[Bug c++/81248] New: [AVR] No ipa-sra optimization for small struct / class

[wilhelm.me...@hs-kl.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81248

            Bug ID: 81248
           Summary: [AVR] No ipa-sra optimization for small struct / class
           Product: gcc
           Version: 7.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wilhelm.me...@hs-kl.de
  Target Milestone: ---

In the following minimal example, avr-g++ optimizes the call of f(n1) with
ipa-sra, that is it replaces the pointer-registers with a value-register. The
same should be possible for f(n2), but in this case avr-g++ doesn't make the
same optimization.


#include <cstdint>
#include <type_traits>

struct A {
    A() = default;
    A(const A& o) = default;
    A(const volatile A& o) : m1(o.m1) {} 
    uint8_t m1{0};
};

volatile uint8_t v;

template<typename T>
void f(const T& x) __attribute__((noinline));
template<typename T>
void f(const T& x) {
    if constexpr(std::is_same<std::remove_cv_t<T>, A>::value) {
        v = x.m1;
    }
    else {
        v = x;
    }
}

uint8_t n1;
A n2;

int main() {
    f(n1);
    f(n2);
}