The gcov version is set to 11.1 (compatible with gcov 9) even if
`-Xclang -coverage-version=` specified version is less than 11.1.

Therefore, we can drop producer support for version < 11.1.

This PR registers the writeout and reset functions for `gcov` for all
modules in the PGO runtime, instead of registering them
using global constructors in each module. The change is made for AIX
only, but the same mechanism works on Linux on Power.

When registering such functions using global constructors in each module
without `-ffunction-sections`, the AIX linker cannot garbage collect
unused undefined symbols, because such symbols are grouped in the same
section as the `__sinit` symbol. Keeping such undefined symbols causes
link errors (see test case
https://github.com/llvm/llvm-project/pull/108570/files#diff-500a7e1ba871e1b6b61b523700d5e30987900002add306e1b5e4972cf6d5a4f1R1
for this scenario). This PR implements the initialization in the
runtime, hence avoiding introducing `__sinit` into each module.

The implementation adds a new global variable `__llvm_covinit_functions`
to each module. This new global variable contains the function pointers
to the `Writeout` and `Reset` functions. `__llvm_covinit_functions`'s
section is the named section `__llvm_covinit`. The linker will aggregate
all the `__llvm_covinit` sections from each module
to form one single named section in the final binary. The pair of
functions
```
const __llvm_gcov_init_func_struct *__llvm_profile_begin_covinit();
const __llvm_gcov_init_func_struct *__llvm_profile_end_covinit();
```
are implemented to return the start and end address of this named
section in the final binary, and they are used in function
```
__llvm_profile_gcov_initialize()
```
(which is a constructor function in the runtime) so the runtime knows
the addresses of all the `Writeout` and `Reset` functions from all the
modules.

One noticeable implementation detail relevant to AIX is that to preserve
the `__llvm_covinit` from the linker's garbage collection, a `.ref`
pseudo instruction is inserted into them, referring to the section that
contains the `__llvm_gcov_ctr` variables, which are used in the
instrumented code. The `__llvm_gcov_ctr` variables did not belong to
named sections before, but this PR added them to the
`__llvm_gcov_ctr_section` named section, so we can add a `.ref` pseudo
instruction that refers to them in the `__llvm_covinit` section.

This helps check clang generated good IR in the first place, as
otherwise this can cause UB in subsequent passes, with the final
verification pass not catching any issues.

This for example would have helped catch
https://github.com/llvm/llvm-project/issues/67937 earlier.

-coverage-notes-file=aaa.gcno -coverage-data-file=bbb.gcda creates aaa.gcno in
the current directory (a pattern to be avoided; which may be read-only in an
alternative lit runner).

After a07b135ce0c0111bd83450b5dc29ef0381cdbc39, we always pass
-coverage-notes-file/-coverage-data-file for driver options
-ftest-coverage/-fprofile-arcs/--coverage. As a bonus, we can make the following
simplification to cc1 options:

* `-ftest-coverage -coverage-notes-file a.gcno` => `-coverage-notes-file a.gcno`
* `-fprofile-arcs -coverage-data-file a.gcda` => `-coverage-data-file a.gcda`

and remove EmitCovNotes/EmitCovArcs.

This seems to cause large regressions in existing code, as much as 75% slower
(4x the time taken). Small always inline functions seem to be used a lot in the
cmsis-dsp library.

I would add a phase ordering test to show the problems, but one already exists!
The llvm/test/Transforms/PhaseOrdering/ARM/arm_mult_q15.ll was just changed by
removing alwaysinline to hide the problems that existed.

This reverts commit cae033dcf227aeecf58fca5af6fc7fde1fd2fb4f.
This reverts commit 8e33c41e72ad42e4c27f8cbc3ad2e02b169637a1.

We have several situations where it's beneficial for code size to ensure that every
call to always-inline functions are inlined before normal inlining decisions are
made. While the normal inliner runs in a "MandatoryOnly" mode to try to do this,
it only does it on a per-SCC basis, rather than the whole module. Ensuring that
all mandatory inlinings are done before any heuristic based decisions are made
just makes sense.

Despite being referred to the "legacy" AlwaysInliner pass, it's already necessary
for -O0 because the CGSCC inliner is too expensive in compile time to run at -O0.

This also fixes an exponential compile time blow up in
https://github.com/llvm/llvm-project/issues/59126

Differential Revision: https://reviews.llvm.org/D143624

This has been the default for a while and we're in the process of removing the legacy PM optimization pipeline.

This patch adds a new pass to add !annotation metadata for entries in
@llvm.global.anotations, which is generated  using
__attribute__((annotate("_name"))) on functions in Clang.

This has been discussed on llvm-dev as part of
    RFC: Combining Annotation Metadata and Remarks
    http://lists.llvm.org/pipermail/llvm-dev/2020-November/146393.html

Reviewed By: thegameg

Differential Revision: https://reviews.llvm.org/D91195