3.6.1.16 Strict-X Option

The -mstrict-X option ensures that the X register (r26-r27) is only used in indirect, post-increment or pre-decrement addressing. This restricts the register’s usage, which could be beneficial in terms of code size.

The -mno-strict-X form of this option allows the compiler to use the X register for indexed addressing (X+const, X-const). This is the default action if no option is specified.