Abstract: For certain classes of software pipelined loops, prologue and epilogue portions of adjacent inner loops in a nested loop can be overlapped. In this way, outer loop code, as well as inner loop code, can be software pipelined. Architectural support for software pipelined nested loops is provided by a set of loop parameter and status registers and by an implementation of loop state dependent, multiway control transfers. For loop body code compatible with two simple constraints, the present invention does not require additional code elements for disabling garbage operations during prologue and epilogue loop periods of adjacent inner loops. Nested loop control allows overlap between the epilogue period of a prior inner loop and the prologue period of a next inner loop. As a result, nested loop code can be more efficiently scheduled by a compiler for execution on a processor such as VLIW processor which provides architectural support for software pipelined nested loops, thereby providing improved loop performance.

Abstract: For certain classes of software pipelined loops, prologue and epilogue control is provided by loop control structures, rather than by predicated execution features of a VLIW architecture. For loops compatible with two simple constraints, code elements are not required for disabling garbage operations during prologue and epilogue loop periods. As a result, resources associated with implementation of the powerful architectural feature of predicated execution need not be squandered to service loop control. In particular, neither increased instruction width nor an increased number of instructions in the loop body is necessary to provide loop control in accordance with the present invention. Fewer service functions are required in the body of a loop. As a result, loop body code can be more efficiently scheduled by a compiler and, in some cases, fewer instructions will be required, resulting in improved loop performance.