IDENTIFYING PAUSIBLE VARIABLE LENGTH MACHINE CODE BY SELECTING ADD- DRESSES IN NUMERICAL SEQUENCE,DECODING CODE STRINGS,AND FOLLOWING EXE- CUTION TRANSFER PATHS

Information about the location of untranslated instructions in an original program is discovered during execution of a partial translation of the program, and that information is used later during re-translation of the original program. Preferably the information includes origin addresses of translated instructions and corresponding destination address of untranslated instructions of execution transfers that occur during the execution of the partial translation. Preferably this feedback of information from execution to re-translation is performed after each execution of the translated program so that virtually all of the instructions in the original program will eventually be located and translated. To provide an indication of the fraction of the code that has been translated, the program is scanned to find plausible code in the areas of memory that do not contain translated code. The plausible code is identified by selecting addresses according to three different scanning modes and attempting to decode variable-length instructions beginning at the selected addresses. The scanning modes include a first mode in which addresses are selected in numerical sequence by a scan pointer, a second mode in which addresses are selected in instruction-length sequence by an instruction decode pointer, and a third mode in which the selected addresses are destination addresses of previously-decoded execution transfer instructions.