Abstract: A system and method for efficiently reducing the latency and power of memory access operations. A processor includes a stack pointer (SP) load-store dependence (LSD) predictor which predicts whether a memory dependence exists on a store instruction. The processor also includes a register file (RF) LSD predictor which predicts whether a memory dependence exists on a store instruction or a load instruction by a subsequent load instruction in program order. Each of the SP-LSD predictor and the RF-LSD predictor predicts and performs register renaming in a pipeline stage earlier than a renaming pipeline stage. The RF-LSD predictor also determines whether any intervening instructions between a producer memory instruction and a consumer memory instruction modify a predicted dependence.

Abstract: In some embodiments, a branch prediction unit includes a plurality of branch prediction circuits and selection logic. At least two of the branch prediction circuits are configured, based on an address of a branch instruction and different sets of history information, to provide a corresponding branch prediction for the branch instruction. At least one storage element of the at least two branch prediction circuits is set associative. The selection logic is configured to select a particular branch prediction output by one of the branch prediction circuits as a current branch prediction output of the branch prediction unit. In some instances, the branch prediction unit may be less likely to replace branch prediction information, as compared to a different branch prediction unit that does not include a set associative storage element. In some embodiments, this arrangement may lead to increased performance of the branch prediction unit.

Abstract: A system and method for efficiently protecting branch prediction information. In various embodiments, a computing system includes at least one processor with a branch predictor storing branch target addresses and security tags in a table. The security tag includes one or more components of machine context. When the branch predictor receives a portion of a first program counter of a first branch instruction, and hits on a first table entry during an access, the branch predictor reads out a first security tag. The branch predictor compares one or more components of machine context of the first security tag to one or more components of machine context of the first branch instruction. When there is at least one mismatch, the branch prediction information of the first table entry is not used. Additionally, there is no updating of any branch prediction training information of the first table entry.

Abstract: Systems, apparatuses, and methods for efficiently scheduling processor instructions for execution. The reservation station in a processor stores instructions in each of a primary buffer and a secondary buffer. Control logic selects a first number of instructions with ready source operands in the primary buffer and a second number of instructions with ready source operands in the secondary buffer. If a third number of instructions to issue from the reservation station is greater than the first number of instructions, then the reservation station issues one or more instructions of the second number of instructions from the secondary buffer to the one or more execution units. Control logic selects a fourth number of instructions in the secondary buffer to transfer to the primary buffer, and cancels the transfer of a given instruction in response to determining the given instruction has issued to the one or more execution units.

Abstract: A processor includes a mechanism for disabling a memory array of a branch prediction unit. The processor may include a next fetch prediction unit that may include a number of entries. Each entry may correspond to a next instruction fetch group and may store an indication of whether or not the corresponding the next fetch group includes a conditional branch instruction. In response to an indication that the next fetch group does not include a conditional branch instruction, the fetch prediction unit may be configured to disable, in a next instruction execution cycle, the memory array of the branch prediction unit.

Abstract: In an embodiment, an apparatus includes a plurality of memories configured to store respective data in a plurality of branch prediction entries. Each branch prediction entry corresponds to at least one of a plurality of branch instructions. The apparatus also includes a control circuit configured to store first data associated with a first branch instruction into a corresponding branch prediction entry in at least one memory of the plurality of memories. The control circuit is further configured to select a first memory of the plurality of memories, to disconnect the first memory from a power supply in response to a detection of a first power mode signal, and to cease storing data in the plurality of memories in response to the detection of the first power mode signal.

Abstract: A processor includes a mechanism for disabling a memory array of a branch prediction unit. The processor may include a next fetch prediction unit that may include a number of entries. Each entry may correspond to a next instruction fetch group and may store an indication of whether or not the corresponding the next fetch group includes a conditional branch instruction. In response to an indication that the next fetch group does not include a conditional branch instruction, the fetch prediction unit may be configured to disable, in a next instruction execution cycle, the memory array of the branch prediction unit.

Abstract: In an embodiment, an apparatus includes a plurality of memories configured to store respective data in a plurality of branch prediction entries. Each branch prediction entry corresponds to at least one of a plurality of branch instructions. The apparatus also includes a control circuit configured to store first data associated with a first branch instruction into a corresponding branch prediction entry in at least one memory of the plurality of memories. The control circuit is further configured to select a first memory of the plurality of memories, to disconnect the first memory from a power supply in response to a detection of a first power mode signal, and to cease storing data in the plurality of memories in response to the detection of the first power mode signal.

Abstract: A method and system for storing branch information is disclosed. First data may be stored in a first entry of a first table in response to a determination that a fetched instruction is a branch instruction. Second data that is dependent upon at least one previously taken branch may be stored in a second entry in a second table in response to a determination that a branch associated with the instruction is predicted to be taken. The first data may be updated to include an index to the second data in response to the determination that the branch is predicted to be taken.

Abstract: Techniques are disclosed relating to capturing information related to instructions executing on in a processor. In one embodiment, an integrated circuit is disclosed that includes an execution pipeline configured to execute a sequence of instructions. The integrated circuit includes monitoring circuitry configured to monitor the execution pipeline for occurrences of an event associated with the sequence of instructions, and in response to detecting a particular number of occurrences of the event, capture a value of a program counter corresponding to an instruction of the sequence of instructions that is associated with an occurrence of the event. The monitoring circuitry stores the captured value of the program counter in a distinct capture register and signals an interrupt indicating that the captured value of the program counter is retrievable from the capture register. In some embodiments, a debugging application may retrieve the value and present it to a developer attempting perform code profiling.

