Abstract: Embodiments disclosed herein include eliminating redundant synchronization barriers from execution pipelines in instruction processing circuits. Related processor systems, methods, and computer-readable media are also disclosed. By tracking the occurrence of synchronization events, unnecessary software synchronization operations may be identified and eliminated, thus improving performance of a central processing unit (CPU). In one embodiment, a method for eliminating redundant synchronization barriers in an instruction stream is provided. The method comprises determining whether a next instruction comprises a synchronization barrier of a type corresponding to a first synchronization event. The method also comprises eliminating the next instruction from the instruction stream, responsive to determining that the next instruction comprises a synchronization barrier of a type corresponding to the first synchronization event.

Abstract: An instruction in an instruction cache line having a first portion that is cacheable, a second portion that is from a page that is non-cacheable, and crosses a cache line is prevented from executing from the instruction cache. An attribute associated with the non-cacheable second portion is tracked separately from the attributes of the rest of the instructions in the cache line. If the page crossing instruction is reached for execution, the page crossing instruction and instructions following are flushed and a non-cacheable request is made to memory for at least the second portion. Once the second portion is received, the whole page crossing instruction is reconstructed from the first portion saved in the previous fetch group. The page crossing instruction or portion thereof is returned with the proper attribute for a non-cached fetched instruction and the reconstructed instruction can be executed without being cached.

Abstract: Efficient techniques are described for controlling ordered accesses in a weakly ordered storage system. A stream of memory requests is split into two or more streams of memory requests and a memory access counter is incremented for each memory request. A memory request requiring ordered memory accesses is identified in one of the two or more streams of memory requests. The memory request requiring ordered memory accesses is stalled upon determining a previous memory request from a different stream of memory requests is pending. The memory access counter is decremented for each memory request guaranteed to complete. A count value in the memory access counter that is different from an initialized state of the memory access counter indicates there are pending memory requests. The memory request requiring ordered memory accesses is processed upon determining there are no further pending memory requests.

Abstract: Establishing a branch target instruction cache (BTIC) entry for subroutine returns to reduce pipeline bubbles, and related systems, methods, and computer-readable media are disclosed. In one embodiment, a method of establishing a BTIC entry includes detecting a subroutine call in an execution pipeline. In response, at least one instruction fetched sequential to the subroutine call is written as a branch target instruction in a BTIC entry for a subroutine return. A next instruction fetch address is calculated, and is written into a next instruction fetch address field in the BTIC entry. In this manner, the BTIC may provide correct branch target instruction and next instruction fetch address data for the subroutine return, even if the subroutine return is encountered for the first time or the subroutine is called from different calling locations.

Abstract: Fusing immediate value, write-based instructions in instruction processing circuits, and related processor systems, methods, and computer-readable media are disclosed. In one embodiment, a first instruction indicating an operation writing an immediate value to a register is detected by an instruction processing circuit. The circuit also detects at least one subsequent instruction indicating an operation that overwrites at least one first portion of the register while maintaining a value of a second portion of the register. The at least one subsequent instruction is converted (or replaced) with a fused instruction(s), which indicates an operation writing the at least one first portion and the second portion of the register.

Abstract: An instruction in an instruction cache line having a first portion that is cacheable, a second portion that is from a page that is non-cacheable, and crosses a cache line is prevented from executing from the instruction cache. An attribute associated with the non-cacheable second portion is tracked separately from the attributes of the rest of the instructions in the cache line. If the page crossing instruction is reached for execution, the page crossing instruction and instructions following are flushed and a non-cacheable request is made to memory for at least the second portion. Once the second portion is received, the whole page crossing instruction is reconstructed from the first portion saved in the previous fetch group. The page crossing instruction or portion thereof is returned with the proper attribute for a non-cached fetched instruction and the reconstructed instruction can be executed without being cached.

