[Bug tree-optimization/100004] New: Dead write not removed when indirection is introduced.

[hiraditya at msn dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100004

            Bug ID: 100004
           Summary: Dead write not removed when indirection is introduced.
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hiraditya at msn dot com
  Target Milestone: ---

struct Foo {
    int x;
};

struct Bar {
    int x;
};

void alias(Foo* foo, Bar* bar) {
    foo->x = 5;
    foo->x = bar->x;
}

struct Wrap1 {
    Foo foo;
};

struct Wrap2 {
    Foo foo;
};

void assign_direct(Wrap1* w1, Wrap2* w2)
{
    w1->foo.x = 5;
    w1->foo.x = w2->foo.x;
}

void assign_via_pointer(Wrap1* w1, Wrap2* w2)
{
    Foo* f1 = &w1->foo;
    Foo* f2 = &w2->foo;
    f1->x = 5;
    f1->x = f2->x;
}


$ gcc-arm64 -O2 -std=c++17 -fstrict-aliasing -S -o -

alias(Foo*, Bar*):
        ldr     w1, [x1]
        str     w1, [x0]
        ret
assign_direct(Wrap1*, Wrap2*):
        ldr     w1, [x1]
        str     w1, [x0]
        ret
assign_via_pointer(Wrap1*, Wrap2*):
        mov     w2, 5
        str     w2, [x0]
        ldr     w1, [x1]
        str     w1, [x0]
        ret