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[circt-bmc] Add dbg.trace for BMC counterexample value tracking #10747

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[circt-bmc] Add dbg.trace for BMC counterexample value tracking #10747

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17 changes: 17 additions & 0 deletions include/circt/Dialect/Debug/DebugOps.td
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Original file line number Diff line number Diff line change
Expand Up @@ -82,6 +82,23 @@ def VariableOp : DebugOp<"variable"> {
}];
}

def TraceOp : DebugOp<"trace"> {

@TaoBi22 TaoBi22 Jul 1, 2026

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I'm not totally sure having this in the debug dialect is the right move when it's very specific to BMC. Maybe the verif dialect would make more sense?

let summary = "Record a named runtime value for counterexample tracing";
let description = [{
Records a named value at a specific step for later counterexample
materialization. This is intended as an internal bridge from the BMC flow
to the final runtime-backed text/VCD emission path.

@TaoBi22 TaoBi22 Jul 1, 2026

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I'm not sure the motivation for this op is entirely clear to me; what's the aim for its eventual lowering?

Would the aim be to lower this op to some call that reaches out to the BMCTrace runtime with a value and a cycle number? If that's the case then I'm not sure it's completely clear to me why we need a dedicated op for this instead of building this IR directly as we build the for loop that it sits in.

@5iri 5iri Jul 5, 2026

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The intended lowering is a later counterexample-materialization step that consumes dbg.trace(step, name, value) and lowers it to the BMC runtime trace path. I introduced a dedicated op to keep VerifToSMT backend-neutral instead of constructing runtime-specific IR directly in the loop body. You’re right that this isn’t clear from the current patch.

}];
let arguments = (ins
I32:$step,
StrAttr:$name,
AnyType:$value
);
let assemblyFormat = [{
$step `,` $name `,` $value attr-dict `:` type($step) `,` type($value)
}];
}


def ValueOp : DebugOp<"value"> {
let summary = "Attach source-language metadata to a value";
Expand Down
16 changes: 15 additions & 1 deletion lib/Conversion/SMTToZ3LLVM/LowerSMTToZ3LLVM.cpp
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Expand Up @@ -1282,6 +1282,18 @@ struct IntAbsOpLowering : public SMTLoweringPattern<IntAbsOp> {
// For now we want to ignore Debug variable and scope ops - eventually we'll
// give this debug info to Z3

/// Strip dbg.trace ops.
struct DbgTraceLowering : public OpConversionPattern<debug::TraceOp> {
using OpConversionPattern::OpConversionPattern;

LogicalResult
matchAndRewrite(debug::TraceOp op, OpAdaptor adaptor,
ConversionPatternRewriter &rewriter) const final {
rewriter.eraseOp(op);
return success();
}
};

/// Strip dbg.variable ops.
struct DbgVariableLowering : public OpConversionPattern<debug::VariableOp> {
using OpConversionPattern::OpConversionPattern;
Expand Down Expand Up @@ -1546,7 +1558,9 @@ void circt::populateSMTToZ3LLVMConversionPatterns(
BV2IntOpLowering, QuantifierLowering<ForallOp>,
QuantifierLowering<ExistsOp>>(converter, patterns.getContext(),
globals, options);
patterns.add<DbgVariableLowering, DbgScopeLowering>(patterns.getContext());
patterns.add<DbgTraceLowering>(patterns.getContext());
patterns.add<DbgVariableLowering>(patterns.getContext());
patterns.add<DbgScopeLowering>(patterns.getContext());
}

void LowerSMTToZ3LLVMPass::runOnOperation() {
Expand Down
17 changes: 17 additions & 0 deletions lib/Conversion/VerifToSMT/VerifToSMT.cpp
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Expand Up @@ -70,6 +70,20 @@ static void attachDebugVariables(
}
}

static void attachTraceRecords(
OpBuilder &builder, Location loc, Value step, ArrayRef<Type> originalTypes,
ValueRange values,
const llvm::SmallDenseMap<unsigned, StringAttr> &debugNames) {
for (auto [argIndex, value] : llvm::enumerate(values)) {
if (isa<seq::ClockType>(originalTypes[argIndex]))
continue;
auto it = debugNames.find(argIndex);
if (it == debugNames.end())
continue;
debug::TraceOp::create(builder, loc, step, it->second, value);
}
}