Abstract: A processor includes a conditional branch instruction prediction mechanism that generates weighted branch prediction values. For weakly weighted predictions, which tend to be less accurate than strongly weighted predictions, the power associating with speculatively filling and subsequently flushing the cache is saved by halting instruction prefetching. Instruction fetching continues when the branch condition is evaluated in the pipeline and the actual next address is known. Alternatively, prefetching may continue out of a cache. To avoid displacing good cache data with instructions prefetched based on a mispredicted branch, prefetching may be halted in response to a weakly weighted prediction in the event of a cache miss.

Abstract: Fusing flag-producing and flag-consuming instructions in instruction processing circuits and related processor systems, methods, and computer-readable media are disclosed. In one embodiment, a flag-producing instruction indicating a first operation generating a first flag result is detected in an instruction stream by an instruction processing circuit. The instruction processing circuit also detects a flag-consuming instruction in the instruction stream indicating a second operation consuming the first flag result as an input. The instruction processing circuit generates a fused instruction indicating the first operation generating the first flag result and indicating the second operation consuming the first flag result as the input. In this manner, as a non-limiting example, the fused instruction eliminates a potential for a read-after-write hazard between the flag-producing instruction and the flag-consuming instruction.

Abstract: A processor architecture to qualify software target-branch hints with hardware-based predictions, the processor including a branch target address cache having entries, where an entry includes a tag field to store an instruction address, a target field to store a target address, and a state field to store a state value. Upon decoding an indirect branch instruction, the processor determines whether an entry in the branch target address cache has an instruction address that matches the address of the decoded indirect branch instruction; and if there is a match, depending upon the state value stored in the entry, the processor will use the stored target address as the predicted target address for the decoded indirect branch instruction, or will use a software provided target address hint if available.

Abstract: Embodiments of a data cache are disclosed that substantially decrease a number of accesses to a physically-tagged tag array of the data cache are provided. In general, the data cache includes a data array that stores data elements, a physically-tagged tag array, and a virtually-tagged tag array. In one embodiment, the virtually-tagged tag array receives a virtual address. If there is a match for the virtual address in the virtually-tagged tag array, the virtually-tagged tag array outputs, to the data array, a way stored in the virtually-tagged tag array for the virtual address. In addition, in one embodiment, the virtually-tagged tag array disables the physically-tagged tag array. Using the way output by the virtually-tagged tag array, a desired data element in the data array is addressed.

Abstract: Preventing execution of parity-error-induced unpredictable instructions, and related processor systems, methods, and computer-readable media are disclosed. In this regard, a method for processing instructions in a central processing unit (CPU) is provided. The method comprises decoding an instruction comprising a plurality of bits, and generating a parity error indicator indicating whether a parity error exists in the plurality of bits prior to execution of the instruction. If the parity error indicator indicates that the parity error exists in the plurality of bits, one or more of the plurality of bits are modified to indicate a no execution operation (NOP), without effecting a roll back of a program counter of the CPU and without re-decoding the instruction. In this manner, the possibility of the parity error causing an inadvertent execution of an unpredictable instruction is reduced.

Abstract: The disclosure relates to predicting simple and polymorphic branch instructions. An embodiment of the disclosure detects that a program instruction is a branch instruction, determines whether a program counter for the branch instruction is stored in a program counter filter, and, if the program counter is stored in the program counter filter, prevents the program counter from being stored in a first level predictor.

Abstract: Fusing conditional write instructions having opposite conditions in instruction processing circuits and related processor systems, methods, and computer-readable media are disclosed. In one embodiment, a first conditional write instruction writing a first value to a target register based on evaluating a first condition is detected by an instruction processing circuit. The circuit also detects a second conditional write instruction writing a second value to the target register based on evaluating a second condition that is a logical opposite of the first condition. Either the first condition or the second condition is selected as a fused instruction condition, and corresponding values are selected as if-true and if-false values. A fused instruction is generated for selectively writing the if-true value to the target register if the fused instruction condition evaluates to true, and selectively writing the if-false value to the target register if the fused instruction condition evaluates to false.