Abstract: A system and method for efficiently indicating branch target addresses. A semiconductor chip predecodes instructions of a computer program prior to installing the instructions in an instruction cache. In response to determining a particular instruction is a control flow instruction with a displacement relative to a program counter address (PC), the chip replaces a portion of the PC relative displacement in the particular instruction with a subset of a target address. The subset of the target address is an untranslated physical subset of the full target address. When the recoded particular instruction is fetched and decoded, the remaining portion of the PC relative displacement is added to a virtual portion of the PC used to fetch the particular instruction. The result is concatenated with the portion of the target address embedded in the fetched particular instruction to form a full target address.

Abstract: Methods, apparatuses, and processors for packing multiple iterations of a loop in a loop buffer. A loop candidate that meets the criteria for buffering is detected in the instruction stream being executed by a processor. When the loop is being written to the loop buffer and the end of the loop is detected, another iteration of the loop is written to the loop buffer if the loop buffer is not yet halfway full. In this way, short loops are written to the loop buffer multiple times to maximize the instruction operations per cycle throughput out of the loop buffer when the processor is in loop buffer mode.

Abstract: A processor and method for fusing together an arithmetic instruction and a branch instruction. The processor includes an instruction fetch unit configured to fetch instructions. The processor may also include an instruction decode unit that may be configured to decode the fetched instructions into micro-operations for execution by an execution unit. The decode unit may be configured to detect an occurrence of an arithmetic instruction followed by a branch instruction in program order, wherein the branch instruction, upon execution, changes a program flow of control dependent upon a result of execution of the arithmetic instruction. In addition, the processor may further be configured to fuse together the arithmetic instruction and the branch instruction such that a single micro-operation is formed. The single micro-operation includes execution information based upon both the arithmetic instruction and the branch instruction.

Abstract: In an embodiment, a processor includes a register file having multiple widths corresponding to different operands sizes of a given data type implemented by the processor. For example, the integer register file may have 32 bit and 64 bit widths for 32 and 64 bit operand sizes. The register file may have a section of registers for each operand size, and the map unit may allocate registers from the appropriate section for each instruction operation based on the operand size of that instruction operation. The register file may consume less integrated circuit area than another register file having the same number of registers, all of which are implemented at the largest operand size. In some embodiments, only the register file and the map unit (specifically the free list management logic in the map unit) are changed to implement the multiple-width register file.

Abstract: Various techniques for processing and pre-decoding branches within an IT instruction block. Instructions are fetched and cached in an instruction cache, and pre-decode bits are generated to indicate the presence of an IT instruction and the likely boundaries of the IT instruction block. If an unconditional branch is detected within the likely boundaries of an IT instruction block, the unconditional branch is treated as if it were a conditional branch. The unconditional branch is sent to the branch direction predictor and the predictor generates a branch direction prediction for the unconditional branch.

Abstract: A system and method for reducing the latency of data move operations. A register rename unit within a processor determines whether a decoded move instruction is eligible for a zero cycle move operation. If so, control logic assigns a physical register identifier associated with a source operand of the move instruction to the destination operand of the move instruction. Additionally, the register rename unit marks the given move instruction to prevent it from proceeding in the processor pipeline. Further maintenance of the particular physical register identifier may be done by the register rename unit during commit of the given move instruction.

Abstract: Methods, apparatuses, and processors for tracking loop candidates in an instruction stream. A load buffer control unit detects a backwards taken branch and starts tracking the loop candidate. The control unit tracks taken branches of the loop candidate, and keeps track of the distance to each taken branch from the start of the loop. If the distance to each taken branch stays the same over multiple iterations of the loop, then the loop is stored in a loop buffer. The loop is then dispatched from the loop buffer, and the front-end of the processor is powered down until the loop terminates.

Abstract: Systems, apparatuses, methods, and computer-readable mediums for preventing return oriented programming (ROP) attacks. A compiler may insert landing pads adjacent to valid return targets in an instruction sequence. When a return instruction is executed, the processor may treat the return as suspicious if the target of the return instruction does not have an adjacent landing pad. Additionally, each landing pad may be encoded with a color, and a colored launch pad may be inserted into the instruction stream next to each return instruction. When a return instruction is executed, the processor may determine if the target of the return has a landing pad with the same color as the launch pad of the return instruction. Return-target pairs with color mismatches may be treated as suspicious and the offending process may be killed.

Abstract: A processor includes a mechanism that checks for and flushes only speculative loads and any respective dependent instructions that are younger than an executed wait for event (WEV) instruction, and which also match an address of a store instruction that has been determined to have been executed by a different processor prior to execution of the paired SEV instruction by the different processor. The mechanism may allow speculative loads that do not match the address of any store instruction that has been determined to have been executed by a different processor prior to execution of the paired SEV instruction by the different processor.

Abstract: Systems, processors, and methods for determining when to enter loop buffer mode early for loops in an instruction stream. A processor waits until a branch history register has saturated before entering loop buffer mode for a loop if the processor has not yet determined the loop has an unpredictable exit. However, if the loop has an unpredictable exit, then the loop is allowed to enter loop buffer mode early. While in loop buffer mode, the loop is dispatched from a loop buffer, and the front-end of the processor is powered down until the loop terminates.