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Avoid cloning invokes in strength reduction. #4107

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5 changes: 3 additions & 2 deletions xls/passes/strength_reduction_pass.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -50,9 +50,10 @@ namespace {

absl::StatusOr<bool> MaybeSinkOperationIntoSelect(
Node* node, const QueryEngine& query_engine, Select* select_val) {
if (OpIsSideEffecting(node->op())) {
if (OpIsSideEffecting(node->op()) || node->Is<Invoke>()) {
// Side-effecting operations are not always safe to duplicate so don't
// bother.
// bother. Invokes are also excluded because the invoked functions may
// contain side-effecting operations.
return false;
}
DCHECK(!query_engine.IsFullyKnown(select_val));
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26 changes: 26 additions & 0 deletions xls/passes/strength_reduction_pass_test.cc
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Expand Up @@ -503,6 +503,32 @@ TEST_F(StrengthReductionPassTest, DoNotPushDownCheapExtendingOps) {
ASSERT_THAT(Run(f), IsOkAndHolds(false)) << f->DumpIr();
}

TEST_F(StrengthReductionPassTest, DoNotPushDownInvokeThroughSelect) {
auto p = CreatePackage();
Function* callee;
{
FunctionBuilder fb("callee", p.get());
BValue lhs = fb.Param("lhs", p->GetBitsType(32));
BValue rhs = fb.Param("rhs", p->GetBitsType(32));
XLS_ASSERT_OK_AND_ASSIGN(callee, fb.BuildWithReturnValue(fb.Add(lhs, rhs)));
}

FunctionBuilder fb(TestName(), p.get());
BValue selector = fb.Param("selector", p->GetBitsType(1));
BValue rhs = fb.Select(selector, {fb.Literal(UBits(1, 32)),
fb.Literal(UBits(2, 32))});
fb.Invoke({fb.Literal(UBits(3, 32)), rhs}, callee);
XLS_ASSERT_OK_AND_ASSIGN(Function * f, fb.Build());
ASSERT_THAT(Run(f), IsOkAndHolds(false)) << f->DumpIr();

EXPECT_THAT(f->return_value(),
m::Invoke(m::Literal(UBits(3, 32)),
m::Select(m::Param(),
{m::Literal(UBits(1, 32)),
m::Literal(UBits(2, 32))})))
<< f->DumpIr();
}

// This is something we might want to support at some point.
TEST_F(StrengthReductionPassTest, DoNotPushDownMultipleSelects) {
auto p = CreatePackage();
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