[sdcc-devel] [ sdcc-Bugs-995347 ] Waste mov in GenCast

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Bugs item #995347, was opened at 2004-07-21 18:14
Message generated for change (Comment added) made by maartenbrock
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Category: None
Group: None
Status: Closed
Resolution: None
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: Waste mov in GenCast

Initial Comment:
SDCC codegeneration error:

Source:
#include <8051.h>

static unsigned int work1;

void test(unsigned char arg1, unsigned char arg2)
{
 register unsigned int tmp1;
 //Waste mov in typecasting!
 tmp1=arg1 << 8;
 tmp1|=arg2;
 work1=tmp1;
}

void main(void)
{
test(7,3);
}

SDCC run command:

sdcc --verbose --model-small --peep-asm -mmcs51 --
iram-size 256 
--xram-size 0 --code-size 12288 --nojtbound test.c

SDCC version:

SDCC : 
mcs51/gbz80/z80/avr/ds390/pic16/pic14/TININative/xa51
/ds400/hc08 2.4.2 (Jul 16 2004) (MINGW32)

Asm list:
                            306 ;------------------------------
------------------------------
                            307 ;Allocation info for local 
variables in function 'test'
                            308 ;------------------------------
------------------------------
                            309 ;arg2                      Allocated 
with name '_test_PARM_2'
                            310 ;arg1                      Allocated 
to registers r2 
                            311 ;tmp1                      Allocated 
to registers r2 r3 
                            312 ;------------------------------
------------------------------
                            313 ;test.c:5: void test(unsigned 
char arg1, unsigned char arg2)
                            314 ;	---------------------------
--------------
                            315 ;	 function test
                            316 ;	---------------------------
--------------
   0031                     317 _test:
                    0002    318 	ar2 = 0x02
                    0003    319 	ar3 = 0x03
                    0004    320 	ar4 = 0x04
                    0005    321 	ar5 = 0x05
                    0006    322 	ar6 = 0x06
                    0007    323 	ar7 = 0x07
                    0000    324 	ar0 = 0x00
                    0001    325 	ar1 = 0x01
                            326 ;     genReceive
   0031 AA 82               327 	mov	r2,dpl
                            328 ;test.c:9: tmp1=arg1 << 8;
                            329 ;     genCast
-------------------------------------------------------
---
   0033 7B 00               330 	mov	r3,#0x00 
		Waste mov!
-------------------------------------------------------
---
                            331 ;     genLeftShift
                            332 ;     genLeftShiftLiteral
                            333 ;     genlshTwo
-------------------------------------------------------
---
0035 8A 03               334 	mov	ar3,r2 
0037 7A 00               335 	mov	r2,#0x00
-------------------------------------------------------
---
                            336 ;test.c:10: tmp1|=arg2;
                            337 ;     genCast
   0039 AC*00               338 	mov
	r4,_test_PARM_2
   003B 7D 00               339 	mov	r5,#0x00
                            340 ;     genOr
   003D EC                  341 	mov	a,r4
   003E 4A                  342 	orl	a,r2
   003F F5*00               343 	mov	_work1,a
   0041 ED                  344 	mov	a,r5
   0042 4B                  345 	orl	a,r3
   0043 F5*01               346 	mov	(_work1 
+ 1),a
                            347 ;test.c:11: work1=tmp1;
   0045                     348 00101$:
   0045 22                  349 	ret


I'm fix this bug by peephole rule:
replace {
mov %1,%2
mov a%1,%3
} by {
; peephole r.1
mov a%1,%3
}




----------------------------------------------------------------------

>Comment By: Maarten Brock (maartenbrock)
Date: 2004-07-26 12:16

Message:
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user_id=888171

Unfortunately that is not the instruction you throw away. It's 
mov r%1,%2 in your fix. That could very well be MOV 
Rn,direct. Any SFR will do here as %2 !

----------------------------------------------------------------------

Comment By: Frieder Ferlemann (frief)
Date: 2004-07-26 11:55

Message:
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user_id=589052

Hi Maarten,

no it should be OK. No SDCC generated symbol (save for acc)
matches mov a%1, (unless I'm mistaken that is)

Frieder


----------------------------------------------------------------------

Comment By: Maarten Brock (maartenbrock)
Date: 2004-07-26 11:30

Message:
Logged In: YES 
user_id=888171

Frieder,

Shouldn't you check some volatileness here before throwing 
away a read instruction on %2 ?

Maarten

----------------------------------------------------------------------

Comment By: Frieder Ferlemann (frief)
Date: 2004-07-26 00:32

Message:
Logged In: YES 
user_id=589052

added contributed fix for "bug" #995347 as peephole 177.e. 
Thanks to anonymous! 

----------------------------------------------------------------------

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