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[Explicit State Access] Guard State read reference in pipeline_schedule.cc #4564

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Merged
copybara-service merged 1 commit into from
Jul 17, 2026
+31 −1
Merged

[Explicit State Access] Guard State read reference in pipeline_schedule.cc #4564

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3 changes: 2 additions & 1 deletion xls/scheduling/pipeline_schedule.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -207,7 +207,8 @@ bool PipelineSchedule::IsLiveOutOfCycle(Node* node, int64_t c) const {
}
if (user->Is<Next>()) {
Next* user_next = user->As<Next>();
if (user_next->predicate() != node && user_next->value() != node) {
if (user_next->predicate() != node && user_next->value() != node &&
user_next->has_state_read()) {
CHECK_EQ(user_next->state_read(), node);
// This Next node only uses this StateRead node to target the state
// register it needs to write to; it doesn't actually need the value
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29 changes: 29 additions & 0 deletions xls/scheduling/pipeline_schedule_test.cc
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Expand Up @@ -2854,7 +2854,36 @@ TEST_F(PipelineScheduleTest,
EXPECT_EQ(schedule.cycle(next.node()), 1);
EXPECT_EQ(schedule.cycle(read_mutually_exclusive.node()), 2);
}
TEST_F(PipelineScheduleTest, DecoupledNextIsOutOfCycle) {
Package p(TestName());
ProcBuilder pb("the_proc", &p);
XLS_ASSERT_OK_AND_ASSIGN(StateElement * se,
pb.UnreadStateElement("state", Value(UBits(0, 32)),
/*non_synthesizable=*/false));
BValue read = pb.StateRead(se);
BValue next = pb.Next(se, read);
XLS_ASSERT_OK_AND_ASSIGN(Proc * proc, pb.Build());

// Run scheduler to get a valid base schedule first.
SchedulingOptions options;
options.clock_period_ps(1);
options.pipeline_stages(2);
XLS_ASSERT_OK_AND_ASSIGN(
PipelineSchedule schedule,
RunPipelineSchedule(proc, TestDelayEstimator(), options));

ScheduleCycleMap cycle_map = schedule.GetCycleMap();
cycle_map[read.node()] = 0;
cycle_map[next.node()] = 1;
XLS_ASSERT_OK_AND_ASSIGN(schedule, PipelineSchedule::Create(proc, cycle_map));
EXPECT_EQ(schedule.cycle(read.node()), 0);
EXPECT_EQ(schedule.cycle(next.node()), 1);
// Read is consumed by Next in cycle 1, so read IS live out of cycle 0
EXPECT_TRUE(schedule.IsLiveOutOfCycle(read.node(), 0));
// By cycle 1 (where Next is), read no longer requires a pipeline register
// and isn't live out of cycle 1.
EXPECT_FALSE(schedule.IsLiveOutOfCycle(read.node(), 1));
}
TEST_F(PipelineScheduleTest, ProcWriteBeforeReadFailsVerification) {
Package p(TestName());
ProcBuilder pb("the_proc", &p);
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