Now that #149310 has restricted lifetime intrinsics to only work on
allocas, we can also drop the explicit size argument. Instead, the size
is implied by the alloca.

This removes the ability to only mark a prefix of an alloca alive/dead.
We never used that capability, so we should remove the need to handle
that possibility everywhere (though many key places, including stack
coloring, did not actually respect this).

Split out from #150248:

Since #150944 the size passed to lifetime.start/end is considered
meaningless. The lifetime always applies to the whole alloca.

Accordingly remove handling for size mismatch in the StackLifetime
analysis.

This slightly relaxes the invariant established in #149310, by also
allowing the lifetime argument to be poison. This is to support the
typical pattern of RAUWing with poison when removing an instruction.

It's worth noting that this does not require any conservative
assumptions, lifetimes with poison arguments can simply be skipped.

Fixes https://github.com/llvm/llvm-project/issues/151119.

After #149310 the pointer argument of lifetime.start/lifetime.end is
guaranteed to be an alloca, so we don't need to go through
findAllocaForValue() anymore, and don't have to have special handling
for the case where it fails.

Similar to https://github.com/llvm/llvm-project/pull/96902, this adds
`getDataLayout()` helpers to Function and GlobalValue, replacing the
current `getParent()->getDataLayout()` pattern.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D144365

When fetching allocation sizes, we almost always want to have the
size in bytes, but we were only providing an InBits API. Also add
the corresponding byte-based conjugate to save some *8 and /8
juggling everywhere.

CFG with cycles may requires additional passes of "while (Changed)"
iteration if to propagate data back from latter blocks to earlier blocks,
ordered according to depth_fist.

OR logic, used for ::May, converge to stable state faster then AND logic
use for ::Must.

Though the better solution is to switch to some some form of queue, but
having that this one is good enough, I will consider to do that later.

We can switch ::Must to OR logic if we calculate "may be dead" instead
of direct "must be alive" and then convert values to match existing
interface.

Additionally it fixes correctness in "@cycle" test.

Reviewed By: kstoimenov, fmayer

Differential Revision: https://reviews.llvm.org/D134796