C union initialization and gcc-15

a contrived example Let’s start from a quiz. What do you think will this program print: #include <stdio.h> __attribute__((noipa)) static void use_stack(void) { volatile int foo[] = { 0x40, 0x41, 0x42, 0x43, }; } __attribute__((noipa)) static int do_it(void) { // use 'volatile' to inhibit constant propagation volatile union { int dummy; struct { int fs[4]; } s; } v = { 0 }; return v.s.fs[3]; } int…