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[avr-gcc-list] Optimization problems
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From: |
Tvrtko A. Ursulin |
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Subject: |
[avr-gcc-list] Optimization problems |
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Date: |
Thu, 10 Oct 2002 10:16:34 +0200 |
Hello everyone!
This is my first posting to this list, and not only that, I have only recently
started coding in avr-gcc.
I downloaded avr-gcc patch which applied cleanly to gcc 3.0.4.
I wrote a small kernel for a exercise. Mostly in C with small asm parts.
Everything works ok when compiled without -O, but with any -O tested (-Os, -O,
-O2, -O9) it fails to store global variable back to RAM after manipulating
it.
To clarify a bit. Below is the source code of two tasks that should run under
my kernel. They don't do much, just run forever, and kernel preempts them,
and gives control to other one.
They manipulate a global variable "gval" (at RAM 0x60), but with any
optimization turned on, they never store that variable back in RAM. I suppose
that is because the compiler sees it is a endless loop and thinks there is no
point in doing that.
But I would really like to find out a way to solve this, because all my future
tasks will be endless loops also, and code generated without optimizations is
really suboptimal. As you can see in below asm listing... :(
Many thanks for any help!
--------------------------------------------------------------------
source.c
--------------------------------------------------------------------
void task1(void) __attribute__((naked));
void task2(void) __attribute__((naked));
uint8_t gval = 0x08;
void task1(void)
{
outp(0xff,DDRB);
for (;;)
{
gval--;
outp(~gval,PORTB);
}
}
void task2(void)
{
outp(0xff,DDRB);
for (;;)
{
gval++;
outp(~gval,PORTB);
}
}
--------------------------------------------------------------------
compiled with:
avr-gcc -g -mmcu=at90s8515 -Wall -Wstrict-prototypes
--------------------------------------------------------------------
void task1(void)
{
82: cf 93 push r28
84: df 93 push r29
86: cd b7 in r28, 0x3d ; 61
88: de b7 in r29, 0x3e ; 62
outp(0xff,DDRB);
8a: 8f ef ldi r24, 0xFF ; 255
8c: 87 bb out 0x17, r24 ; 23
8e: 00 00 nop
for (;;)
{
gval--;
90: 80 91 60 00 lds r24, 0x0060
94: 81 50 subi r24, 0x01 ; 1
96: 80 93 60 00 sts 0x0060, r24
outp(~gval,PORTB);
9a: 80 91 60 00 lds r24, 0x0060
9e: 80 95 com r24
a0: 88 bb out 0x18, r24 ; 24
a2: f6 cf rjmp .-20 ; 0x90
}
}
a4: df 91 pop r29
a6: cf 91 pop r28
a8: 08 95 ret
000000aa <task2>:
void task2(void)
{
aa: cf 93 push r28
ac: df 93 push r29
ae: cd b7 in r28, 0x3d ; 61
b0: de b7 in r29, 0x3e ; 62
outp(0xff,DDRB);
b2: 8f ef ldi r24, 0xFF ; 255
b4: 87 bb out 0x17, r24 ; 23
b6: 00 00 nop
for (;;)
{
gval++;
b8: 80 91 60 00 lds r24, 0x0060
bc: 8f 5f subi r24, 0xFF ; 255
be: 80 93 60 00 sts 0x0060, r24
outp(~gval,PORTB);
c2: 80 91 60 00 lds r24, 0x0060
c6: 80 95 com r24
c8: 88 bb out 0x18, r24 ; 24
ca: f6 cf rjmp .-20 ; 0xb8
}
}
cc: df 91 pop r29
ce: cf 91 pop r28
d0: 08 95 ret
--------------------------------------------------------------------
compiled with:
avr-gcc -g -mmcu=at90s8515 -Wall -Wstrict-prototypes -Os
