The translator is used to convert an assembly language file produced by the VLIW compiler into the assembly language of an existing architecture, in this case, an RS/6000. Since the VLIW compiler generates tree-instructions, extra RS/6000 instructions must be added to simulate the effect of a tree. In essence, a set of RS/6000 branches are placed before the ALU operations from each segment of a tree. In addition, the VLIW architecture has more registers than the RS/6000, necessitating that VLIW registers normally be kept in memory, then temporarily loaded them into RS/6000 registers to perform specific ALU operations, with the result stored back to the appropriate VLIW register in memory. This is most complicated for non-general purpose registers, such as the Condition Code register which can be addressed as individual bits, as 4-bit groups, or as a full register. To accomodate these different modes of access, a great deal of shifting and masking must be performed.

Statistics are needed to analyze the performance of the VLIW architecture and compiler. For these purposes, the translator places counting instructions at each tree path in the corresponding RS/6000 code. It also writes an annotation file describing each tree-instruction and tree-path. When a program finishes execution, its counters are flushed to disk. A postpass routine then combines the information from the counts file and the annotation file to find (1) the total number of times each instruction and path was executed, (2) the mean parallelism achieved, (3) the dynamic distribution of different opcode frequencies, and (4) other statistics. The postpass routine is also used to generate profile-directed feedback information for the VLIW compiler.

A number of other issues must be addressed to make the translator perform correctly. For example, interfaces to standard shared libraries such as "malloc", "qsort", and "setjmp" must be correct. In the case of "qsort," provision must be made for the library to call a VLIW comparison routine, while "setjmp" must be modified to handle VLIW registers instead of RS/6000 registers. Some means of debugging both the compiled program produced by the VLIW compiler and the correctness of the translator's code is also essential. We addressed this problem by using dbx macros to define VLIW debug commands.