help removing unnecessary zero-extension

[William Tambe via Gcc-help <gcc-help@xxxxxxxxxxx>]

Given following program:

    unsigned char var;
    int main() {
        return var;
    }

And compiled using:
pu32-elf-gcc -O3 -c -save-temps test.c

Unnecessary zero-extension gets generated after a memory byte load
which already zero-extend.

LOAD_EXTEND_OP has been defined as follow:
#define LOAD_EXTEND_OP(M) ZERO_EXTEND

Find complete port at:
https://github.com/fontamsoc/gcc/commit/45840063
And machine description at:
https://github.com/fontamsoc/gcc/blob/45840063/gcc/config/pu32/pu32.md

Any idea what else can be tried to prevent the unnecessary zero-extension ?