Hughe Stack Usage when having a long Initializer List

[Christoph Rüthing]

Hi,

today I encountered an interesting behavior of GCC for a constructor with a very long initializer list, initializing ~1000 members of different plain types like int, float, ... I see, that GCC stores basically all addresses of the members on the stack and then reads back the addresses one by one to write the initializtion values.

I wonder why GCC behaves like this? For me this is useless stack usage, because it finally have pushed addresses x, x+4, x+8, ...

Note: I am using GCC for ARM version 10.3.1 but we can see the behavior also in newer versions. Check the example here https://godbolt.org/z/qn9xeqvbv and you see that the Test::Test() constructor allocates 940 bytes stack and it stores just increasing addresses on the stack.

Switching to -O1 or -O2 removes this behavior, I think some optimization tries to optimize the code here with the cost of quite big stack usage. Are there options that influence this behavior?

Best Regards,
Christpoh