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[mlir][cf] Preserve branch weights during cf.cond_br canonicalization. #144822

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Merged
merged 1 commit into from
Jun 19, 2025
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[mlir][cf] Preserve branch weights during cf.cond_br canonicalization. #144822

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20 changes: 14 additions & 6 deletions mlir/include/mlir/Dialect/ControlFlow/IR/ControlFlowOps.td
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Original file line number Diff line number Diff line change
Expand Up @@ -153,17 +153,25 @@ def CondBranchOp
let builders = [OpBuilder<(ins "Value":$condition, "Block *":$trueDest,
"ValueRange":$trueOperands,
"Block *":$falseDest,
"ValueRange":$falseOperands),
"ValueRange":$falseOperands,
CArg<"ArrayRef<int32_t>", "{}">:$branchWeights),
[{
build($_builder, $_state, condition, trueOperands, falseOperands, /*branch_weights=*/{}, trueDest,
falseDest);
DenseI32ArrayAttr weights;
if (!branchWeights.empty())
weights = $_builder.getDenseI32ArrayAttr(branchWeights);
build($_builder, $_state, condition, trueOperands, falseOperands,
weights, trueDest, falseDest);
}]>,
OpBuilder<(ins "Value":$condition, "Block *":$trueDest,
"Block *":$falseDest,
CArg<"ValueRange", "{}">:$falseOperands),
CArg<"ValueRange", "{}">:$falseOperands,
CArg<"ArrayRef<int32_t>", "{}">:$branchWeights),
[{
build($_builder, $_state, condition, trueDest, ValueRange(), falseDest,
falseOperands);
DenseI32ArrayAttr weights;
if (!branchWeights.empty())
weights = $_builder.getDenseI32ArrayAttr(branchWeights);
build($_builder, $_state, condition, ValueRange(), falseOperands,
weights, trueDest, falseDest);
}]>];

let extraClassDeclaration = [{
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6 changes: 3 additions & 3 deletions mlir/lib/Dialect/ControlFlow/IR/ControlFlowOps.cpp
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Expand Up @@ -265,9 +265,9 @@ struct SimplifyPassThroughCondBranch : public OpRewritePattern<CondBranchOp> {
return failure();

// Create a new branch with the collapsed successors.
rewriter.replaceOpWithNewOp<CondBranchOp>(condbr, condbr.getCondition(),
trueDest, trueDestOperands,
falseDest, falseDestOperands);
rewriter.replaceOpWithNewOp<CondBranchOp>(
condbr, condbr.getCondition(), trueDest, trueDestOperands, falseDest,
falseDestOperands, condbr.getWeights());
return success();
}
};
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25 changes: 25 additions & 0 deletions mlir/test/Dialect/ControlFlow/canonicalize.mlir
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Expand Up @@ -102,6 +102,31 @@ func.func @cond_br_and_br_folding(%a : i32) {

/// Test that pass-through successors of CondBranchOp get folded.

// Test that the weights are preserved:
// CHECK-LABEL: func.func @cond_br_passthrough_weights(
// CHECK-SAME: %[[ARG0:.*]]: i32, %[[ARG1:.*]]: i32, %[[ARG2:.*]]: i1) -> i32 {
func.func @cond_br_passthrough_weights(%arg0 : i32, %arg1 : i32, %cond : i1) -> i32 {
// CHECK: cf.cond_br %[[ARG2]] weights([30, 70]), ^bb1, ^bb2
// CHECK: ^bb1:
// CHECK: return %[[ARG0]] : i32
// CHECK: ^bb2:
// CHECK: return %[[ARG1]] : i32
// CHECK: }
cf.cond_br %cond weights([30,70]), ^bb1, ^bb3

^bb1:
cf.br ^bb2

^bb3:
cf.br ^bb4

^bb2:
return %arg0 : i32

^bb4:
return %arg1 : i32
}

// CHECK-LABEL: func @cond_br_passthrough(
// CHECK-SAME: %[[ARG0:.*]]: i32, %[[ARG1:.*]]: i32, %[[ARG2:.*]]: i32, %[[COND:.*]]: i1
func.func @cond_br_passthrough(%arg0 : i32, %arg1 : i32, %arg2 : i32, %cond : i1) -> (i32, i32) {
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