[SPL] Static Subexpression Elimination

[Clifford Wolf]

Hi,

the optimizer in the SPL compiler can do static subexpression elimination
now (subversion rev. 615, it is not part of todays snapshot). E.g.:

	debug "This is a ${ "lit"~"tle" } test: ${ (3+4+5)*4 - 6 }";

This script is compiled to the following SPL assembler code if the
optimizer is used:

	$ ./splrun -AN demo.spl
	# SPL Assembler Dump
	:16     PUSHC       "This is a little test: 42" # (1 byte arg) 0
	:18     DEBUG
	:19     HALT
	# Total size: 30 bytes (4 text, 26 data).

The unoptimized assembler code looks like this:

	$ ./splrun -oAN demo.spl
	# SPL Assembler Dump
	:16     PUSHC       "This is a "     # (4 byte arg) 0
	:21     PUSHC       "lit"            # (4 byte arg) 11
	:26     PUSHC       "tle"            # (4 byte arg) 15
	:31     CAT
	:32     CAT
	:33     PUSHC       " test: "        # (4 byte arg) 19
	:38     CAT
	:39     PUSHC       "3"              # (4 byte arg) 27
	:44     PUSHC       "4"              # (4 byte arg) 29
	:49     IADD
	:50     PUSHC       "5"              # (4 byte arg) 31
	:55     IADD
	:56     PUSHC       "4"              # (4 byte arg) 29
	:61     IMUL
	:62     PUSHC       "6"              # (4 byte arg) 33
	:67     ISUB
	:68     CAT
	:69     PUSHC       ""               # (4 byte arg) 10
	:74     CAT
	:75     DEBUG
	:76     HALT
	# Total size: 96 bytes (61 text, 35 data).

I think more optimization can't be expected from a scripting language
compiler..  ;-)

Please let me know if you encounter any problems or strange behavior with
the optimizer enabled. I have done my best to implement it bugfree and test
it well, but nobody is perfect - especially when writing compilers.

yours,
 - clifford

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