A method, system, and computer usable program product for energy-efficient soft error failure detection and masking are provided in the illustrative embodiments. A soft error is injected to occur during execution of a set of instructions. If an output of the execution of the set of instructions is incorrect, a record is made of the instruction that was affected by the injected soft error and led to the incorrect result. This identified instruction is designated as vulnerable to the soft error. Several soft errors are injected with different input data sets over several executions of the same set of instructions, and a probability of each instruction in the instruction set is computed, the probability of an instruction accounting for the vulnerability of the execution of the instruction sets to errors that affect the instruction. A report including several probabilities of instruction vulnerabilities is produced.