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Difference in output of llvm-args=--help-list-hidden when llvm.linked-shared is set to true or false #115564

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csmoe opened this issue Sep 5, 2023 · 1 comment · Fixed by #115638
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Difference in output of llvm-args=--help-list-hidden when llvm.linked-shared is set to true or false #115564

csmoe opened this issue Sep 5, 2023 · 1 comment · Fixed by #115638
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C-bug Category: This is a bug.

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@csmoe
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csmoe commented Sep 5, 2023 •
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I noticed a difference in the output of the llvm-args=--help-list-hidden flag when the llvm.link-shared configuration option is set to true or false in config.toml.

Steps to reproduce on Mac:

  1. Set llvm.link-shared=true and llvm.download-ci-llvm=false in the config.toml.
  2. ./x.py build
  3. ./build/<triple>/stage1/bin/rustc -Cllvm-args=--help-list-hidden | rg emit-dwarf-uwind will print the llvm option

Expected behavior:
The output of llvm-args=--help-list-hidden should be consistent regardless of the value of llvm.link-shared. So The emit-dwarf-unwind option should be present in the output regardless of the llvm.link-shared setting.

Actual behavior:
When llvm.link-shared is set to false, the emit-dwarf-unwind option is missing from the output of llvm-args=--help-list-hidden. And llvm was statically linked within rustc on non-Linux platform, while statically linked on Linux; this difference can be seen on Linux and Mac.

Rust Version: latest nightly
@csmoe csmoe added the C-bug Category: This is a bug. label Sep 5, 2023
@rustbot rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Sep 5, 2023
@csmoe
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csmoe commented Sep 5, 2023

btw, --emulated-tls is missing regardless of llvm.link-shared.

@ldm0 ldm0 mentioned this issue Sep 7, 2023
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GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this issue Sep 7, 2023
@GuillaumeGomez
Rollup merge of rust-lang#115638 - ldm0:ldm/llvm-args-fix, r=nikic
060d7dc 
`-Cllvm-args` usability improvement

fixes: rust-lang#26338
fixes: rust-lang#115564

Two problems were found during playing with `-Cllvm-args`

1. When `llvm.link-shared` is set to `false` in `config.toml`, output of `rustc -C llvm-args='--help-list-hidden'` doesn't contain `--emit-dwarf-unwind` and `--emulated-tls`. When it is set to `true`, `rustc -C llvm-args='--help-list-hidden'` emits `--emit-dwarf-unwind`, but `--emulated-tls` is still missing.
2. Setting `-Cllvm-args=--emit-dwarf-unwind=always` doesn't take any effect, but `-Cllvm-args=-machine-outliner-reruns=3` does work.

### 1

Adding `RegisterCodeGenFlags` to register codegen flags fixed the first problem. `rustc -C llvm-args='--help-list-hidden'` emits full codegen flags including `--emit-dwarf-unwind` and `--emulated-tls`.

### 2

Constructing `TargetOptions` from `InitTargetOptionsFromCodeGenFlags` in `LLVMRustCreateTargetMachine` fixed the second problem. The `LLVMRustSetLLVMOptions` calls `ParseCommandLineOptions` which parses given `llvm-args`. For options like `machine-outliner-reruns`, it just works, since the codegen logic directly consumes the parsing result:

[machine-outliner-reruns register](https://github.com/rust-lang/llvm-project/blob/0537f6354cffe546cbf47f6dc9c7f82e49e86cfb/llvm/lib/CodeGen/MachineOutliner.cpp#L114)
[machine-outliner-reruns consumption](https://github.com/rust-lang/llvm-project/blob/0537f6354cffe546cbf47f6dc9c7f82e49e86cfb/llvm/lib/CodeGen/MachineOutliner.cpp#L1138)

But for flags defined in `TargetOptions` and `MCTargetOptions` to take effect, constructing them with `InitTargetOptionsFromCodeGenFlags` is essential, or the parsing result is just not consumed. Similar patterns can be observed in [lli](https://github.com/rust-lang/llvm-project/blob/0537f6354cffe546cbf47f6dc9c7f82e49e86cfb/llvm/tools/llc/llc.cpp#L494), [llc](https://github.com/rust-lang/llvm-project/blob/0537f6354cffe546cbf47f6dc9c7f82e49e86cfb/llvm/tools/lli/lli.cpp#L517), etc.
@bors bors closed this as completed in 575c363 Sep 8, 2023
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Sep 8, 2023
@rust-timer
Unrolled build for rust-lang#115638
78e7f03 
Rollup merge of rust-lang#115638 - ldm0:ldm/llvm-args-fix, r=nikic

`-Cllvm-args` usability improvement

fixes: rust-lang#26338
fixes: rust-lang#115564

Two problems were found during playing with `-Cllvm-args`

1. When `llvm.link-shared` is set to `false` in `config.toml`, output of `rustc -C llvm-args='--help-list-hidden'` doesn't contain `--emit-dwarf-unwind` and `--emulated-tls`. When it is set to `true`, `rustc -C llvm-args='--help-list-hidden'` emits `--emit-dwarf-unwind`, but `--emulated-tls` is still missing.
2. Setting `-Cllvm-args=--emit-dwarf-unwind=always` doesn't take any effect, but `-Cllvm-args=-machine-outliner-reruns=3` does work.

### 1

Adding `RegisterCodeGenFlags` to register codegen flags fixed the first problem. `rustc -C llvm-args='--help-list-hidden'` emits full codegen flags including `--emit-dwarf-unwind` and `--emulated-tls`.

### 2

Constructing `TargetOptions` from `InitTargetOptionsFromCodeGenFlags` in `LLVMRustCreateTargetMachine` fixed the second problem. The `LLVMRustSetLLVMOptions` calls `ParseCommandLineOptions` which parses given `llvm-args`. For options like `machine-outliner-reruns`, it just works, since the codegen logic directly consumes the parsing result:

[machine-outliner-reruns register](https://github.com/rust-lang/llvm-project/blob/0537f6354cffe546cbf47f6dc9c7f82e49e86cfb/llvm/lib/CodeGen/MachineOutliner.cpp#L114)
[machine-outliner-reruns consumption](https://github.com/rust-lang/llvm-project/blob/0537f6354cffe546cbf47f6dc9c7f82e49e86cfb/llvm/lib/CodeGen/MachineOutliner.cpp#L1138)

But for flags defined in `TargetOptions` and `MCTargetOptions` to take effect, constructing them with `InitTargetOptionsFromCodeGenFlags` is essential, or the parsing result is just not consumed. Similar patterns can be observed in [lli](https://github.com/rust-lang/llvm-project/blob/0537f6354cffe546cbf47f6dc9c7f82e49e86cfb/llvm/tools/llc/llc.cpp#L494), [llc](https://github.com/rust-lang/llvm-project/blob/0537f6354cffe546cbf47f6dc9c7f82e49e86cfb/llvm/tools/lli/lli.cpp#L517), etc.
@fmease fmease removed the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Sep 11, 2023
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-Cllvm-args usability improvement ldm0/rust
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