Responding to branch misprediction for predicated-loop-terminating branch instruction

A method comprising:

• performing branch prediction to predict outcomes of branch instructions, and based on the branch prediction, controlling fetching of instructions to be decoded for processing by processing circuitry;
• in response to the decoded instructions, performing data processing using the processing circuitry;
• detecting branch misprediction for a predicated-loop-terminating branch instruction for controlling, based on whether a loop termination condition is satisfied, whether the processing circuitry should process a further iteration of a predicated loop body or process a following instruction to be processed after a final iteration of the predicated loop body, for which, if an unnecessary iteration of the predicated loop body is processed following the loop termination condition being mispredicted as unsatisfied for an iteration of the predicated-loop-terminating branch instruction when the loop termination condition should have been predicted satisfied, processing of the unnecessary iteration of the predicated loop body is predicated to suppress an effect of the unnecessary iteration of the predicated loop body;
• and
• in response to detecting a mispredicted-non-termination branch misprediction for a given iteration of the predicated-loop-terminating branch instruction for which the loop termination condition is mispredicted as unsatisfied when the loop termination condition should have been predicted satisfied:
• determining whether a flush suppressing condition is satisfied;
• and
• in response to determining that the flush suppressing condition is satisfied, suppressing flushing of one or more unnecessary iterations of the predicated loop body as a response to the mispredicted-non-termination branch misprediction, to allow the processing circuitry to continue to process the one or more unnecessary iterations despite the mispredicted-non-termination branch misprediction being detected.

A non-transitory computer-readable medium to store computer-readable code for fabrication of an apparatus comprising:

• processing circuitry to perform data processing in response to decoded instructions;
• branch prediction circuitry to perform branch prediction to predict outcomes of branch instructions, and based on the branch prediction, to control fetching of instructions to be decoded for processing by the processing circuitry;
• and
• branch misprediction detection circuitry to detect branch misprediction for a predicated-loop-terminating branch instruction for controlling, based on whether a loop termination condition is satisfied, whether the processing circuitry should process a further iteration of a predicated loop body or process a following instruction to be processed after a final iteration of the predicated loop body, for which, if an unnecessary iteration of the predicated loop body is processed following the loop termination condition being mispredicted as unsatisfied for an iteration of the predicated-loop-terminating branch instruction when the loop termination condition should have been predicted satisfied, processing of the unnecessary iteration of the predicated loop body is predicated to suppress an effect of the unnecessary iteration of the predicated loop body;
• in which:
• in response to detecting a mispredicted-non-termination branch misprediction for a given iteration of the predicated-loop-terminating branch instruction for which the loop termination condition is mispredicted as unsatisfied when the loop termination condition should have been predicted satisfied, the branch misprediction detection circuitry is configured to:
• determine whether a flush suppressing condition is satisfied;
• and
• in response to determining that the flush suppressing condition is satisfied, suppress flushing of one or more unnecessary iterations of the predicated loop body as a response to the mispredicted-non-termination branch misprediction, to allow the processing circuitry to continue to process the one or more unnecessary iterations despite the mispredicted-non-termination branch misprediction being detected.