http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53085
--- Comment #1 from brag <unixoid2003 at mail dot ru> 2012-04-23 12:58:17 UTC
---
struct aa{
volatile unsigned short a;
unsigned short b;
volatile unsigned short c;
unsigned short d;
};
#define AAmem ((struct aa *) 256)
static inline unsigned int tx(unsigned int v){
while(AAmem->a&1);
AAmem->c=v;
while(AAmem->a&2);
v=AAmem->c;
return v;
}
void f(){
tx(0xff);
tx(0xff);
}
Compiled by:
arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -O2 -fomit-frame-pointer
-ffreestanding -fno-common -Wall -Wextra -x c -c test.cpp
OR
arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -O2 -fomit-frame-pointer
-ffreestanding -fno-common -Wall -Wextra -x c++ -c test.cpp
The code generated is wrong. There should be two writes to AAmem->c bute there
is one write (strh r3, [r2, #4])
arm-none-eabi-objdump -d test.o :
test.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <f>:
0: f44f 7180 mov.w r1, #256 ; 0x100
4: 880b ldrh r3, [r1, #0]
6: f44f 7280 mov.w r2, #256 ; 0x100
a: 07d8 lsls r0, r3, #31
c: d4fa bmi.n 4 <f+0x4>
e: 23ff movs r3, #255 ; 0xff
10: 8093 strh r3, [r2, #4]
12: 4611 mov r1, r2
14: 880b ldrh r3, [r1, #0]
16: f44f 7280 mov.w r2, #256 ; 0x100
1a: f003 0302 and.w r3, r3, #2
1e: b29b uxth r3, r3
20: 2b00 cmp r3, #0
22: d1f7 bne.n 14 <f+0x14>
24: 8893 ldrh r3, [r2, #4]
26: 8813 ldrh r3, [r2, #0]
28: 07db lsls r3, r3, #31
2a: d4fc bmi.n 26 <f+0x26>
2c: f44f 7280 mov.w r2, #256 ; 0x100
30: 8813 ldrh r3, [r2, #0]
32: f003 0302 and.w r3, r3, #2
36: b29b uxth r3, r3
38: 2b00 cmp r3, #0
3a: d1f9 bne.n 30 <f+0x30>
3c: f44f 7380 mov.w r3, #256 ; 0x100
40: 889b ldrh r3, [r3, #4]
42: 4770 bx lr
