Processor and method for speculatively executing instructions from multiple instruction streams indicated by a branch instruction

In a microprocessor, a method for processing instructions in a program including a branch instruction having a condition to be resolved, a first code section to be processed if the condition is resolved to be met, and a second code section to be processed if the condition is resolved to be not met, the method comprising the steps of:

• fetching the branch instruction;
• predicting whether the condition will be resolved to be met;
• determining whether the resolution of the condition is unlikely to be predicted accurately;
• and
• forking the program flow to speculatively process instructions from both the first and second code sections if the resolution of the condition is determined to be unlikely to be predicted accurately.

The method as set forth in claim 18 further including the following steps:

• resolving the condition;
• aborting processing of the second code section if the condition is resolved to be met;
• aborting processing of the first code section if the condition is resolved to be not met;
• invalidating the instruction pointer associated with the aborted code section;
• completing processing of instructions in non-aborted code sections;
• and
• committing results of instructions in non-aborted code sections to architectural state.

A computer system comprising:

• a memory that stores instructions in a program flow, the program flow including a branch instruction having a condition to be resolved, a first code section to be processed if the condition is resolved to be met and a second code section to be processed if the condition is resolved to be not met;
• a bus coupled to the memory that communicates information;
• and
• a microprocessor including:
• a fetch unit that fetches instructions in the program flow from the memory,
• branch prediction logic coupled to the fetch unit that predicts the resolution of the condition and that determines whether the resolution of the condition is unlikely to be predicted accurately, and
• stream management logic responsive to the branch prediction logic that directs speculative processing of instructions from both the first and second code sections prior to resolution of the condition if the resolution of the condition is determined to be unlikely to be predicted accurately.