Generated Code

Ken Strauss

I've noticed that runtime code is sometimes generated even when everything could be evaluated at compile time. For example:

finishAt VAR Byte
minValue CON 5
finishAt = minValue + 1

Generates runtime code to evaluate (minValue +1). I can code this as:

finishAt VAR Byte
minValue CON 5
finValue CON minValue +1
finishAt = finValue

and avoid the runtime addition but this makes the source code longer and often obscures the intent. Are there any plans to improve SX/B by evaluating constant expressions at compile time? If not, are there other "gotchas" that I can avoid to reduce my code size?

Bean

Ken,
· I'm not sure what you are looking at, but the compiler does genererate the same code as a direct assignment of a constant.
· See the hex code that is generated.

    86  0018  0C06        MOV finishAt,#minValue + 1     ;  finishAt = minValue + 1
        0019  002D
    87                  
    88  001A  0C06        MOV finishAt,#6                ;  finishAt = 6
        001B  002D

Bean.

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There is a fine line between arrogance and confidence. Make sure you don't cross it...

·

Ken Strauss

It works when using byte variables but not with word values. The following:

DEVICE SX28, OSCXT2, TURBO, STACKX, OPTIONX
FREQ 8_000_000

minValue CON 5
minValue4 CON minValue -4
finishAt VAR Word


Program Start

Start:
finishAt = minValue -4

finishAt = minValue4


Compiles to:
MOV finishAt_LSB,#minValue & 255 ;finishAt = minValue -4
MOV finishAt_MSB,#minValue >> 8
SUB finishAt_LSB,#4 & 255
SUBB finishAt_MSB,/C
SUB finishAt_MSB,#4 >> 8


MOV finishAt_LSB,#minValue4 & 255 ;finishAt = minValue4
MOV finishAt_MSB,#minValue4 >> 8