In the Dhrystone benchmark, I find some adjacent global not be merged,
on the contrary the GCC's anchor optimize is work. Use
global-merge-max-offset to set the max offset can yield similar results
(still slightly different, at least we can control the offset).

sorry, this was my mistake

I found that in some performance scenarios, such as under O2, this pr can be helpful for a series of loading global variables.

The llvm.metadata section is not emitted and has special semantics. We
should not merge globals in it, similarly to how we already skip merging
of `llvm.xyz` globals.

Fixes https://github.com/llvm/llvm-project/issues/131394.

For the NewPM, the merge-const option was assigned to an unused
option field. Assign it to the correct one. The merge-const-aggressive
option was not supported -- and invalid options were silently ignored.
Accept it and error on invalid options.

For the LegacyPM, the corresponding cl::opt options were ignored when
called via opt rather than llc.

The module currently stores the target triple as a string. This means
that any code that wants to actually use the triple first has to
instantiate a Triple, which is somewhat expensive. The change in #121652
caused a moderate compile-time regression due to this. While it would be
easy enough to work around, I think that architecturally, it makes more
sense to store the parsed Triple in the module, so that it can always be
directly queried.

For this change, I've opted not to add any magic conversions between
std::string and Triple for backwards-compatibilty purses, and instead
write out needed Triple()s or str()s explicitly. This is because I think
a decent number of them should be changed to work on Triple as well, to
avoid unnecessary conversions back and forth.

The only interesting part in this patch is that the default triple is
Triple("") instead of Triple() to preserve existing behavior. The former
defaults to using the ELF object format instead of unknown object
format. We should fix that as well.

This message was not updated when MinSize was added.

The constructor has an optional bool for the starting value for each
bit. Use that instead of calling set().

Relands #124146 but without changes to the sorting algorithm and the following
reverse.

Reverts llvm/llvm-project#124146 -- new comparator is not a strict-weak
as required by stable_sort.

Co-authored-by: Michael Maitland <michaeltmaitland@gmail.com>