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Use ordered_nodes instead of nodes in mutual exclusion pass. #4939

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Merged
copybara-service merged 1 commit into from
Sep 8, 2026
Merged

Use ordered_nodes instead of nodes in mutual exclusion pass. #4939

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1 change: 1 addition & 0 deletions xls/scheduling/BUILD
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Original file line number Diff line number Diff line change
Expand Up @@ -726,6 +726,7 @@ cc_test(
"//xls/passes:dce_pass",
"//xls/passes:optimization_pass",
"//xls/passes:pass_base",
"//xls/solvers:solver",
"@abseil-cpp//absl/status",
"@abseil-cpp//absl/status:statusor",
"@abseil-cpp//absl/strings",
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4 changes: 2 additions & 2 deletions xls/scheduling/mutual_exclusion_pass.cc
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Expand Up @@ -416,12 +416,12 @@ absl::StatusOr<std::vector<absl::flat_hash_set<Node*>>> ComputeMergeClasses(
scm.at(x) == scm.at(y);
};

for (Node* x : nodes) {
for (Node* x : ordered_nodes) {
if (!(p->GetPredicate(x).has_value())) {
continue;
}
Node* px = p->GetPredicate(x).value();
for (Node* y : nodes) {
for (Node* y : ordered_nodes) {
if (!(p->GetPredicate(y).has_value())) {
continue;
}
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40 changes: 40 additions & 0 deletions xls/scheduling/mutual_exclusion_pass_test.cc
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Expand Up @@ -18,6 +18,7 @@
#include <memory>
#include <optional>
#include <string_view>
#include <variant>

#include "gmock/gmock.h"
#include "gtest/gtest.h"
Expand All @@ -43,6 +44,7 @@
#include "xls/passes/pass_base.h"
#include "xls/scheduling/scheduling_options.h"
#include "xls/scheduling/scheduling_pass.h"
#include "xls/solvers/solver.h"

namespace xls {
namespace {
Expand Down Expand Up @@ -625,6 +627,44 @@ TEST_P(MutualExclusionPassTest, MassiveNumberOfChannelsNoChange) {
EXPECT_EQ(NumberOfOp(proc, Op::kSend), kNumChannels);
}

TEST_P(MutualExclusionPassTest, NonOrderRequestsCauseNonDeterministicResults) {
auto p = std::make_unique<Package>("p");
FunctionBuilder fb("f", p.get());
BValue c = fb.Param("c", p->GetBitsType(1));
BValue x = fb.Param("x", p->GetBitsType(16));
BValue y = fb.Param("y", p->GetBitsType(16));

BValue mul = fb.UMul(x, y);
BValue hard = fb.Eq(mul, fb.Literal(UBits(0x5555, 16)));
BValue c_is_1 = fb.Eq(c, fb.Literal(UBits(1, 1)));
BValue pa = fb.And(c_is_1, hard);
BValue pb = fb.Eq(c, fb.Literal(UBits(0, 1)));

XLS_ASSERT_OK_AND_ASSIGN(Function * f, fb.Build());
XLS_ASSERT_OK_AND_ASSIGN(auto solver,
solvers::CreateSolver(solvers::SolverKind::kZ3));

// At rlimit = 484, proving mutual exclusion in order (pa, pb) succeeds within
// the deterministic resource limit (taking 483 steps), but in reverse order
// (pb, pa) it exhausts the resource limit (requiring 485 steps).
solvers::SolverLimit limit;
limit.deterministic_limit = 484;

auto i1 = solver->CreateSolverInstance(f, /*allow_unsupported=*/true).value();
i1->SetLimit(limit);
auto res1 =
i1->TryProve(pa.node(), solvers::Predicate::IsExclusiveWith(pb.node()));
ASSERT_THAT(res1, absl_testing::IsOk());
EXPECT_TRUE(std::holds_alternative<solvers::ProvenTrue>(*res1));

auto i2 = solver->CreateSolverInstance(f, /*allow_unsupported=*/true).value();
i2->SetLimit(limit);
auto res2 =
i2->TryProve(pb.node(), solvers::Predicate::IsExclusiveWith(pa.node()));
EXPECT_THAT(res2.status(),
absl_testing::StatusIs(absl::StatusCode::kDeadlineExceeded));
}

INSTANTIATE_TEST_SUITE_P(MutualExclusionPassTestSuite, MutualExclusionPassTest,
testing::Values(false, true));

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