updated FlowVariables.md

Signed-off-by: Cho Moon <[email protected]>

Author: precisionmoon

docs/user/FlowVariables.md

@@ -219,6 +219,7 @@ configuration file.
 | <a name="SKIP_PIN_SWAP"></a>SKIP_PIN_SWAP| Do not use pin swapping as a transform to fix timing violations (default: use pin swapping).| |
 | <a name="SKIP_REPORT_METRICS"></a>SKIP_REPORT_METRICS| If set to 1, then metrics, report_metrics does nothing. Useful to speed up builds.| |
 | <a name="SLEW_MARGIN"></a>SLEW_MARGIN| Specifies a slew margin when fixing max slew violations. This option allows you to overfix.| |
+| <a name="SWAP_ARITH_OPERATORS"></a>SWAP_ARITH_OPERATORS| Improve timing QoR by swapping ALU and MULT arithmetic operators.| |
 | <a name="SYNTH_ARGS"></a>SYNTH_ARGS| Optional synthesis variables for yosys.| |
 | <a name="SYNTH_BLACKBOXES"></a>SYNTH_BLACKBOXES| List of cells treated as a black box by Yosys. With Bazel, this can be used to run synthesis in parallel for the large modules of the design.| |
 | <a name="SYNTH_GUT"></a>SYNTH_GUT| Load design and remove all internal logic before doing synthesis. This is useful when creating a mock .lef abstract that has a smaller area than the amount of logic would allow. bazel-orfs uses this to mock SRAMs, for instance.| |