Avoid constructing invalid ConstantRange when Offset + Length in memset
overflows signed 64-bit integer space. This prevents assertion failures
when inferring the initializes attribute.

Fixes #140345

Per LangRef volatile operations can read and write inaccessible memory:

> any volatile operation can read and/or modify state which is not
> accessible via a regular load or store in this module

Model this by adding inaccessible memory effects in getMemoryEffects()
if the operation is volatile.

In the future, we should model volatile using operand bundles instead.

Fixes https://github.com/llvm/llvm-project/issues/120932.

Otherwise the range doesn't make sense since we interpret it as signed.

Fixes #134115

This PR removes the old `nocapture` attribute, replacing it with the new
`captures` attribute introduced in #116990. This change is
intended to be essentially NFC, replacing existing uses of `nocapture`
with `captures(none)` without adding any new analysis capabilities.
Making use of non-`none` values is left for a followup.

Some notes:
* `nocapture` will be upgraded to `captures(none)` by the bitcode
   reader.
* `nocapture` will also be upgraded by the textual IR reader. This is to
   make it easier to use old IR files and somewhat reduce the test churn in
   this PR.
* Helper APIs like `doesNotCapture()` will check for `captures(none)`.
* MLIR import will convert `captures(none)` into an `llvm.nocapture`
   attribute. The representation in the LLVM IR dialect should be updated
   separately.

ConstantRange's constructor asserts that the range not empty, except if
lower/upper are min or max values.

Check if the length is strictly positive instead of just non-negative so
std::nullopt is returned when the size is 0. If that's the case, the
access doesn't initialize anything.

This should fix a crash when building on macOS with ASan & UBsan after
https://github.com/llvm/llvm-project/pull/97373 /
https://github.com/llvm/llvm-project/pull/117104 landed:
https://green.lab.llvm.org/job/llvm.org/job/clang-stage2-cmake-RgSan/664/console

Bail out negative length while inferring initializes attr. Otherwise it
causes an assertion error:
`Attribute 'initializes' does not support unordered ranges`

reland https://github.com/llvm/llvm-project/pull/97373 after fixing
clang tests.

Confirmed with "ninja check-llvm" and "ninja check-clang"

This reverts commit 661c593850715881d2805a59e90e6d87d8b9fbb8.

Multiple buildbot failures, e.g. https://lab.llvm.org/buildbot/#/builders/108/builds/6096

Add the "initializes" attribute inference.

This change is expected to have ~0.09% compile time regression, which
seems acceptable for interprocedural DSE.

https://llvm-compile-time-tracker.com/compare.php?from=9f10252c4ad7cffbbcf692fa9c953698f82ac4f5&to=56345c1cee4375eb5c28b8e7abf4803d20216b3b&stat=instructions%3Au