US 2003/0154362 A1 · Method and system for safe data dependency collapsing based on control-flow speculation

Abstract

The present invention is directed to an apparatus and method for data collapsing based on control-flow speculation (conditional branch predictions). Because conditional branch outcomes are resolved based on actual data values, the conditional branch prediction provides potentially valuable insight into data values. Upon encountering a branch if equal instruction and this instruction is predicted as taken or a branch if not equal instruction and this instruction is predicted as not taken, this invention assumes that the two operands used to determine the conditional branch are equal. The data predictions are safe because a data misprediction means a conditional branch misprediction which results in a pipeline flush of the instructions following the conditional branch instruction including the data mispredictions.

Claims28

Dependent claims

An apparatus for collapsing a set of operands, comprising:

a post-decode unit which:
upon decoding one of a set of instructions that modifies its zero flag when executed, records information in a first entry about a set of operands for that particular one of the set of instructions;
upon decoding one of a set of instructions that is at least one of a branch if equal and predicted as taken and a branch if not equal and predicted as not taken, copies the recorded information in the first entry to one of a set of second entries;
and
translates the set of operands for each one of a set of instructions if information is recorded about the set of operands in one of the set of second entries and that recorded information is valid.

2 more elements

A method for collapsing a set of operands, comprising:

upon decoding one of the set of instructions that modifies its zero flag when executed, recording information in a first entry about a set of operands for that particular one of the set of instructions;
upon decoding one of a set of instructions that is at least one of a branch if equal and predicted as taken, and a branch if not equal and predicted as not taken, copying the recorded information in the first entry to one of a set of second entries;
and
collapsing the set of operands for each one of the set of instructions if information is recorded about the set of operands in one of the set of second entries and that recorded information is valid.

1 more element

A method for collapsing a set of operands, comprising:

upon decoding one of a set of instructions that modifies its zero flag when executed, recording information in an entry about a set of operands for that particular one of the set of instructions that modifies its zero flag;
and
remapping an architectural register for one of the set of operands to a physical register for another of the set of operands upon decoding at least one of a branch if equal and predicted as taken and a branch if not equal and predicted as not taken, and the recorded information in the entry is valid.

Dependencies are inferred from the claim text.

Method and system for safe data dependency collapsing based on control-flow speculation

Life of this patent

Method and system for safe data dependency collapsing based on control-flow speculation

Life of this patent

Abstract

Claims28