Register Allocation and Experiments

Using oatc

oatc acts like the clang compiler. Given several .oat, .ll, .c, and .o files, it will compile the .oat and .ll files to .s files and then combine the results with the .c and .o files to produce an executable named a.out. You can also compile the .ll files using clang instead of the current backend, which can be useful for testing purposes.

• To run the automated test harness do:

    ./oatc --test
  

• To compile oat files using the backend:

    ./oatc path/to/foo.oat
  

  • creates output/foo.ll frontend ll code
  • creates output/foo.s backend assembly code
  • creates output/foo.o assembled object file
  • creates a.out linked executable

NOTE: by default the .s and .o files are created in a directory called output, and the filenames are chosen so that multiple runs of the compiler will not overwrite previous outputs. foo.ll will be compiled first to foo.s then foo_1.s, foo_2.s, etc.

• To compile oat files using the clang backend:

    ./oatc --clang path/to/foo.oat
  

• Useful flags:

  Flag	Description
  --regalloc {none,greedy,better}	use the specified register allocator
  --liveness {trivial,dataflow}	use the specified liveness analysis
  --print-regs	prints the register usage statistics for x86 code
  --print-oat	pretty prints the Oat abstract syntax to the terminal
  --print-ll	echoes the ll program to the terminal
  --print-x86	echoes the resulting .s file to the terminal
  --interpret-ll	runs the ll file through the reference interpreter and outputs the results to the console
  --execute-x86	runs the resulting a.out file natively (applies to either our backend or clang-compiled code)
  --clang	compiles to assembly using clang, not the current backen
  -v	generates verbose output, showing which commands are used for linking, etc.
  -op <dirname>	change the output path [DEFAULT=output]
  -o	change the generated executable's name [DEFAULT=a.out]
  -S	stop after generating .s files
  -c	stop after generating .o files
  -h or --help	display the list of options

• Example uses:

Run the test case hw4programs/fact.oat using the backend:

      ./oatc --execute-x86 hw4programs/fact.oat bin/runtime.c
      120--------------------------------------------------------------- Executing: a.out
      * a.out returned 0