International Business Machines Corporation

Stephen J Ciavaglia

James Henry Hesson

Jay LeBlanc

Paul David Kartschoke

Stephen William Mahin

Stephen Emery Rich

Lyman Henry Moulton, Iii

Stephen Michael Conor

Pamela Anne Wilcox

Walter Thomas Esling

An apparatus performs source operand dependency analysis, perform register renaming and provide rapid pipeline recovery for a microprocessor capable of issuing and executing multiple instructions out-of-order in a single machine cycle. The apparatus first provides an enhanced means for rapid pipeline recovery due to a mispredicted branch or other store/load conflict or unsupported store/load forward circumstances. Second, the apparatus provides an improved instruction scheduling means wherein the oldest instructions that have all of their dependencies resolved are executed first. Third, the apparatus provides a means for enabling any execution or memory access instruction to execute out-of-order. Fourth, the apparatus provides a means for handling precise recovery of interrupts when processing instructions in out-of-order sequence.

Apparatus to perform source operand dependency analysis perform register

An apparatus to dynamically controls the out-of-order execution of load/store instructions by detecting a store violation condition and avoiding the penalty of a pipeline recovery process. The apparatus permits a load and store instruction to issue and execute out of order and incorporates a unique store barrier cache which is used to dynamically predict whether or not a store violation condition is likely to occur and, if so, to restrict the issue of instructions to the load/store unit until the store instruction has been executed and it is once again safe to proceed with out-of-order execution. The method implemented by the apparatus delivers performance within one percent of theoretically possible with apriori knowledge of load and store addresses.

Apparatus to dynamically control the out-of-order execution of

A mechanism which manages variable length instructions in cache is comprised of three cooperating elements designed to optimize self modifying code and anticipate next instructions for branch operand management. A content addressable memory (CAM) stores addresses of lines which have been accessed for instruction fetching. In a system having modifiable instruction stream (i.e., store to instruction stream), when the CAM matches, the system must retire certain instructions, flush instructions and then fetch the modified instruction stream. Boundary identification logic examines a field in each cache byte to determine the nature of the byte. This field is initially cleared at the time the cache line is loaded and filled with the line is fetched. An anticipation buffer designed to minimize the circuitry necessary for fetches across cache lines is loaded with sequentially anticipated prefetched instructions from the cache. These anticipated instructions can then be concatenated by a fetch aligner.

Superscaler instruction pipeline having boundary identification logic

Superscaler instruction pipeline having boundary indentification logic

Apparatus for source operand dependendency analyses register renaming

Superscalar instruction pipeline using alignment logic responsive to

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Chittenden County, VT, United States of America

Stephen J Ciavaglia