Summary: This pass lowers the `__nvvm_reflect` builtin in the IR. However, this currently runs in the standard optimization pipeline, not just the backend pipeline. This means that if the user creates LLVM-IR without an architecture set, it will always delete the reflect code even if it is intended to be used later. Pushing this into the backend pipeline will ensure that this works as intended, allowing users to conditionally include code depending on which target architecture the user ended up using. This fixes a bug in OpenMP and missing code in `libc`.
Even in cases where handles are supported, references are still preferable for performance. This is because, a ref uses one less register and can avoid the handle creating code associated with taking the address of a tex/surf/sampler.
Identified with misc-include-cleaner.
With this, all machine SSA optimization passes are available in the new codegen pipeline.
Following discussions in #110443, and the following earlier discussions in https://lists.llvm.org/pipermail/llvm-dev/2017-October/117907.html, https://reviews.llvm.org/D38482, https://reviews.llvm.org/D38489, this PR attempts to overhaul the `TargetMachine` and `LLVMTargetMachine` interface classes. More specifically: 1. Makes `TargetMachine` the only class implemented under `TargetMachine.h` in the `Target` library. 2. `TargetMachine` contains target-specific interface functions that relate to IR/CodeGen/MC constructs, whereas before (at least on paper) it was supposed to have only IR/MC constructs. Any Target that doesn't want to use the independent code generator simply does not implement them, and returns either `false` or `nullptr`. 3. Renames `LLVMTargetMachine` to `CodeGenCommonTMImpl`. This renaming aims to make the purpose of `LLVMTargetMachine` clearer. Its interface was moved under the CodeGen library, to further emphasis its usage in Targets that use CodeGen directly. 4. Makes `TargetMachine` the only interface used across LLVM and its projects. With these changes, `CodeGenCommonTMImpl` is simply a set of shared function implementations of `TargetMachine`, and CodeGen users don't need to static cast to `LLVMTargetMachine` every time they need a CodeGen-specific feature of the `TargetMachine`. 5. More importantly, does not change any requirements regarding library linking. cc @arsenm @aeubanks
This change enables constant folding of '`@llvm.nvvm.isspacep.*`' intrinsics if the address space can be propagated in InferAdressSpace.
byval arguments in NVPTX are special. We're only allowed to read from them using a special instruction, and if we ever need to write to them or take an address, we must make a local copy and use it, instead. The problem is that local copies are very expensive, and we create them very late in the compilation pipeline, so LLVM does not have much of a chance to eliminate them, if they turn out to be unnecessary. One way around that is to create such copies early on, and let them percolate through the optimizations. The copying itself will never trigger creation of another copy later on, as the reads are allowed. If LLVM can eliminate it, it's a win. It the full optimization pipeline can't remove the copy, that's as good as it gets in terms of the effort we could've done, and it's certainly a much better effort than what we do now. This early injection of the copies has potential to create undesireable side-effects, so it's disabled by default, for now, until it sees more testing.