https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88236
Bug ID: 88236
Summary: [avr] Invalid code generated for __memx deference for
avr5 arch
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: saaadhu at gcc dot gnu.org
Target Milestone: ---
Compiling the below code with -mmcu=avr5 -Os (trunk gcc version 9.0.0 20181127
(experimental) (GCC))
void foo (char *a, const __memx char *b)
{
const __memx char *q;
char d;
while (*a++) {
q = b;
do{
d = *q++;
}while(d);
} ;
}
results in incorrect code that looks like this (full code pasted below)
lpm r30,Z
sbrc r23,7
ld r30,Z
Note that the LPM instruction clobbers R30, yet the same reg is used in the
subsequent LD instruction (as part of the Z pointer reg). This is generated for
a __memx char pointer dereference, and will work if the pointee is in program
memory space (sbrc will skip the LD). If the pointee lives in the data address
space though, the LD instruction will execute and yield incorrect results
Generated code:
push r28
/* prologue: function */
/* frame size = 0 */
/* stack size = 1 */
movw r18,r24
.LVL1:
.L2:
movw r30,r18
ld r24,Z
subi r18,-1
sbci r19,-1
.LVL2:
cpse r24,__zero_reg__
rjmp .L4
/* epilogue start */
pop r28
ret
.L4:
movw r24,r20
mov r26,r22
.LVL3:
.L3:
mov r23,r26
mov r30,r24
mov r31,r25
adiw r24,1
adc r26,__zero_reg__
.LVL4:
lpm r30,Z
sbrc r23,7
ld r30,Z
cpse r30,__zero_reg__
rjmp .L3
rjmp .L2
