Hi Richard,

As I mentioned in the IRC channel, I managed to get "most" of the 
regression testsuite working for x86_64 (avx512) and aarch64.

On x86_64 I get a failure that I can't explain, was hoping you might be 
able to have a look with me:
"PASS->FAIL: gcc.target/i386/vect-perm-odd-1.c execution test"

vect-perm-odd-1.exe segfaults and when I gdb it seems to be the first 
iteration of the main loop.  The tree dumps look alright, but I do 
notice the stack usage seems to change between --param 
vect-epilogue-nomask={0,1}.

Am I missing to update some field that may later lead to the amount of 
stack being used? I am confused, it could very well be that I am missing 
something obvious, I am not too familiar with x86's ISA. I will try to 
investigate further.

This patch needs further clean-up and more comments (or comment 
updates), but I thought I'd share current state to see if you can help 
me unblock.

Cheers,
Andre