-fipa-struct-reorg

This option optimizes the memory space layout. That is, the structure members in the memory are rearranged to improve the cache hit ratio.

Split the cold and hot members in the structure into two structure types.
Figure 1 Structure splitting optimization principle

Change the following structure:

struct S
{
    type1 field1; // Hot field
    type2 field2;
};
S *v;

To:

struct S_hot
{
    type1 field1;
};
struct S_cold 
{
    type2 field2;
};
S_hot *v_hot;S_cold *v_cold;

Optimize the structure array. Convert the array with elements of the structure type into the structure with array members.

Figure 2 Structure array optimization principle

Change the following structure:

struct 
{
    type1 field1;
    type2 field2;
    type3 field3;
} arr[N];

To:

struct
{
    type1 field1[N];
    type2 field2[N];
    type3 field3[N];
} arr;

Add the following content to the option:

-O3 -flto -flto-partition=one -fipa-struct-reorg

The -fipa-struct-reorg option can be enabled only when -O3 -flto -flto-partition=one is enabled at the same time.

Optimization effect: Up to 20% performance improvement is observed on the SPEC CPU 2017 intrate 505.mcf benchmark.

Parent topic: Static Compilation Optimization