Abstract: A processor architecture for providing many-to-one mappings between logical registers and physical registers, so that more than one logical register may map to the same physical register. Each physical register has an associated counter to indicate whether the physical register is free. A counter is incremented each time a mapping is made to its associated physical register, and is decremented when that mapping is no longer needed. If a logical register named in a decoded instruction is predicted to have the same value as a value stored in a physical register, then the logical register is mapped to the physical register.

Abstract: A method of executing instructions in an instruction window including the following actions. Examining the first and second instructions to determine the sources and destinations of the first and second instructions. Setting a written on bit of the first instruction to written on if the destinations of the first and second instructions are the same. Setting a used bit of the first instruction to used if the source of the second instruction is the destination of the first instruction. Determining a priority of the first instruction from the written on and used bits.

Abstract: A method and apparatus for improving branch prediction, the method including determining a target of a branch instruction; storing the target of the branch instruction before the branch instruction is fully executed; and re-encountering the branch instruction and predicting a target for the branch instruction by accessing the stored target for the branch instruction.

Abstract: A method for renaming a source for use with a processor, the method including providing an instruction, building instruction dependency information based on the instruction, caching the instruction based on the instruction dependency information to provide a cached instruction, renaming a register based on the cached instruction to provide a renamed register, and multiplexing the instruction dependency information and the renamed register to rename the source.

Abstract: Apparatus and methods to filter memory record updates. A microprocessor can include a memory record update filter. The memory record update filter can include a table memory populated by a plurality of data entries. Each data entry can include a data tag field to store a data tag, a data field to store a data value, and a filter field to store a filter value. A first comparator can be in communication with the data tag field of the table memory and a data accessing information input to perform a data tag comparison. A second comparator can be in communication with the filter field of the table memory and a data value input. A control circuit can be in communication with the table memory, the first comparator, and the second comparator.

Abstract: An electronic device including a predictor that has a collision history table (CHT) is presented. An extended load buffer is connected to the predictor. Also included is a marking unit, a comparing unit and a recovery unit connected to the extended load buffer. Unexecuted load instructions are advanced over store instructions. Also presented is a method for fetching an instruction and determining if an instruction is a store or a load. If the instruction is a store, then the method performs a silent store prediction. If the instruction is a load, a predicted silent store instruction is bypassed and the load instruction is executed.

Abstract: A microprocessor having a correlated address predictor, and methods of performing correlated address prediction. A first table memory can be populated by a plurality of buffer entries. Each buffer entry can include a first buffer field to store a first tag based on an instruction pointer and a second buffer field to store an address history. A second table memory can be populated by a plurality of link entries. Each link entry can include a first link field to store a link tag based on an address history and a second link field to store a predicted address. A first comparator can be in communication with the first table memory and an instruction pointer input. A second comparator can be in communication with the first table memory and the second table memory. An output in communication with the second table memory.

Abstract: A cache management logistics controls a transfer of a trace. A first cache couples to the cache management logistics to evict the trace based on a replacement mechanism. A second cache couples to the cache management logistics to receive the trace based on a number of accesses to the trace.

Abstract: A multi-mode predictor for a processor having a plurality of prediction modes is disclosed. The prediction modes are used to predict non-binary values. The predictor is a multi-mode predictor comprising a per-IP (“PIP”) table and a next value table. The PIP table includes a plurality of PIP information fields and the next value table includes a plurality of fields. The multi-mode predictor also includes a plurality of prediction modes. The processor includes a set of instructions that index the PIP table to provide a valid signal. The processor also includes a set of predicted values for the set of instructions. The set of predicted values is stored in the PIP table and the next value table. According to the valid signal a hit/miss condition in the next value table, a predicted value is selected from the PIP table or the next value table.

Abstract: A branch predicting apparatus is disclosed that reduces branch mispredictions in a processor. The branch prediction apparatus includes a base misprediction history register. The branch prediction apparatus includes a meta predictor that receives an index value and a branch prediction to generate a misprediction value in accordance with the base misprediction history register. The branch prediction apparatus also includes a logic gate that receives the branch prediction and the misprediction value to generate a final prediction. The final prediction may be used to predict whether a branch is taken or not taken.

Abstract: A processor having a register renaming structure and method is disclosed to recover a free list. The processor includes a physical register file including physical registers. The processor also includes a decoder to decode an instruction to indicate a destination logical register. The processor also includes a register allocation table to map the destination logical register to an allocated physical register. The processor also includes an active list that includes an old field and a new field. The old field includes at least one evicted physical register from the register alias table. The new field includes the allocated physical register. The processor also includes the free list of unallocated physical registers reclaimed from the active list.

