Hi,

This patch disables epilogue vectorization when we are peeling for 
alignment in the prologue and we can't guarantee the main vectorized 
loop is entered.  This is to prevent executing vectorized code with an 
unaligned access if the target has indicated it wants to peel for 
alignment. We take this conservative approach as we currently do not 
distinguish between peeling for alignment for correctness or for 
performance.

A better codegen would be to make it skip to the scalar epilogue in case 
the main loop isn't entered when alignment peeling is required. However, 
that would require a more aggressive change to the codebase which we 
chose to avoid at this point of development.  We can revisit this option 
during stage 1 if we choose to.

Bootstrapped on aarch64-none-linux and regression tested on 
aarch64-none-elf.

gcc/ChangeLog:

     PR tree-optimization/105219
     * tree-vect-loop.cc (vect_epilogue_when_peeling_for_alignment): New 
function.
     (vect_analyze_loop): Use vect_epilogue_when_peeling_for_alignment 
to determine
     whether to vectorize epilogue.
     * testsuite/gcc.target/aarch64/pr105219.c: New.
     * testsuite/gcc.target/aarch64/pr105219-2.c: New.
     * testsuite/gcc.target/aarch64/pr105219-3.c: New.