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[LLHD] Allow verif ops in comb canonicalization #9752

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[LLHD] Allow verif ops in comb canonicalization #9752

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6501e3f
[LLHD] Allow verif ops in comb canonicalization
towoe Feb 25, 2026
1511db8
[LLHD] Combine isa checks
towoe Feb 26, 2026
6557634
[LLHD] Add explanation for verif exception
towoe Feb 26, 2026
7df18fa
[LLHD] Add missing dependency
towoe Feb 26, 2026
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37 changes: 29 additions & 8 deletions lib/Dialect/LLHD/IR/LLHDOps.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@

#include "circt/Dialect/Comb/CombOps.h"
#include "circt/Dialect/HW/HWOps.h"
#include "circt/Dialect/Verif/VerifOps.h"
#include "circt/Support/CustomDirectiveImpl.h"
#include "mlir/IR/Attributes.h"
#include "mlir/IR/BuiltinDialect.h"
Expand Down Expand Up @@ -765,14 +766,34 @@ LogicalResult ProcessOp::canonicalize(ProcessOp op, PatternRewriter &rewriter) {
LogicalResult CombinationalOp::canonicalize(CombinationalOp op,
PatternRewriter &rewriter) {
// Inline the combinational region if it consists of a single block and
// contains no side-effecting operations.
if (op.getBody().hasOneBlock() && isMemoryEffectFree(op)) {
auto &block = op.getBody().front();
auto *terminator = block.getTerminator();
rewriter.inlineBlockBefore(&block, op, ValueRange{});
rewriter.replaceOp(op, terminator->getOperands());
rewriter.eraseOp(terminator);
return success();
// contains no side-effecting operations (ignoring verif assert like).
if (op.getBody().hasOneBlock()) {
bool hasUnwantedEffects = false;
op.getBody().walk([&](Operation *inner) {
if (isa<circt::verif::AssertOp>(inner) ||
isa<circt::verif::AssumeOp>(inner) ||
isa<circt::verif::CoverOp>(inner))
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@fabianschuiki fabianschuiki Feb 25, 2026

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You can combine the isas into one 🙂 (probably needs reformatting):

Suggested change
if (isa<circt::verif::AssertOp>(inner) ||
isa<circt::verif::AssumeOp>(inner) ||
isa<circt::verif::CoverOp>(inner))
if (isa<circt::verif::AssertOp, circt::verif::AssumeOp, circt::verif::CoverOp>(inner))

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@towoe towoe Feb 26, 2026

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Thanks, seems like I forgot this from the last time :)

return WalkResult::advance();
if (auto memInterface = dyn_cast<MemoryEffectOpInterface>(inner)) {
if (!memInterface.hasNoEffect()) {
hasUnwantedEffects = true;
return WalkResult::interrupt();
}
} else if (!inner->hasTrait<OpTrait::HasRecursiveMemoryEffects>()) {
hasUnwantedEffects = true;
return WalkResult::interrupt();
}
return WalkResult::advance();
});

if (!hasUnwantedEffects) {
auto &block = op.getBody().front();
auto *terminator = block.getTerminator();
rewriter.inlineBlockBefore(&block, op, ValueRange{});
rewriter.replaceOp(op, terminator->getOperands());
rewriter.eraseOp(terminator);
return success();
}
}
return failure();
}
Expand Down
16 changes: 16 additions & 0 deletions test/Dialect/LLHD/Canonicalization/processes.mlir
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Expand Up @@ -36,6 +36,22 @@ hw.module @InlineCombinational(in %a: i42, in %b: i42, in %c: i8917, out u: i42,
hw.output %0, %1 : i42, i9001
}

// CHECK-LABEL: hw.module @InlineCombinationalVerif(
hw.module @InlineCombinationalVerif(in %a: i1, in %b: i1, in %c: i1, out u: i1, out
v: i3) {
// CHECK-NEXT: [[TMP1:%.+]] = comb.xor %a, %b
// CHECK-NEXT: verif.assert [[TMP1]] label "" : i1
// CHECK-NEXT: [[TMP2:%.+]] = comb.concat %a, %b, %c
// CHECK-NEXT: hw.output [[TMP1]], [[TMP2]]
%0, %1 = llhd.combinational -> i1, i3 {
%2 = comb.xor %a, %b : i1
verif.assert %2 label "" : i1
%3 = comb.concat %a, %b, %c : i1, i1, i1
llhd.yield %2, %3 : i1, i3
}
hw.output %0, %1 : i1, i3
}

// CHECK-LABEL: hw.module @IgnoreMultiBlockHalt
hw.module @IgnoreMultiBlockHalt(in %a : i1, in %b : i1, out v1 : i1, out v2 : i1) {
// CHECK: llhd.halt %a, %a
Expand Down
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