Prior to this, metadata pertaining to the size or address point offsets
into a relative vtable were twice the value they should be (treating
component widths as pointer width rather than 4 bytes). This prevented
some vtables from being devirtualized with D134320. This ensures the
correct metadata is written so whole program devirtualization can catch
these remaining devirt targets.

Differential Revision: https://reviews.llvm.org/D134687

We don't need to store a full 64-bit immediate. The largest value
used by any opcode is 20 bits.

Using an int32_t shrinks the struct from 16 bytes to 8 bytes and
reduces the size of the SmallVector that we use to store sequences
by 64 bytes.

This is unused in the android toolchain and fixes
https://lab.llvm.org/buildbot/#/builders/77/builds/23883

Reviewed By: Peiming

Differential Revision: https://reviews.llvm.org/D139581

```
/repositories/llvm-project/llvm/include/llvm/Transforms/IPO/Attributor.h:5076:47: note: cast one or both operands to int to silence this warning
1 warning generated.
[ 89% 599/666][ 75% 00:48 + 00:15] Building CXX object lib/Passes/CMakeFiles/LLVMPasses.dir/PassBuilderPipelines.cpp.o
In file included from /repositories/llvm-project/llvm/lib/Passes/PassBuilderPipelines.cpp:42:
/repositories/llvm-project/llvm/include/llvm/Transforms/IPO/Attributor.h:5076:47: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
    bool isWriteOrAssumption() const { return isWrite() | isAssumption(); }
                                              ^~~~~~~~~~~~~~~~~~~~~~~~~~
                                                        ||

```

Fixes https://github.com/llvm/llvm-project/issues/59378

Differential Revision: https://reviews.llvm.org/D139563

Assumptions can help us reason about memory content. This patch teaches
AAPointerInfo to reason about memory assumptions of the following form:

```
%x = load %ptr
... code not writing memory, may include branches ...
%c = %x == %val
... code not writing memory, may include branches ...
llvm.assume(%c)
```

Assumption accesses are recognized from the involved load (%x above).

Assumption accesses are treated special and neither as ordinary read or
write. We use read encoding with an extra flag. Reads are not impacting
other reads or writes. Writes could do that. We don't want assumptions
to impact other writes as they themselves only confirm a value, not
write it. So the "other" write might be required as the assumption only
confirms the effect of that write.