Checkpointing speculative register mappings

An apparatus comprising:

• means for performing data processing in response to micro-operations;
• means for mapping logical registers specified by the micro-operations to physical registers provided in hardware;
• means for capturing register mapping checkpoints, each register mapping checkpoint indicative of speculative register mappings between logical registers and physical registers at a given point of speculative execution;
• and
• means for maintaining tracking information for a plurality of groups of logical registers, each group comprising one or more logical registers, the tracking information for a given group indicating whether the given group is a changed group comprising at least one logical register for which a corresponding speculative register mapping has changed since a last register mapping checkpoint was captured, or an unchanged group for which none of the logical registers in that group have had their speculative register mappings changed since the last register mapping checkpoint was captured;
• in which:
• when capturing a new register mapping checkpoint, the means for capturing is configured to exclude from the new register mapping checkpoint the speculative register mappings for logical registers in an unchanged group of logical registers.

A data processing method comprising:

• performing data processing in response to micro-operations;
• mapping logical registers specified by the micro-operations to physical registers provided in hardware;
• capturing register mapping checkpoints, each register mapping checkpoint indicative of speculative register mappings between logical registers and physical registers at a given point of speculative execution;
• and
• maintaining tracking information for a plurality of groups of logical registers, each group comprising one or more logical registers, the tracking information for a given group indicating whether the given group is a changed group comprising at least one logical register for which a corresponding speculative register mapping has changed since a last register mapping checkpoint was captured, or an unchanged group for which none of the logical registers in that group have had their speculative register mappings changed since the last register mapping checkpoint was captured;
• in which:
• when a new register mapping checkpoint is captured, speculative register mappings for logical registers in an unchanged group of logical registers are excluded from the new register mapping checkpoint.