[Synth] Add SOP balancing pass for delay optimization#9511
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This commit introduces a new pass, SOPBalancing, in the Synth dialect to perform delay optimization by restructuring And-Inverter Graphs (AIGs) through sum-of-products (SOP) balancing. The implementation is based on the algorithm described in "Delay Optimization Using SOP Balancing" by Mishchenko et al. (ICCAD 2011), which derives ISOP representations for cuts, balances SOP expressions to minimize critical path delay, and selects optimal cuts based on delay-area trade-offs. Specifically, the changes add the getInputArrivalTimes method to the Cut class for computing input delays, define the SOPBalancing pass with configurable options such as the maximum cut input size, integrate the pass into the synthesis optimization pipeline with a disable option, add the command-line flag --enable-sop-balancing to the circt-synth tool as an opt-in pass. The pass uses cut-based rewriting and is disabled by default for conservative adoption.
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fabianschuiki
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LGTM! Really cool that circt-synth is growing some delay optimizations 🥳
| // | ||
| // First, determine which variables are actually used in the SOP by | ||
| // collecting a bitmask from all cubes. | ||
| uint64_t mask = 0; |
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Is the cube mask guaranteed to fit within 64 bits?
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Realistically yes because truth tables grow exponentially (2^n entries for n variables), so practical limits are much lower than 64. I'll add a check in CutRewriter in a follow-up.
| // COMMON-NEXT: Found 168 paths | ||
| // COMMON-NEXT: Found 32 unique end points | ||
| // AIG-NEXT: Maximum path delay: 32 | ||
| // AIG-NEXT: Maximum path delay: 27 |
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This commit introduces a new pass, SOPBalancing, in the Synth dialect to perform delay optimization by restructuring And-Inverter Graphs (AIGs) through sum-of-products (SOP) balancing. The implementation is based on the algorithm described in "Delay Optimization Using SOP Balancing" by Mishchenko et al. (ICCAD 2011), which derives ISOP representations for cuts, balances SOP expressions to minimize critical path delay, and selects optimal cuts based on delay-area trade-offs. Specifically, the changes add the getInputArrivalTimes method to the Cut class for computing input delays, define the SOPBalancing pass with configurable options such as the maximum cut input size, integrate the pass into the synthesis optimization pipeline with a disable option, add the command-line flag --enable-sop-balancing to the circt-synth tool as an opt-in pass. The pass uses cut-based rewriting and is disabled by default for conservative adoption.
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This commit introduces a new pass, SOPBalancing, in the Synth dialect to perform delay optimization by restructuring And-Inverter Graphs (AIGs) through sum-of-products (SOP) balancing. The implementation is based on the algorithm described in "Delay Optimization Using SOP Balancing" by Mishchenko et al. (ICCAD 2011), which derives ISOP representations for cuts, balances SOP expressions to minimize critical path delay, and selects optimal cuts based on delay-area trade-offs.
The pass uses cut-based rewriting and is disabled by default for now. There are several improvements necessary for CutRewriter framework to make it practical.