https://www.synopsys.com/implementation-and-signoff/test-automation/testmax-xlbist.html
TestMAX XLBIST: X-Tolerant Logic Built-in Self-Test (BIST) | Synopsys
TestMAX XLBIST provides in-system self-test solutions for critical applications, eliminating unknown logic values (Xs) and meeting ISO 26262 requirements.
logic built in self testxtolerant