Possible bug in xtensa-esp32-elf-g++ (crosstool-NG esp-2021r2-patch5) 8.4.0

[espressif]

Possible bug in xtensa-esp32-elf-g++ (crosstool-NG esp-2021r2-patch5) 8.4.0

[igrr]

@calint I would recommend creating a small reproducer for this issue and uploading it to the Compiler Explorer (godbolt.org). There you can switch between different compilers and architectures and see if this behavior is unique to GCC 8.4 or not.

[calint]

I cannot reproduce it in godbolt. In the actual code it does optimize away a store. I can produce generated assembler with source annotations.

Boiled down to a description in code is:

#include <cstdio>
#include <cstdlib>
#include <iostream>

class object {
   public:
    object **alloc_ptr;
    int x = 1;
    int y = 2;
};

inline __attribute__((always_inline)) object *alloc() {
    object *mem = (object *)malloc(sizeof(object));
    mem->alloc_ptr = (object **)(0xf00ba7); // this store gets optimized away
    return mem;
}

int main() {
    object *o = new (alloc()) object;
    printf("%p\n", o->alloc_ptr); // UB
}

I am probably doing UB... It is solved with the compiler flag.

Thanks