3.6.2.4.2 LATENCY_REDUCTION

The LATENCY_REDUCTION settings control the SmartHLS's expression balancing optimization, of which the objective is to reduce the circuit latency. Below are the related settings:

Parameter NameDefault ValueDescription
LATENCY_REDUCTION1The main switch that enables or disables expression balancing. Setting to 0 disables all expression balancing optimizations.
LATENCY_REDUCTION_ALLOW_FP_REORDERING0By default, expression balancing does not re-order floating-point operations to prevent loss of precisions.

Setting to 1 allows to re-order floating-point operations if the circuit latency can be reduced.

LATENCY_REDUCTION_REDUCE_FP_CONVERSIONS 0

Setting to 1 will allow SmartHLS™ to cancel out back-and-forth conversion between floating-point and integer, with potential variations in numerical values.

For example, the following conversions can be cancelled when this setting is 1.

int a = (int)(float)(3); // a == 3.

float b = (float)(int)(1.2); // b == 1.2 instead of 1.

LATENCY_REDUCTION_BALANCE_MULTI_USE_NODE0

By default expression balancing does not optimize the intermediate operations that have multiple uses, to avoid potential increase of resource usage.

Setting to 1 allows to re-order intermediate operations that have multiple uses and more latency reduction could be achieved.

Category
HLS Constraints
Value Type
Integer
Valid Values
0, 1
Default Value
As listed in the table above.
Location Where Default is Specified
examples/legup.tcl
Dependencies
None
Applicable Flows
All devices and flows
Test Status
Actively in-use
Examples
set_parameter LATENCY_REDUCTION 1
set_parameter LATENCY_REDUCTION_ALLOW_FP_REORDERING 0
set_parameter LATENCY_REDUCTION_REDUCE_FP_CONVERSIONS 0
set_parameter LATENCY_REDUCTION_BALANCE_MULTI_USE_NODE 0