sqlite/mkopcodeh.awk

#!/usr/bin/awk -f
#
# Generate the file opcodes.h.
#
# This AWK script scans a concatenation of the parse.h output file from the
# parser and the vdbe.c source file in order to generate the opcodes numbers
# for all opcodes.  
#
# The lines of the vdbe.c that we are interested in are of the form:
#
#       case OP_aaaa:      /* same as TK_bbbbb */
#
# The TK_ comment is optional.  If it is present, then the value assigned to
# the OP_ is the same as the TK_ value.  If missing, the OP_ value is assigned
# a small integer that is different from every other OP_ value.
#
# We go to the trouble of making some OP_ values the same as TK_ values
# as an optimization.  During parsing, things like expression operators
# are coded with TK_ values such as TK_ADD, TK_DIVIDE, and so forth.  Later
# during code generation, we need to generate corresponding opcodes like
# OP_Add and OP_Divide.  By making TK_ADD==OP_Add and TK_DIVIDE==OP_Divide,
# code to translate from one to the other is avoided.  This makes the
# code generator run (infinitesimally) faster and more importantly it makes
# the library footprint smaller.
#
# This script also scans for lines of the form:
#
#       case OP_aaaa:       /* no-push */
#
# When the no-push comment is found on an opcode, it means that that
# opcode does not leave a result on the stack.  By identifying which
# opcodes leave results on the stack it is possible to determine a
# much smaller upper bound on the size of the stack.  This allows
# a smaller stack to be allocated, which is important to embedded
# systems with limited memory space.  This script generates a series
# of "NOPUSH_MASK" defines that contain bitmaps of opcodes that leave
# results on the stack.  The NOPUSH_MASK defines are used in vdbeaux.c
# to help determine the maximum stack size.
#


# Remember the TK_ values from the parse.h file
/^#define TK_/ {
  tk[$2] = $3
}

# Scan for "case OP_aaaa:" lines in the vdbe.c file
/^case OP_/ {
  name = $2
  sub(/:/,"",name)
  sub("\r","",name)
  op[name] = -1
  for(i=3; i<NF; i++){
    if($i=="same" && $(i+1)=="as"){
      sym = $(i+2)
      sub(/,/,"",sym)
      op[name] = tk[sym]
      used[op[name]] = 1
      sameas[op[name]] = sym
    }
    if($i=="no-push"){
      nopush[name] = 1
    }
  }
}

# Assign numbers to all opcodes and output the result.
END {
  cnt = 0
  max = 0
  print "/* Automatically generated.  Do not edit */"
  print "/* See the mkopcodeh.awk script for details */"
  for(name in op){
    if( op[name]<0 ){
      cnt++
      while( used[cnt] ) cnt++
      op[name] = cnt
    }
    used[op[name]] = 1;
    if( op[name]>max ) max = op[name]
    printf "#define %-25s %15d", name, op[name]
    if( sameas[op[name]] ) {
      printf "   /* same as %-12s*/", sameas[op[name]]
    } 
    printf "\n"

  }
  seenUnused = 0;
  for(i=1; i<max; i++){
    if( !used[i] ){
      if( !seenUnused ){
        printf "\n/* The following opcode values are never used */\n"
        seenUnused = 1
      }
      printf "#define %-25s %15d\n", sprintf( "OP_NotUsed_%-3d", i ), i
    }
  }

  # Generate the 10 16-bit bitmasks used by function opcodeUsesStack()
  # in vdbeaux.c. See comments in that function for details.
  # 
  nopush[0] = 0              # 0..15
  nopush[1] = 0              # 16..31
  nopush[2] = 0              # 32..47
  nopush[3] = 0              # 48..63
  nopush[4] = 0              # 64..79
  nopush[5] = 0              # 80..95
  nopush[6] = 0              # 96..111
  nopush[7] = 0              # 112..127
  nopush[8] = 0              # 128..143
  nopush[9] = 0              # 144..159
  for(name in op){
    if( nopush[name] ){
      n = op[name]
      j = n%16
      i = ((n - j)/16)
      nopush[i] = nopush[i] + (2^j)
    }
  }
  printf "\n"
  print "/* Opcodes that are guaranteed to never push a value onto the stack"
  print "** contain a 1 their corresponding position of the following mask"
  print "** set.  See the opcodeNoPush() function in vdbeaux.c  */"
  for(i=0; i<10; i++){
    printf "#define NOPUSH_MASK_%d 0x%04x\n", i, nopush[i]
  }
}