https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70047
--- Comment #2 from Jaak Ristioja <jaak at ristioja dot ee> --- Perhaps the simplest example for x86_64 would be something like: void f(long a1, long a2, long a3, long a4, long a5, long a6, long a7); According to the ABI all seven arguments are classified as INTEGER-s. Arguments a1 through a6 get passed in %rdi, %rsi, %rdx, %rcx, %r8 and %r9 respectively, but a7 will be passed on the stack because no other registers are available. Therefore, in machine code passing/accessing a7 via the stack might be slightly slower than accessing the rest of the variables via registers. The situation gets more complicated with floating-point and aggregate values.
