Digital Equipment Corporation

Steven O Hobbs

Michael C Adler

Paul Geoffrey Lowney

Dileep P Bhandarkar

Kevin W Harris

Robert M Supnik

William B Noyce

Robert Neil Faiman, Jr

David S Blickstein

Hai Huang

Curt K Burmeister

Caroline S Davidson

Richard B Grove

Methods for handling exceptions caused by speculatively scheduled instructions or predicated instructions executed within a computer program are described. The method for speculatively scheduled instructions includes checking at a commit point of a speculatively scheduled instruction, a semaphore associated with the speculatively scheduled instruction and branching to an error handling routine if the semaphore is set. A set semaphore indicates that an exception occurred when the speculatively scheduled instruction was executed. For a predicated instruction the method includes checking a predicate of an eliminated branch and a semaphore associated with the speculative instruction at a commit point of the speculative instruction and branching to an error handling routine if the semaphore indicates that an exception occurred when said speculative instruction was executed, and the predicate is true, which indicates that said speculative instruction was properly executed.

Software mechanism for accurately handling exceptions generated by

Methods for handling exceptions caused by speculatively scheduled instructions or predicated instructions executed within a computer program are described. The method for speculatively scheduled instructions includes checking at a commit point of a speculatively scheduled instruction, a semaphore associated with the speculatively scheduled instruction and branching to an error handling routine in the semaphore is set. A set semaphore indicates that an exception occurred when the speculatively scheduled instruction was executed. For a predicated instruction the method includes checking a predicate of a eliminated branch and a semaphore associated with the speculative instruction at a commit point of the speculative instruction and branching to an error handing routine if the semaphore indicates that an exception occurred when the speculative instruction was executed, and the predicate is true, which indicates that the speculative instruction was properly executed.

A compiler framework uses a generic 'shell' and a generic back end (where the code generator is target-specific). The generic back end provides the functions of optimization, register and memory allocation, and code generation. The code generation function of the back end may be targeted for any of a number of computer architectures. A front end is tailored for each different source language, such as Cobol, Fortran, Pascal, C, C++, etc. The front end scans and parses the source code modules, and generates from them an intermediate language representation of the source code programs expressed in the source code. The intermediate language represents any of the source code languages in a universal manner, so the interface between the front end and back end is of a standard format, and need not be rewritten for each language-specific front end. A feature is a method for doing code generation using code templates in a multipass manner. The selection and application of code templates occurs at four different times during the compilation process: (1) A pattern select phase does a pattern match in a context pass to select the best code templates; (2) Tasks of the context pass use context actions of the selected templates to analyze the evaluation order to expressions and to allocate temporary names; (3) A bind pass uses the binding actions of the selected templates to allocate template names; (4) Finally, a code pass uses code generation actions of the selected templates to guide the generation of object code.

Optimizing compiler using templates corresponding to portions of an

A compiler framework uses a generic 'shell' and a generic back end (where the code generator is target-specific). The generic back end provides the functions of optimization, register and memory allocation, and code generation. The code generation function of the back end may be targeted for any of a number of computer architectures. A front end is tailored for each different source language, such as Cobol, Fortran, Pascal, C, C++, etc. The front end scans and parses the source code modules, and generates from them an intermediate language representation of the source code programs expressed in the source code. The intermediate language represents any of the source code languages in a universal manner, so the interface between the front end and back end is of a standard format, and need not be rewritten for each language-specific front end. A feature is a mechanism for representing effects and dependencies in the interface between front end and back end. An element has an effect if it writes to memory, and has a dependency if it reads from a location which some other node may write to. A mechanism which is independent of source language is provided for describing the effects of program execution.

Compiler back end calling predetermined front end routines that use

A compiler includes a register allocation method making use of the concept of assigning temporary items to lifetime holes if such holes exist that are suitable. The compiler includes a front end for converting the input code to an intermediate representation, then this input representation is traversed to identify all of the temporary items, and to find all of the holes in the temporary items. Lists are maintained of the identified temporaries and holes. Register allocation then includes assigning temporaries to registers so long as there are free registers, and if holes are available in already-assigned temporaries then these holes are used in assigning registers. After all the available registers and holes are used, remaining temporaries are unallocated and thus represent memory references.

Compiler allocating a register to a data item used between a use and

Save-Exception-State and Restore-Exception-State primitives are defined in the operating system and are used to confine the reporting of delayed asynchronous coprocessor exceptions to the respective code threads that generate the exceptions. The Save-Exception-State primitive saves the coprocessor exception state pertinent to the currently executed code thread, and the Restore-Exception-State primitive restores a selected one of the exception states having been saved. The Save-Exception-State primitive synchronizes the coprocessor, disables use of the coprocessor, saves any pending coprocessor exception state into memory, and clears the coprocessor exception state information from the coprocessor or a 'thread descriptor' area of memory allocated to the current code thread. The Restore-Exception-State primitive synchronizes the coprocessor, disables use of the coprocessor, reports any pending exceptions in the coprocessor, and restores the saved exception state into a respective code thread descriptor in memory allocated to the code thread having generated the saved exception state information. The restored exception state is reported by a 'Coprocessor-Disabled' exception handler that checks for any exceptions pending in the coprocessor or thread descriptor, when necessary stores the coprocessor state information from the process which last executed a coprocessor instruction, when necessary retrieves the coprocessor state information for the current process, reports any pending exceptions, and reenables use of the coprocessor.

Reporting delayed coprocessor exceptions to code threads having caused

A data process system capable of executing vector instructions and scalar instructions detects the occurrence of arithmetic exception conditions and allows subsequent scalar instruction processing until execution of the next vector instruction is required.

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Westford, MA, United States of America

Steven O Hobbs