[sdcc-devel] [ sdcc-Feature Requests-1475742 ] Braindead bit-test handling with == 0

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Feature Requests item #1475742, was opened at 2006-04-24 21:25
Message generated for change (Comment added) made by bernhardheld
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>Category: None
>Group: None
>Status: Open
>Priority: 3
Submitted By: Stevie Oh (stevie-o)
>Assigned to: Bernhard Held (bernhardheld)
Summary: Braindead bit-test handling with == 0

Initial Comment:
I apologize in advance if this should really be a
feature request/enhancement.

==Summary==

The translation of a single-bit test to a BTFSS/BTFSC
instruction is not all that smart:

 ;	.line	9; btfssdumb.c	if (!(PORTB & BIT_5)) { foo(); }
 	BTFSC	_PORTB, 5
 	GOTO	_00106_DS_
 	CALL	_foo

That works fine. But this perfectly valid alternate
syntax fails miserably:

 ;	.line	10; btfssdumb.c	if ((PORTB & BIT_5) == 0) {
bar(); }
 	MOVLW	0x20
 	ANDWF	_PORTB, W
 	MOVWF	r0x00
 	MOVF	r0x00, W
 	BNZ	_00114_DS_
 	GOTO	_00115_DS_

==SDCC Version==

SDCC :
mcs51/gbz80/z80/avr/ds390/pic16/pic14/TININative/xa51/ds400/hc08
2.5.6 #1249 (Apr 17 2006) (MINGW32)

==Command Line==

sdcc -mpic16 -p18f452 btfssdumb.c

==Other Information==

Attached is a tar.bz2 of all the files involved.

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>Comment By: Bernhard Held (bernhardheld)
Date: 2006-04-24 23:03

Message:
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Well, the code could be even more worse ;-) Obviously the 
promotion to int has been suppressed. At the moment sdcc 
compares two 'unsigned char'.
It's not that easy to fit the promotion rules and bit 
banging together, but I see a chance to optimize this case.
Let's make a feature request out of it.

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Comment By: Raphael Neider (tecodev)
Date: 2006-04-24 22:32

Message:
Logged In: YES 
user_id=1115835

I am no expert in these questions (ask Bernhard Held ;-)),
but this should be due to the all-famous C promotion rules:
Comparing a bit(field) and an integer probably requires an
upcast to int (at least to char it seems), so...

This will not be fixed (unless I am proven wrong, that is).

Regards,
Raphael


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