3.6.2.4.19 STRENGTH_REDUCTION_ADDERS_ALLOWED_PER_MULTIPLIER
(Ask a Question)Strength reduction is an optimization that converts multiply-by-constant into shifts and additions:
Info: StrengthReduction: Replacing multiply by constant (i26 33038) with 3 adders:
- (1 << 1) + (1 << 4) + (1 << 8) + (1 << 15)
The STRENGTH_REDUCTION_ADDERS_ALLOWED_PER_MULTIPLIER constraint allows you to tune the number of adders allowed per multiplier (default is 3). Strength reduction for multiply-by-constants will not be performed if this requires more adders than allowed:
i26 16828 is composed of 4 adders:
- (1 << 2) + (1 << 6) + (1 << 7) + (1 << 8) + (1 << 14)
Skipping conversion otherwise would need too many additions.
In this example, we would need 4 adders which is more than the default of 3, meaning strength reduction will not occur and SmartHLS™ will keep the multiplier.
- Category
- HLS Constraints
- Value Type
- Integer
- Valid Values
- Positive Integer
- Default Value
- 3
- Location Where Default is Specified
examples/legup.tcl- Dependencies
- STRENGTH_REDUCTION must be on
- Applicable Flows
- All devices and flows
- Test Status
- Actively in-use
- Examples
set_parameter STRENGTH_REDUCTION_ADDERS_ALLOWED_PER_MULTIPLIER 3