Identified with misc-include-cleaner.

https://github.com/llvm/llvm-project/pull/114550 caused a buildbot breakage (https://lab.llvm.org/buildbot/#/builders/66/builds/5853) because of an unused variable. This patch attempts to fix forward:

/home/b/sanitizer-x86_64-linux/build/llvm-project/llvm/lib/Target/AMDGPU/AMDGPUMachineFunction.cpp:106:24: error: variable 'TTy' set but not used [-Werror,-Wunused-but-set-variable]
106 |     if (TargetExtType *TTy = AMDGPU::isNamedBarrier(GV)) {
    |                        ^

Use a local pointer type to represent the named barrier in builtin and
intrinsic. This makes the definitions more user friendly
bacause they do not need to worry about the hardware ID assignment. Also
this approach is more like the other popular GPU programming language.
Named barriers should be represented as global variables of addrspace(3)
in LLVM-IR. Compiler assigns the special LDS offsets for those variables
during AMDGPULowerModuleLDS pass. Those addresses are converted to hw
barrier ID during instruction selection. The rest of the
instruction-selection changes are primarily due to the
intrinsic-definition changes.

Generated automatically with:
$ clang-tidy -fix -checks=-*,llvm-qualified-auto $(find
lib/Target/AMDGPU/ -type f)

"hidden_dynamic_lds_size" argument will be added in the reserved section
at offset 120 of the implicit argument layout.
Add "isDynamicLDSUsed" flag to AMDGPUMachineFunction to identify if a
function uses dynamic LDS.

hidden argument will be added in below cases:

- LDS global is used in the kernel.
- Kernel calls a function which uses LDS global.
- LDS pointer is passed as argument to kernel itself.

This will represent functions with the amdgpu_cs_chain or
amdgpu_cs_chain_preserve calling conventions.

Differential Revision: https://reviews.llvm.org/D156410

Do the LDS frame calculation once, in the IR pass, instead of repeating the work in the backend.

Prior to this patch:
The IR lowering pass sets up a per-kernel LDS frame and annotates the variables with absolute_symbol
metadata so that the assembler can build lookup tables out of it. There is a fragile association between
kernel functions and named structs which is used to recompute the frame layout in the backend, with
fatal_errors catching inconsistencies in the second calculation.

After this patch:
The IR lowering pass additionally sets a frame size attribute on kernels. The backend uses the same
absolute_symbol metadata that the assembler uses to place objects within that frame size.

Deleted the now dead allocation code from the backend. Left for a later cleanup:
- enabling lowering for anonymous functions
- removing the elide-module-lds attribute (test churn, it's not used by llc any more)
- adjusting the dynamic alignment check to not use symbol names

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D155190

The premise here is to allow non-kernel functions to locate external LDS variables without using LDS or extra magic SGPRs to do so.

1/ First it crawls the callgraph to work out which external LDS variables are reachable from a given kernel
2/ Then it creates a new `extern char[0]` variable for each kernel, which will alias all the other extern LDS variables because that's the documented behaviour of these variables
3/ The address of that variable is written to a lookup table. The global variable is tagged with metadata to track what address it was allocated at by codegen
4/ The assembler builds the lookup table using the metadata
5/ Any non-kernel functions use the same magic intrinsic used by table lookups of non-dynamic LDS variables to find the address to use

Heavy overlap with the code paths taken for other lowering, in particular the same intrinsic is used to pass the dynamic scope information through the same sgpr as for table lookups of static LDS.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D144233