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[missed optimization] Missed removing loop of setting zero when dereference pointer (memset) #139810 
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Description
void f0(unsigned char *ptr, unsigned long len){
for(unsigned long i = 0; i < len; ++i){
ptr[i] = 0;
}
}
void f1(unsigned char *ptr, unsigned long len){
for(unsigned long i = 0; i < len; ++i){
while(ptr[i])
ptr[i]--;
}
}
void f2(unsigned char *ptr){
while(ptr[0])
ptr[0]--;
}
When flags are -O3,
f1() compares if ptr[i] is zero before setting it to zero and f0() memset it to zero.
When flags are -O3 and -march=icelake-client, f1() doesn't call memset like f0().