[Bug tree-optimization/89478] New: missed optimization for lambda expression when variable is uninitialized when declared

[SztfG at yandex dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89478

            Bug ID: 89478
           Summary: missed optimization for lambda expression when
                    variable is uninitialized when declared
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: SztfG at yandex dot ru
  Target Milestone: ---

testcase:

constexpr void mul2(int &a, const int b)
{
  a = b * 2;
}

int test = []() {int a; mul2(a, 123); return a;}(); 

int test2 = []() {int a = 0; mul2(a, 123); return a;}();


output for GCC trunk with -O3 -std=c++17
_GLOBAL__sub_I_test:
        movl    $246, test(%rip)
        ret
test2:
        .long   246
test:
        .zero   4


simple testcase:

int test3 = []() {int a; a = 5; return a;}();

_GLOBAL__sub_I_test:
        movl    $5, test(%rip)
        ret
test:
        .zero   4