Abstract: A system and method for producing a fused instruction is described. In one embodiment, a first instruction and a second instruction that are both simple instructions (e.g., perform only one operation) and are dependent are fused together to create the fused instruction. The fused instruction has an opcode that represents the operation performed by the first instruction and the operation performed by the second instruction. The fused instruction has three source operands and one destination operand. Two of the three source operands are the two source operands of the first instruction, and the third source operand is the source operand of the second instruction that is not the destination operand of the first instruction. The destination operand of the fused instruction is the destination operand of the second instruction. An execution unit that can execute a fused instruction in one clock cycle is also disclosed.

Abstract: A system and corresponding method use a PAUSE instruction as a low power hint in a single threaded or multithreaded environment using “processor slow mode.” One embodiment actually lowers the frequency of the processor clock. Another embodiment virtually lowers the frequency of the processor clock by gating M clock cycles out of every N clock cycles. When all threads have issued a PAUSE instruction, the processor enters slow mode and remains there for a while. After this while, the processor returns to normal mode. Alternatively, an event, such as an interrupt or an exception, can cause the processor to return to normal mode from slow mode.

Abstract: Apparatus and methods to filter memory record updates. A microprocessor can include a memory record update filter. The memory record update filter can include a table memory populated by a plurality of data entries. Each data entry can include a data tag field to store a data tag, a data field to store a data value, and a filter field to store a filter value. A first comparator can be in communication with the data tag field of the table memory and a data accessing information input to perform a data tag comparison. A second comparator can be in communication with the filter field of the table memory and a data value input. A control circuit can be in communication with the table memory, the first comparator, and the second comparator.

Abstract: A microprocessor includes an execution engine, a prediction table cache, and a prefetch controller. The execution engine is adapted to issue a memory request. The memory request includes an identifier corresponding to a row location in an external main memory. The prediction table cache is adapted to store a plurality of entries defining an access history of previously encountered memory requests. The prediction table cache is indexed by the identifier. The prefetch controller is adapted to receive the memory request and generate at least one prefetch candidate based on the memory request and the access history. A method for prefetching data in a microprocessor includes receiving a memory request. The memory request includes an identifier corresponding to a row location in an external main memory. The memory request is compared to an access history of previously encountered memory requests. The access history is indexed by the identifier.

Abstract: The invention in several embodiments includes an apparatus and a method for predicting whether store instructions can be safely executed out-of-order. The apparatus, includes at least one execution unit, a reorder buffer adapted to holding a plurality of instructions from an instruction sequence for execution by the execution units, and a memory storage device adapted to holding a collision history table. The collision history table has entries for load instructions of the instruction sequence Each of the entries is adapted to predicting when the associated load instruction is colliding.

Abstract: An advanced register renamer comprises an associative memory having a plurality of entries, each entry storing a representation of a single operation as an expression paired with a corresponding name. The expression and the name are respectively stored in first and second fields of an entry in the memory. Both fields are available for subsequent assembly level operations to use as pattern matches. A means for converting a subsequent operation in the stream to a new operation searches for a match between an expression of the subsequent operation and the first field of a matching entry. Upon finding a match with the expression field in the table, the subsequent operation is renamed to a new operation by replacing the expression with the corresponding name field of the matching entry taken from the associative memory.

Abstract: A method and apparatus for executing instructions in a pipelined microprocessor. The method includes re-ordering the set of instructions prior to loading the instructions into an instruction cache. In one embodiment, a re-ordering unit receives the set of instructions as a trace segment made of a set of basic blocks of instructions in a logical order of execution. After being re-ordered, the instructions are presented to the reordered instruction cache in bundles. When an instruction is unavailable, possibly due to an unresolved data dependency, no operation codes (nops) are inserted into the bundle in place of an in place of an instruction, creating fixed length bundles. In a second embodiment, nops are not used. Variable length bundles are produced by using an additional bit(s) per instruction to mark the end of the bundles.

Abstract: A method of processor architecture modification includes the step of defining an instruction set architecture for a current generation processor. Reserved within this definition are a set of instructions which perform no-operations (NOPs), have no attached semantics, and do not change any architectural state of the processor. Software code, compatible with the instruction set architecture, is then written for running on the processor. In a next-generation processor, new functionality is added by defining a semantic for one of the NOPs so that programs which utilize the new instruction run on both the current-generation and the next-generation processors.