--------------------------------------------------------------------
00000082 <task1>:
outp(0xff,DDRB);
82: 8f ef ldi r24, 0xFF ; 255
84: 87 bb out 0x17, r24 ; 23
for (;;)
86: 80 91 60 00 lds r24, 0x0060
8a: 80 95 com r24
{
gval--;
8c: 8f 5f subi r24, 0xFF ; 255
outp(~gval,PORTB);
8e: 88 bb out 0x18, r24 ; 24
90: fd cf rjmp .-6 ; 0x8c
92: 08 95 ret
00000094 <task2>:
outp(0xff,DDRB);
94: 8f ef ldi r24, 0xFF ; 255
96: 87 bb out 0x17, r24 ; 23
for (;;)
98: 80 91 60 00 lds r24, 0x0060
9c: 80 95 com r24
{
gval++;
9e: 81 50 subi r24, 0x01 ; 1
outp(~gval,PORTB);
a0: 88 bb out 0x18, r24 ; 24
a2: fd cf rjmp .-6 ; 0x9e
a4: 08 95 ret
--------------------------------------------------------------------
compiled with:
avr-gcc -g -mmcu=at90s8515 -Wall -Wstrict-prototypes -Os
--------------------------------------------------------------------
00000082 <task1>:
outp(0xff,DDRB);
82: 8f ef ldi r24, 0xFF ; 255
84: 87 bb out 0x17, r24 ; 23
for (;;)
86: 90 91 60 00 lds r25, 0x0060
{
gval--;
8a: 91 50 subi r25, 0x01 ; 1
outp(~gval,PORTB);
8c: 89 2f mov r24, r25
8e: 80 95 com r24
90: 88 bb out 0x18, r24 ; 24
92: fb cf rjmp .-10 ; 0x8a
}
}
94: 08 95 ret
00000096 <task2>:
outp(0xff,DDRB);
96: 8f ef ldi r24, 0xFF ; 255
98: 87 bb out 0x17, r24 ; 23
for (;;)
9a: 90 91 60 00 lds r25, 0x0060
{
gval++;
9e: 9f 5f subi r25, 0xFF ; 255
outp(~gval,PORTB);
a0: 89 2f mov r24, r25
a2: 80 95 com r24
a4: 88 bb out 0x18, r24 ; 24
a6: fb cf rjmp .-10 ; 0x9e
}
}
a8: 08 95 ret
--------------------------------------------------------------------
compiled with:
avr-gcc -g -mmcu=at90s8515 -Wall -Wstrict-prototypes -O2
--------------------------------------------------------------------
outp(0xff,DDRB);
82: 8f ef ldi r24, 0xFF ; 255
84: 87 bb out 0x17, r24 ; 23
for (;;)
86: 90 91 60 00 lds r25, 0x0060
{
gval--;
8a: 89 2f mov r24, r25
8c: 81 50 subi r24, 0x01 ; 1
outp(~gval,PORTB);
8e: 98 2f mov r25, r24
90: 80 95 com r24
92: 88 bb out 0x18, r24 ; 24
94: fa cf rjmp .-12 ; 0x8a
96: 08 95 ret
00000098 <task2>:
outp(0xff,DDRB);
98: 8f ef ldi r24, 0xFF ; 255
9a: 87 bb out 0x17, r24 ; 23
for (;;)
9c: 90 91 60 00 lds r25, 0x0060
{
gval++;
a0: 89 2f mov r24, r25
a2: 8f 5f subi r24, 0xFF ; 255
outp(~gval,PORTB);
a4: 98 2f mov r25, r24
a6: 80 95 com r24
a8: 88 bb out 0x18, r24 ; 24
aa: fa cf rjmp .-12 ; 0xa0
ac: 08 95 ret
--------------------------------------------------------------------
compiled with:
avr-gcc -g -mmcu=at90s8515 -Wall -Wstrict-prototypes -O9
--------------------------------------------------------------------
00000082 <task1>:
outp(0xff,DDRB);
82: 2f ef ldi r18, 0xFF ; 255
84: 27 bb out 0x17, r18 ; 23
for (;;)
86: 90 91 60 00 lds r25, 0x0060
{
gval--;
8a: 29 2f mov r18, r25
8c: 21 50 subi r18, 0x01 ; 1
outp(~gval,PORTB);
8e: 92 2f mov r25, r18
90: 20 95 com r18
92: 28 bb out 0x18, r18 ; 24
94: fa cf rjmp .-12 ; 0x8a
96: 08 95 ret
00000098 <task2>:
outp(0xff,DDRB);
98: 2f ef ldi r18, 0xFF ; 255
9a: 27 bb out 0x17, r18 ; 23
for (;;)
9c: 90 91 60 00 lds r25, 0x0060
{
gval++;
a0: 29 2f mov r18, r25
a2: 2f 5f subi r18, 0xFF ; 255
outp(~gval,PORTB);
a4: 92 2f mov r25, r18
a6: 20 95 com r18
a8: 28 bb out 0x18, r18 ; 24
aa: fa cf rjmp .-12 ; 0xa0
ac: 08 95 ret
avr-gcc-list at http://avr1.org
- [avr-gcc-list] Optimization problems,
Tvrtko A. Ursulin <=