Which gcc pass optimizes the value of variables away -

when compiling gcc optimization. values of variables optimized out. know gcc pass optimizes variables value out, can disable such pass keep variables unoptimized? thanks.

your question quite vague, should take @ flags such -fssa-backprop. according gcc documentation:

propagate information uses of value definition chain in order simplify definitions. example, pass strips sign operations if sign of value never matters.

this optimisation turned on @ level -o1 (and higher levels of optimisation well).