The zcc command automatically involves the copt optimizer. The level of optimization is defined by the “-O<n>” flag, in which <n> defines the number of passes and consequently the quantity of rules wich will be applied.

The optimization level is '2', but raising to '3' shouldn't have negative effects at all:

      zcc -O3 [flags]  [files to be compiled/linked]

Excluding the optimizer (-O0) is normally a bad idea.

The ruleset files are located in:

      {z88dk}/lib/z80rules.2
      {z88dk}/lib/z80rules.1
      {z88dk}/lib/z80rules.0

Every rule is separated by a blank line. Then a number of 'matching lines' is defined along with a 'transformed block, separated by the equal sign:

	ld	hl,%1	;const
	ld	(%2),hl
	ld	hl,0	;const
=
	ld	hl,%1	;const
	ld	(%2),hl

The compiler generated code includes comments which help the rules avoiding to be too aggressive.

	jr	z,ASMPC+3
	scf
	call	c,%2
=
	call	nz,%2