Abstract: Systems and methods are disclosed for maintaining an instruction cache including extended cache lines and page attributes for main cache line portions of the extended cache lines and, at least for one or more predefined potential page-crossing instruction locations, additional page attributes for extra data portions of the corresponding extended cache lines. In addition, systems and methods are disclosed for processing page-crossing instructions fetched from an instruction cache having extended cache lines.

Abstract: Eliminating redundant masking operations in instruction processing circuits and related processor systems, methods, and computer-readable media are disclosed. In one embodiment, a first instruction in an instruction stream indicating an operation writing a value to a first register is detected by an instruction processing circuit, the value having a value size less than a size of the first register. The circuit also detects a second instruction in the instruction stream indicating a masking operation on the first register. The masking operation is eliminated upon a determination that the masking operation indicates a read operation and a write operation on the first register and has an identity mask size equal to or greater than the value size. in this manner, the elimination of the masking operation avoids potential read-after-write hazards and improves performance of a CPU by removing redundant operations from an execution pipeline.

Abstract: A Block Normal Cache Allocation (BNCA) mode is defined for a processor. In BNCA mode, cache entries may only be allocated by predetermined instructions. Normal memory access instructions (for example, as part of interrupt code) may execute and will retrieve data from main memory in the event of a cache miss; however, these instructions are not allowed to allocate entries in the cache. Only the predetermined instructions (for example, those used to establish locked cache entries) may allocate entries in the cache. When the locked entries are established, the processor exits BNCA mode, and any memory access instruction may allocate cache entries. BNCA mode may be indicated by setting a bit in a configuration register.

Abstract: The content and order of a predetermined sequence of hard-coded and/or quasi-programmable test patterns may be altered during a Built-In Self-Test (BIST) routine. As such, knowledge gained post design completion may be reflected in the selection and arrangement of available tests to be executed during a BIST routine. In one embodiment, a sequence of hard-coded and/or quasi-programmable tests is executed during a BIST routine by receiving test ordering information for the sequence of tests and executing the sequence of tests in an order indicated by the test ordering information. A corresponding BIST circuit comprises a storage element and a state machine. The storage element is configured to store test ordering information for the sequence of tests. The state machine is configured to execute the sequence of tests in an order indicated by the test ordering information.

Abstract: The disclosure relates to accessing memory content with a high temporal locality of reference. An embodiment of the disclosure stores the content in a data buffer, determines that the content of the data buffer has a high temporal locality of reference, and accesses the data buffer for each operation targeting the content instead of a cache storing the content.

Abstract: Apparatuses and related systems and methods for determining cache hit/miss of aliased addresses in virtually-tagged cache(s) are disclosed. In one embodiment, virtual aliasing cache hit/miss detector for a VIVT cache is provided. The detector comprises a TLB configured to receive a first virtual address and a second virtual address from the VIVT cache resulting from an indexed read into the VIVT cache based on the first virtual address. The TLB is further configured to generate first and second physical addresses translated from the first and second virtual addresses, respectively, The detector further comprises a comparator configured to receive the first and second physical addresses and effectuate a generation of an aliased cache hit/miss indicator based on a comparison of the first and second physical addresses. In this manner, the virtual aliasing cache hit/miss detector correctly generates cache hits and cache misses, even in the presence of aliased addressing.

Abstract: Embodiments of a data cache are disclosed that substantially decrease a number of accesses to a physically-tagged tag array of the data cache are provided. In general, the data cache includes a data array that stores data elements, a physically-tagged tag array, and a virtually-tagged tag array. In one embodiment, the virtually-tagged tag array receives a virtual address. If there is a match for the virtual address in the virtually-tagged tag array, the virtually-tagged tag array outputs, to the data array, a way stored in the virtually-tagged tag array for the virtual address. In addition, in one embodiment, the virtually-tagged tag array disables the physically-tagged tag array. Using the way output by the virtually-tagged tag array, a desired data element in the data array is addressed.