Hi, RTV/N instruction is one of the new instructions added in the SH2A target.
Description : RTV/N instruction performs a return from a subroutine procedure after a transfer from specified general register Rn to R0. That is, after the Rn value is stored in R0, the PC is restored from PR, and processing is resumed from the address indicated by the PC. RTV/N Rn = Rn--->R0 + RTS/N So RTV/N instruction can be used as an optimized return instruction in case of the functions having the return type as INTEGER_TYPE. This instruction moves the return argument of the function from register Rn--->R0 along with RETURN. So there is no need to exclusively transfer the RETURN value of the function to RETURN_REG (R0) before RETURN. We implemented the direct RTL for RTV/N instruction and found that the RTL is not recognized by the GNUSH compiler. It was because the return value is moved from the register Rn--->R0 before the epilogue sequence and RETURN is performed after the epilogue sequence. As the observation goes, all the architectures as incorporated in GCC transfers the RETURN value of a function to RETURN_REG (Rn--->R0) before the epilogue sequence followed by RETURN. We investigated and found that the register transfer Rn--->R0 is done in the top level file "gcc/stmt.c". The function where this transfer is done is expand_value_return (rtx val). RTV/N instruction requires this transfer to be suppressed and using the register Rn in RETURN pattern as "RTV/N Rn". Implementation : We tried to get the register (Rn) transferred to RETURN_REG(R0) from the function expand_value_return (rtx val). This register Rn needs to be used as the operand in "RTV/N Rn" instruction. However register (Rn) in the function expand_value_return (rtx val) is a PSEUDO REGISTER instead of a HARD REGISTER. "RTV/N Rn" expects the register Rn to be a hard register. Any help in implementing this instruction would be highly appreciated. Regards, Naveen.H.S. KPIT Cummins Infosystems Ltd, Pune (INDIA) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Free download of GNU based tool-chains for Renesas' SH, H8, R8C, M16C and M32C Series. The following site also offers free technical support to its users. Visit http://www.kpitgnutools.com for details. Latest versions of KPIT GNU tools were released on June 1, 2007. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
