[clang] [Clang][Docs] Document -Xarch_ better (PR #127890)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Joseph Huber (jhuber6)

<details>
<summary>Changes</summary>

Summary:
This argument is esoteric and previously didn't even work consistently
across the targets. Now that's fixed we should document it better.


---
Full diff: https://github.com/llvm/llvm-project/pull/127890.diff


1 Files Affected:

- (modified) clang/include/clang/Driver/Options.td (+6) 


``````````diff
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 5ad187926e710..b5598a44758a8 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -934,6 +934,12 @@ def Xanalyzer : Separate<["-"], "Xanalyzer">,
   Group<StaticAnalyzer_Group>;
 def Xarch__ : JoinedAndSeparate<["-"], "Xarch_">, Flags<[NoXarchOption]>,
   HelpText<"Pass <arg> to the compiliation if the target matches <arch>">,
+  DocBrief<[{Specifies that the argument should only be used if the compileation
+  target matches the specified architecture. This can be used with the target
+  CPU, triple architecture, or offloading host and device. This is most useful
+  for separating behavior undesirable on one of the targets when combining many
+  compilation jobs, as is commong with offloading. For example, -Xarch_x86_64,
+  -Xarch_gfx90a, and -Xarch_device are all valid selectors.}]>,
   MetaVarName<"<arch> <arg>">;
 def Xarch_host : Separate<["-"], "Xarch_host">, Flags<[NoXarchOption]>,
   HelpText<"Pass <arg> to the CUDA/HIP host compilation">, MetaVarName<"<arg>">;

``````````

</details>


https://github.com/llvm/llvm-project/pull/127890