On Wed, May 11, 2022 at 1:46 AM RICHU NORMAN <richunor...@cusat.ac.in> wrote: > > Hi, > I am new in gcc development and I am focusing on cross-compilers.I have > added a few instructions for the target machine in binutils and invoked it > using asm() from c program.Now I want to add those instructions to gcc and > define that instruction in target.md file.I have a few queries regarding > the working of gcc.
You might find the GCC introduction at the GCC Resource Center at IIT Bombay of assistance: https://www.cse.iitb.ac.in/grc/ Also, please see the description of the GCC Machine Description https://gcc.gnu.org/onlinedocs/gccint/Machine-Desc.html#Machine-Desc > 1. Do *target.md* files along with* target.cc/.c <http://target.cc/.c> *files > help to invoke assembly instructions automatically? The machine description (MD file, C file and headers) describe the processor (as well as the ABI and other details for the target platform supported by the processor). > 2.What is the input for this ?(.gimple or .cfg files) The machine description is not an independent program that takes input from a file. The GCC compiler runs the various passes, including the ones derived from the information in the MD files. > 3.How does it work internally? > 4.I have defined an instruction in target.md alone.But that does not > work.How to make it work? Please see the documentation linked above and try to understand how the other patterns in the MD file that you modified work. You need to ensure that the pattern you added corresponds to valid RTL that is generated in the port. At a very simplistic level, GCC invokes well-known, named patterns in the MD file to generate RTL, transforms and optimizes the RTL both with generic optimizations and optimizations described in the MD files, and then re-recognizes the RTL to match patterns in the MD file to determine which assembly language to generate. > 5.What is the use of target.c file and how cost is computed in it? > 6.Which file to be examined in rtl-dump of object file for getting the > input and output to this stage in gcc? https://gcc.gnu.org/onlinedocs/gcc/Developer-Options.html#Developer-Options You probably want to use -fdump-rtl-all and see if the expected RTL for your new pattern ever is generated or where it is being lost. Or maybe your pattern is not expecting the canonical form of the RTL into which it is transformed. You need to learn more about the basic internals of GCC. The GCC community can help answer technical questions but cannot debug your machine description changes for you. Thanks, David
