--- Comment #6 from Chris Hall <gcc at gmch dot uk> ---
Created attachment 43325
Summary of results using Compiler Explorer: for v5.4.0, 6.3.0 and 7.2.0.

Setting -O2 or -O3 on the command line appears to imply -falign-functions=16
and -falign-loops=n, where n is at least 10 but less than 14.

Setting -falign-functions=32 on the command line does the requested alignment,
plus the implied -falign-loops=n for -O2 and -O3 -- except for -Os, which does
no alignment

Setting both -falign-functions=32 and -falign-loops=32 on the command line does
both requested alignments -- except for -Os which does neither and -O0 which
does only the function alignment.

So far, so good.

One might hope that using _Pragma() would have the same effect as the command
line -falign-functions=32 and -falign-loops=32.  Sadly, this is not the case. 
As reported, v7 rejects the pragmas.  But I find that v5.4.0 and v6.3.0, (a)
don't always do the same thing and (b) don't always align loops as requested.

In particular: for -O2 and -O3, setting both align-functions=32 and
align-loops=32 by _Pragma() will: align functions as requested, BUT loops are
aligned to 8 (which is less than useful) !!  

The last set of results looks at compiling with command line -O0 through to -O3
(including -Og and -Os), with _Pragma() for -O3, align-functions=32 and
align-loops=32.  The _Pragma() for -O3 seems to override the command line as
far as this small test is concerned, except for -fomit-frame-pointer.  Sadly,
align-loops=32 is still broken.

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