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Missing Optimisations

Heap check hoisting

Unnecessary evals

Consider the function:

 infList :: Int -> List Int
 infList n =
   let l1 = Cons n l2; l2 = Cons n l1 in l1

The generated code currently looks like this:

    alloc_frame 3
0   r1 = <blackhole>
1   r2 = &Cons_con_info
2   r1 = alloc(r2, r0, r1)
3   r0 = alloc(r2, r0, r1)
4   Mem[r1 + 2] = r0
5   eval r0 {r0}
6   return r0

Note the eval at instruction 5. We know that r0 has constructor Cons because we just allocated it, so the call to eval will return immediately and can be removed.

Trace Selection

  • How much polymorphism is introduced by EVAL?

  • Should we specialise per call-site rather than per function?

  • Use traces at all, or use some hybrid scheme?

Benchmarks

  • Are micro-benchmarks enough?

  • A compiler (or type checker) could be interesting -- lots of nested case expressions. This is a good test whether trace sizes can become large.

Code generation

There are a lot of special cases for the SAVE instruction. We do need something like it for unrolled traces with increasing or decreasing stack. However, there can only ever be one SAVE per trace, so we could store it in the IR buffer or assembler state instead and always create an automatic snapshot at the end.

Configuration

The following configure.in lines should allow detecting the LEADING_UNDERSCORE feature.

#######################
## test for underscores. The vpi module loader in vvm needs to know this
## in order to know the name of the start symbol for the .vpi module.
#######################

AC_MSG_CHECKING("for leading and/or trailing underscores")
cat << EOF > underscore.c
       void underscore(void){}
EOF
$CC -c underscore.c > /dev/null 2>&1

CC_LEADING_UNDERSCORE=no
CC_TRAILING_UNDERSCORE=no

output=`nm underscore.o|grep _underscore 2>&1`
if test ! -z "$output"; then
  CC_LEADING_UNDERSCORE=yes
  AC_DEFINE(NEED_LU)
fi

output=`nm underscore.o|grep underscore_ 2>&1`
if test ! -z "$output"; then
  CC_TRAILING_UNDERSCORE=yes
  AC_DEFINE(NEED_TU)
fi

if test "$CC_LEADING_UNDERSCORE" = yes; then
  AC_DEFINE(WLU)
fi
if test "$CC_TRAILING_UNDERSCORE" = yes; then
  AC_DEFINE(WTU)
fi

rm underscore.c underscore.o

AC_MSG_RESULT("$CC_LEADING_UNDERSCORE $CC_TRAILING_UNDERSCORE")

#######################
## end of test for underscores
#######################

From https://github.com/freequaos/sourcenavigator/blob/cb99d9a17/snavigator/parsers/verilog/configure.in