memory accesses

[Adi]

Hi,

I am writing a code which mimicks the memory accesses of an
application. Lets assume that array a[] contains all the addresses
accessed in sequence, check the for loop in the code given below. Now,
i want to mimick these accesses(not absolutely but atleast
relatively). I could see only one solution to that - writing a for
loop(see the code). But it gives extra memory accesses, accesing
address of index i and a along with the to b mimicked accesses.

main()
{
int a[300]; //stores the addresses
char x[5000]; //character array to mimick the memory accesses
int i;

a[0] = 0;
for(i=1;i<300;i++)
a = a[i-1]+16; //storing the addresses in the
array

x[0] = 0;
for(i=1;i<300;i++)
{
x[a]='0'; //mimick the realtive memory
accesses.
}
}

Is there any other solution to bypass these unwanted accesses like
storing value of i in registers etc... ?

Thanks.

 

[Mike Wahler]

Hi,

I am writing a code which mimicks the memory accesses of an
application. Lets assume that array a[] contains all the addresses
accessed in sequence, check the for loop in the code given below. Now,
i want to mimick these accesses(not absolutely but atleast
relatively). I could see only one solution to that - writing a for
loop(see the code). But it gives extra memory accesses, accesing
address of index i and a along with the to b mimicked accesses.

main()
{
int a[300]; //stores the addresses
char x[5000]; //character array to mimick the memory accesses
int i;

a[0] = 0;
for(i=1;i<300;i++)
a = a[i-1]+16; //storing the addresses in the
array

x[0] = 0;
for(i=1;i<300;i++)
{
x[a]='0'; //mimick the realtive memory
accesses.
}
}

Is there any other solution to bypass these unwanted accesses like
storing value of i in registers etc... ?

How do you know that 'i' isn't already being stored in a register?

Profile your code before trying to second-guess your compiler.

-Mike

 

[Adi]

main()
{
int a[300]; //stores the addresses
char x[5000]; //character array to mimick the memory accesses
int i;

a[0] = 0;
for(i=1;i<300;i++)
a = a[i-1]+16; //storing the addresses in the
array

x[0] = 0;
for(i=1;i<300;i++)
{
x[a]='0'; //mimick the realtive memory
accesses.
}
}

Is there any other solution to bypass these unwanted accesses like
storing value of i in registers etc... ?

How do you know that 'i' isn't already being stored in a register?

Profile your code before trying to second-guess your compiler.

I have profiled the code and i see 4 memory accesses(3 for i and 1 for
array a)between each access for x.

 

[Mike Wahler]

main()
{
int a[300]; //stores the addresses
char x[5000]; //character array to mimick the memory accesses
int i;

a[0] = 0;
for(i=1;i<300;i++)
a = a[i-1]+16; //storing the addresses in the
array

x[0] = 0;
for(i=1;i<300;i++)
{
x[a]='0'; //mimick the realtive memory
accesses.
}
}

Is there any other solution to bypass these unwanted accesses like
storing value of i in registers etc... ?

How do you know that 'i' isn't already being stored in a register?

Profile your code before trying to second-guess your compiler.

I have profiled the code and i see 4 memory accesses(3 for i and 1 for
array a)between each access for x.

And have you researched all the optimization switches of
your implementation? Have you proven that your code's
performance is somehow unacceptable? If so, perhaps you
need to drop down a level, and do this part with assembly
language, where you *can* have such low-level control.

-Mike