelect sel, QueryEngine* query_engine) {
// Only allow OneHotSelect if the selector is actually one-hot.
if (sel.kind() == GenericSelect::Kind::kOneHotSel &&
!query_engine->ExactlyOneBitTrue(sel.selector())) {
return false;
}

auto is_literal_or_select_of_literals = [&](Node* node) {
return query_engine->IsFullyKnown(node) ||
IsSelectOfLiterals(node, query_engine);
if (query_engine->IsFullyKnown(node)) {
return true;
}
if (!GenericSelect::IsSelect(node)) {
return false;
}
absl::StatusOr<GenericSelect> node_sel = GenericSelect::From(node);
CHECK_OK(node_sel);
return IsSelectOfLiterals(*std::move(node_sel), query_engine);
};

if (node->Is<Select>()) {
Select* sel = node->As<Select>();
return sel->AllCases([&](Node* case_value) {
return is_literal_or_select_of_literals(case_value);
});
if (!absl::c_all_of(sel.cases(), [&](Node* case_value) {
return is_literal_or_select_of_literals(case_value);
})) {
return false;
}
if (node->Is<PrioritySelect>()) {
PrioritySelect* sel = node->As<PrioritySelect>();
return absl::c_all_of(sel->cases(),
[&](Node* case_value) {
return is_literal_or_select_of_literals(case_value);
}) &&
is_literal_or_select_of_literals(sel->default_value());
if (sel.default_value().has_value()) {
return is_literal_or_select_of_literals(*sel.default_value());
}
return false;
return true;
}

absl::StatusOr<Node*> LiftThroughSelectsOfLiterals(
Expand All @@ -656,62 +663,36 @@ absl::StatusOr<Node*> LiftThroughSelectsOfLiterals(
return lift_to_literal(*known_value);
}

Node* selector;
absl::Span<Node* const> cases;
std::optional<Node*> default_value;
if (node->Is<Select>()) {
Select* sel = node->As<Select>();
selector = sel->selector();
cases = sel->cases();
default_value = sel->default_value();
} else if (node->Is<PrioritySelect>()) {
PrioritySelect* sel = node->As<PrioritySelect>();
selector = sel->selector();
cases = sel->cases();
default_value = sel->default_value();
} else {
return absl::InternalError(
absl::StrCat("LiftThroughSelectsOfLiterals invoked on a node that was "
"not a select of literals: ",
node->ToString()));
}
XLS_ASSIGN_OR_RETURN(GenericSelect sel, GenericSelect::From(node));

std::vector<Node*> new_cases;
std::optional<Node*> new_default_value = std::nullopt;
new_cases.reserve(cases.size());
for (Node* case_value : cases) {
new_cases.reserve(sel.cases().size());
for (Node* case_value : sel.cases()) {
XLS_ASSIGN_OR_RETURN(Node * new_case_value,
LiftThroughSelectsOfLiterals(case_value, query_engine,
lift_to_literal));
new_cases.push_back(new_case_value);
}
if (default_value.has_value()) {
XLS_ASSIGN_OR_RETURN(new_default_value,
LiftThroughSelectsOfLiterals(
*default_value, query_engine, lift_to_literal));
if (sel.default_value().has_value()) {
XLS_ASSIGN_OR_RETURN(new_default_value, LiftThroughSelectsOfLiterals(
*sel.default_value(),
query_engine, lift_to_literal));
}

if (node->Is<Select>()) {
return node->function_base()->MakeNode<Select>(
node->loc(), selector, new_cases, new_default_value);
}
if (node->Is<PrioritySelect>()) {
XLS_RET_CHECK(new_default_value.has_value());
return node->function_base()->MakeNode<PrioritySelect>(
node->loc(), selector, new_cases, *new_default_value);
}
XLS_RET_CHECK(node->Is<OneHotSelect>());
XLS_RET_CHECK(!new_default_value.has_value());
return node->function_base()->MakeNode<OneHotSelect>(node->loc(), selector,
new_cases);
return sel.CloneSelectLike(sel.selector(), new_cases, new_default_value);
}

// Hoist bit slice updates above selects of literals, where they can be turned
// into static operations.
absl::StatusOr<bool> SimplifySelectOfLiteralsBitSliceUpdate(
BitSliceUpdate* update, QueryEngine* query_engine) {
Node* start = update->start();
if (!IsSelectOfLiterals(start, query_engine)) {
if (!GenericSelect::IsSelect(start)) {
return false;
}
XLS_ASSIGN_OR_RETURN(GenericSelect sel, GenericSelect::From(start));
if (!IsSelectOfLiterals(sel, query_engine)) {
return false;
}

Expand Down Expand Up @@ -822,7 +803,11 @@ absl::StatusOr<bool> SimplifyLiteralDynamicBitSlice(DynamicBitSlice* bit_slice,
absl::StatusOr<bool> SimplifySelectOfLiteralsDynamicBitSlice(
DynamicBitSlice* bit_slice, QueryEngine* query_engine) {
Node* start = bit_slice->start();
if (!IsSelectOfLiterals(start, query_engine)) {
if (!GenericSelect::IsSelect(start)) {
return false;
}
XLS_ASSIGN_OR_RETURN(GenericSelect sel, GenericSelect::From(start));
if (!IsSelectOfLiterals(sel, query_engine)) {
return false;
}

Expand Down
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