Andes Workshop

AndeStar has been evolved to V3(the third generation). V3 has more better code size advantage than V2 because we design some new instructons. One example is push25 & pop25, both are 16 bits instructions and can handle prolog and epilog while in V2 compiler has to use 32 bit instruction( smw & lmw) to do the same work.
But push25 hasn't much transformation as smw(it is only 16 bits length), it will store at least 4 GPRs($r6,$gp,$fp,$lp) to stack. For there is a kind of sub function which only needs to save $lp as it doesn't touch other GPR at all. Now compiler in BSP400 has introduced two option "-mno-v3push/-mv3push" to let user to handle this case for different purpose.

First, let's introduce the behavior of BSP400 about the two options:
When optimazation level is "-Os", -mv3push” is implied used, compiler will default use push25 to do prolog. When set "-mno-v3push", compiler will use smw.adw instead.
When optimazation level is other, "-mno-v3push" is implied used, compiler will default use smw.adw to do porlog, when set "-mv3push",compiler will use push25 instead.
For example we can set "-mno-v3push" in AndeSight as:

Compile will use smw instruction as:

other than


Second, with this background, for function which is frequently called and dosen't touch any GPR we can set different optimization level for it to improve performance. The example code is:

__attribute__((optimize("O3")))
int func (… )
{
}

If there are more functions needs to set "-O3", the C code can be as:
#pragma GCC push_options
#pragma GCC optimize ("O3")
int funcA (... )
{
...
}
int funcB (... )
{
...
}
...
#pragma GCC pop_options