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[SwitchToIf] support multi-result scf.index_switch + add regression test #9245

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Merged
cowardsa merged 2 commits into from
Nov 27, 2025
Merged

[SwitchToIf] support multi-result scf.index_switch + add regression test #9245

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63d3d6e
SwitchToIf: support multi-result scf.index_switch + add regression test
Bynaryman Nov 20, 2025
d7e60df
IndexSwitchToIf: fail if adaptor operand missing
Bynaryman Nov 25, 2025
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17 changes: 10 additions & 7 deletions lib/Transforms/IndexSwitchToIf.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
#include "mlir/IR/OperationSupport.h"
#include "mlir/Pass/Pass.h"
#include "mlir/Transforms/DialectConversion.h"
#include "llvm/ADT/STLExtras.h"

namespace circt {
#define GEN_PASS_DEF_INDEXSWITCHTOIF
Expand All @@ -38,21 +39,23 @@ struct SwitchToIfConversion : public OpConversionPattern<scf::IndexSwitchOp> {
Region &defaultRegion = switchOp.getDefaultRegion();
bool hasResults = !switchOp.getResultTypes().empty();

Value finalResult;
SmallVector<Value> finalResults;
scf::IfOp prevIfOp = nullptr;

rewriter.setInsertionPointAfter(switchOp);
auto switchCases = switchOp.getCases();
Value switchOperand = adaptor.getArg();
if (!switchOperand)
switchOperand = switchOp.getOperand();
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@cowardsa cowardsa Nov 21, 2025

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If getArg fails I would have thought this should be a failure? I.e. return failure(); as then the operator is not satisfying its definition?

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@Bynaryman Bynaryman Nov 25, 2025

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Good catch, I addressed that the simplest possible way @cowardsa

for (size_t i = 0; i < switchCases.size(); i++) {
auto caseValueInt = switchCases[i];
if (prevIfOp)
rewriter.setInsertionPointToStart(&prevIfOp.getElseRegion().front());

Value caseValue =
arith::ConstantIndexOp::create(rewriter, loc, caseValueInt);
Value cond =
arith::CmpIOp::create(rewriter, loc, arith::CmpIPredicate::eq,
switchOp.getOperand(), caseValue);
Value cond = arith::CmpIOp::create(
rewriter, loc, arith::CmpIPredicate::eq, switchOperand, caseValue);

auto ifOp = scf::IfOp::create(rewriter, loc, switchOp.getResultTypes(),
cond, /*hasElseRegion=*/true);
Expand All @@ -70,17 +73,17 @@ struct SwitchToIfConversion : public OpConversionPattern<scf::IndexSwitchOp> {

if (prevIfOp && hasResults) {
rewriter.setInsertionPointToEnd(&prevIfOp.getElseRegion().front());
scf::YieldOp::create(rewriter, loc, ifOp.getResult(0));
scf::YieldOp::create(rewriter, loc, ifOp.getResults());
}

if (i == 0 && hasResults)
finalResult = ifOp.getResult(0);
llvm::append_range(finalResults, ifOp.getResults());

prevIfOp = ifOp;
}

if (hasResults)
rewriter.replaceOp(switchOp, finalResult);
rewriter.replaceOp(switchOp, finalResults);
else
rewriter.eraseOp(switchOp);

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51 changes: 51 additions & 0 deletions test/Transforms/switch-to-if.mlir
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Expand Up @@ -56,6 +56,57 @@ module {
}
}

// Switches that yield multiple values should thread every result through the
// nested if-else chain.

// -----

// CHECK-LABEL: func.func @multi_result(
// CHECK-SAME: %[[ARG:.*]]: index) -> (i32, f32) {
// CHECK: %[[ZERO:.*]] = arith.constant 0 : index
// CHECK: %[[CMP0:.*]] = arith.cmpi eq, %[[ARG]], %[[ZERO]] : index
// CHECK: %[[IF0:[0-9]+]]:2 = scf.if %[[CMP0]] -> (i32, f32) {
// CHECK: %[[C0:.*]] = arith.constant 10 : i32
// CHECK: %[[F0:.*]] = arith.constant 1.000000e+00 : f32
// CHECK: scf.yield %[[C0]], %[[F0]] : i32, f32
// CHECK: } else {
// CHECK: %[[ONE:.*]] = arith.constant 1 : index
// CHECK: %[[CMP1:.*]] = arith.cmpi eq, %[[ARG]], %[[ONE]] : index
// CHECK: %[[IF1:[0-9]+]]:2 = scf.if %[[CMP1]] -> (i32, f32) {
// CHECK: %[[C1:.*]] = arith.constant 20 : i32
// CHECK: %[[F1:.*]] = arith.constant 2.000000e+00 : f32
// CHECK: scf.yield %[[C1]], %[[F1]] : i32, f32
// CHECK: } else {
// CHECK: %[[CDEF:.*]] = arith.constant 30 : i32
// CHECK: %[[FDEF:.*]] = arith.constant 3.000000e+00 : f32
// CHECK: scf.yield %[[CDEF]], %[[FDEF]] : i32, f32
Comment on lines +80 to +82
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@cowardsa cowardsa Nov 21, 2025

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Amusing observation - C default -> CDEF (just thought you'd written a string of letters)

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@Bynaryman Bynaryman Nov 25, 2025

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Just realizing that, Constant of the default case in my mind..

// CHECK: }
// CHECK: scf.yield %[[IF1]]#0, %[[IF1]]#1 : i32, f32
// CHECK: }
// CHECK: return %[[IF0]]#0, %[[IF0]]#1 : i32, f32
// CHECK: }
module {
func.func @multi_result(%arg0 : index) -> (i32, f32) {
%0, %1 = scf.index_switch %arg0 -> i32, f32
case 0 {
%c0 = arith.constant 10 : i32
%f0 = arith.constant 1.0 : f32
scf.yield %c0, %f0 : i32, f32
}
case 1 {
%c1 = arith.constant 20 : i32
%f1 = arith.constant 2.0 : f32
scf.yield %c1, %f1 : i32, f32
}
default {
%cd = arith.constant 30 : i32
%fd = arith.constant 3.0 : f32
scf.yield %cd, %fd : i32, f32
}
return %0, %1 : i32, f32
}
}

// Switch to nested if-else when the yielded result is empty

// -----
Expand Down