/// Lower a verif::AssertOp operation with an i1 operand to a smt::AssertOp,
/// negated to check for unsatisfiability.
struct VerifAssertOpConversion : OpConversionPattern<verif::AssertOp> {
Expand Down Expand Up @@ -559,6 +573,9 @@ struct VerifBoundedModelCheckingOpConversion
attachDebugVariables(
builder, loc, oldCircuitInputTy,
iterArgs.take_front(circuitFuncOp.getNumArguments()), debugNames);
attachTraceRecords(
builder, loc, i, oldCircuitInputTy,
iterArgs.take_front(circuitFuncOp.getNumArguments()), debugNames);

// Drop existing assertions
smt::PopOp::create(builder, loc, 1);
Expand Down
3 changes: 3 additions & 0 deletions test/Conversion/SMTToZ3LLVM/smt-to-z3-llvm.mlir
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Expand Up @@ -391,6 +391,9 @@ func.func @test(%arg0: i32) {
// CHECK: llvm.call @Z3_mk_bv2int({{%[0-9a-zA-Z_]+}}, [[BV0]], [[SIGNEDCONST]]) : (!llvm.ptr, !llvm.ptr, i1) -> !llvm.ptr
smt.bv2int %c0_bv4 signed : !smt.bv<4>

// CHECK-NOT: dbg.trace
dbg.trace %arg1, "var0", %c0_bv4 : i32, !smt.bv<4>

// CHECK-NOT: dbg.variable
dbg.variable "var1", %c0_bv4 : !smt.bv<4>

Expand Down
4 changes: 3 additions & 1 deletion test/Conversion/VerifToSMT/bmc-debug-names.mlir
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Expand Up @@ -5,9 +5,11 @@
// CHECK: [[REG_DECL:%.+]] = smt.declare_fun "state_q" : !smt.bv<8>
// CHECK: dbg.variable "data_in", [[INPUT_DECL]] : !smt.bv<8>
// CHECK: dbg.variable "state_q", [[REG_DECL]] : !smt.bv<8>
// CHECK: scf.for {{%.+}} iter_args([[CLK_ARG:%.+]] = {{%.+}}, [[INPUT_ARG:%.+]] = [[INPUT_DECL]], [[REG_ARG:%.+]] = [[REG_DECL]], {{%.+}})
// CHECK: scf.for [[STEP:%.+]] = {{%.+}} iter_args([[CLK_ARG:%.+]] = {{%.+}}, [[INPUT_ARG:%.+]] = [[INPUT_DECL]], [[REG_ARG:%.+]] = [[REG_DECL]], {{%.+}})
// CHECK: dbg.variable "data_in", [[INPUT_ARG]] : !smt.bv<8>
// CHECK: dbg.variable "state_q", [[REG_ARG]] : !smt.bv<8>
// CHECK: dbg.trace [[STEP]], "data_in", [[INPUT_ARG]] : i32, !smt.bv<8>
// CHECK: dbg.trace [[STEP]], "state_q", [[REG_ARG]] : i32, !smt.bv<8>
// CHECK: [[CIRCUIT_RESULT:%.+]] = func.call @bmc_circuit{{(_[0-9]+)?}}([[CLK_ARG]], [[INPUT_ARG]], [[REG_ARG]]) : (!smt.bv<1>, !smt.bv<8>, !smt.bv<8>) -> !smt.bv<8>
// CHECK-NOT: smt.declare_fun "input_1"
// CHECK-NOT: smt.declare_fun "reg_0"
Expand Down
3 changes: 2 additions & 1 deletion test/Dialect/Debug/basic.mlir
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Expand Up @@ -5,9 +5,11 @@ func.func @Foo(%arg0: i32, %arg1: index, %arg2: f64) {
// CHECK-NEXT: dbg.variable "foo", %arg0 : i32
// CHECK-NEXT: dbg.variable "bar", %arg1 : index
// CHECK-NEXT: dbg.variable "baz", %arg2 : f64
// CHECK-NEXT: dbg.trace %arg0, "tracefoo", %arg2 : i32, f64
dbg.variable "foo", %arg0 : i32
dbg.variable "bar", %arg1 : index
dbg.variable "baz", %arg2 : f64
dbg.trace %arg0, "tracefoo", %arg2 : i32, f64

// CHECK-NEXT: [[TMP:%.+]] = dbg.struct {"foo": %arg0, "bar": %arg1, "baz": %arg2} : i32, index, f64
// CHECK-NEXT: dbg.variable "megafoo", [[TMP]] : !dbg.struct
Expand All @@ -28,4 +30,3 @@ func.func @Foo(%arg0: i32, %arg1: index, %arg2: f64) {

return
}

@TaoBi22 TaoBi22 Jul 1, 2026

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nit: unrelated change