feat: fused WideDecimalBinaryExpr for Decimal128 add/sub/mul#3619
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andygrove wants to merge 3 commits intoapache:mainfrom
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feat: fused WideDecimalBinaryExpr for Decimal128 add/sub/mul#3619andygrove wants to merge 3 commits intoapache:mainfrom
andygrove wants to merge 3 commits intoapache:mainfrom
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Replace the 4-node expression tree (Cast→BinaryExpr→Cast→Cast) used for Decimal128 arithmetic that may overflow with a single fused expression that performs i256 register arithmetic directly. This reduces per-batch allocation from 4 intermediate arrays (112 bytes/elem) to 1 output array (16 bytes/elem). The new WideDecimalBinaryExpr evaluates children, performs add/sub/mul using i256 intermediates via try_binary, applies scale adjustment with HALF_UP rounding, checks precision bounds, and outputs a single Decimal128 array. Follows the same pattern as decimal_div.
Add benchmark comparing old Cast->BinaryExpr->Cast chain vs fused WideDecimalBinaryExpr for Decimal128 add/sub/mul. Covers four cases: add with same scale, add with different scales, multiply, and subtract.
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@sqlbenchmark run tpch --iterations 3 |
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@sqlbenchmark run tpch --iterations 3 |
Eliminate redundant CheckOverflow when wrapping WideDecimalBinaryExpr (which already handles overflow). Fuse Cast(Decimal128→Decimal128) + CheckOverflow into a single DecimalRescaleCheckOverflow expression that rescales and validates precision in one pass.
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@sqlbenchmark run tpch --iterations 3 |
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Benchmark job |
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Summary
Cast(Decimal256→Decimal128, BinaryExpr(op, Cast(Decimal128→Decimal256, left), Cast(Decimal128→Decimal256, right)))) used for Decimal128 add/sub/mul that may overflow with a single fusedWideDecimalBinaryExprthat performs i256 register arithmetic directlyBenchmark results (8192 element batches)
How it works
WideDecimalBinaryExprevaluates left/right children, performs add/sub/mul usingi256intermediates viaarrow::compute::kernels::arity::try_binary, applies scale adjustment with HALF_UP rounding, checks precision bounds, and outputs a singleDecimal128array. Follows the same pattern asdecimal_divindiv.rs.Overflow handling matches existing behavior:
ArrowError::ComputeErrori128::MAXsentinel +null_if_overflow_precisionTest plan
cargo clippy --all-targets --workspace -- -D warningspassescargo testpassesCometExpressionSuite) pass unchanged