Appendix-C-m3-ziavras

Have completed expensive technique for large

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Unformatted text preview: f instrs. to check for FP exceptions • DEC Alpha 21064 & 21164, IBM Power1 & Power2, MIPS R8000 • Still used in some supercomputers (some exceptions are not permissible or are handled by HW without stopping pipeline) S. Ziavras 4 Techniques (2) 2. Buffer an instr.’s results until all preceding instrs. have completed • Expensive technique for large differences in instr. execution times • 2 variations of this technique variations this technique • History file: keeps track of original reg. values (CYBER 180/190). VAX: for autoincrement and autodecrement addressing • Future file: keeps newer value of a reg. (when all earlier instrs. have completed, future file is earlier instrs. have completed, future file is copied into main reg. file). PowerPC 620, MIPS R10000 extend this variation S. Ziavras 4 Techniques (3) 3. Permit somewhat imprecise exceptions but keep enough info. for trap-handling routines to derive precise info. (having list of instructions in the pipeline and their PCs). After exception handling, software completes any instructions that precede the latest instruction completed and the sequence restarts. – SPARC 4. Hybrid technique: continues with instruction issue technique continues with instruction issue only if it is known that all instructions that precede the issuing instruction will complete without an exception exception. – MIPS R2000/3000 & R4000, Intel Pentium S. Ziavras...
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