https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94387
Bug ID: 94387
Summary: Excess read instructions are generated in case of
writing to fields of volatile + packed type
(structure)
Product: gcc
Version: 9.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: petro.karashchenko at gmail dot com
Target Milestone: ---
Created attachment 48140
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48140&action=edit
preprocessed file
Excess read instructions are generated when access members of volatile + packed
types (structures):
test.c:
----------
#include <stdint.h>
typedef volatile struct type1_s {
uint32_t a1;
uint8_t a2;
uint8_t a3;
uint8_t a4;
uint8_t a5;
} __attribute__((packed)) type1_t;
typedef volatile struct {
uint32_t b1;
uint32_t b2;
} __attribute__((packed)) type2_t;
typedef volatile struct type3_s {
type1_t h1;
volatile union {
uint8_t b[24];
type2_t c1;
} __attribute__((packed)) h2;
} __attribute__((packed)) type3_t;
typedef volatile struct type4_s {
uint32_t x1;
uint8_t x2;
uint16_t x3;
uint8_t x4;
uint8_t x5;
uint8_t x6;
} __attribute__((packed)) type4_t;
static void my_func2(type3_t *p0, type4_t *p1) ;
int my_func1(uint8_t *p0, uint8_t *p1)
{
type3_t *i = (type3_t *)p0;
type4_t *o = (type4_t *)p1;
my_func2(i, o);
return 0;
}
static void my_func2(type3_t *p0, type4_t *p1)
{
p1->x1 = 0xFFFFFF01;
p1->x6 = 1;
p1->x2 = 2;
p1->x4 = p0->h1.a3;
p1->x5 = p0->h1.a4;
p1->x3 = 0;
}
----------
arceb-elf32-gcc -save-temps -Wall -Wextra -c -mcpu=arc600 -mtune=arc600
-mbig-endian -mmul64 test.c -Os
----------
Disassembly:
.global my_func1
.type my_func1, @function
my_func1:
ldb_s r2,[r1]
mov r2,-1 ;6
stb_s r2,[r1]
ldb_s r3,[r1,1]
stb_s r2,[r1,1]
ldb_s r3,[r1,2]
stb_s r2,[r1,2]
ldb_s r2,[r1,3]
mov_s r3,1 ;0
stb_s r3,[r1,3]
stb_s r3,[r1,9]
mov_s r3,2
stb_s r3,[r1,4]
ldb_s r3,[r0,5]
mov_s r2,0 ;0
stb_s r3,[r1,7]
ldb_s r0,[r0,6]
stb_s r0,[r1,8]
ldb_s r0,[r1,5]
stb_s r2,[r1,5]
ldb_s r0,[r1,6]
stb_s r2,[r1,6]
mov_s r0,0 ;0
j_s [blink]
.size my_func1, .-my_func1
----------
Expected disassembly:
.global my_func1
.type my_func1, @function
my_func1:
mov r2,-1 ;6
stb_s r2,[r1]
stb_s r2,[r1,1]
stb_s r2,[r1,2]
mov_s r3,1 ;0
stb_s r3,[r1,3]
stb_s r3,[r1,9]
mov_s r3,2
stb_s r3,[r1,4]
ldb_s r3,[r0,5]
mov_s r2,0 ;0
stb_s r3,[r1,7]
ldb_s r0,[r0,6]
stb_s r0,[r1,8]
stb_s r2,[r1,5]
stb_s r2,[r1,6]
mov_s r0,0 ;0
j_s [blink]
.size my_func1, .-my_func1
----------
I have checked same code compilation with:
arm-none-eabi-gcc -save-temps -Wall -Wextra -c -mcpu=arm7tdmi -mthumb test.c
-Os
The result is pretty much the same, so it is not architecture dependent bug.
