[clang] [CUDA][HIP] improve error message for missing cmath (PR #122155)

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llvmbot wrote:


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@llvm/pr-subscribers-backend-x86

@llvm/pr-subscribers-clang

Author: Yaxun (Sam) Liu (yxsamliu)

<details>
<summary>Changes</summary>

One common error seen in CUDA/HIP compilation is:

fatal error: 'cmath' file not found

which is due to inproper installation of standard C++ libraries.

Since it happens with #include_next, users may feel confusing which cmath is not found and how to fix it.

Add an error directive to help users resolve this issue.

---
Full diff: https://github.com/llvm/llvm-project/pull/122155.diff


1 Files Affected:

- (modified) clang/lib/Headers/cuda_wrappers/cmath (+4) 


``````````diff
diff --git a/clang/lib/Headers/cuda_wrappers/cmath b/clang/lib/Headers/cuda_wrappers/cmath
index 45f89beec9b4df..7deca678bf252e 100644
--- a/clang/lib/Headers/cuda_wrappers/cmath
+++ b/clang/lib/Headers/cuda_wrappers/cmath
@@ -24,7 +24,11 @@
 #ifndef __CLANG_CUDA_WRAPPERS_CMATH
 #define __CLANG_CUDA_WRAPPERS_CMATH
 
+#if __has_include_next(<cmath>)
 #include_next <cmath>
+#else
+#error "Could not find standard C++ header 'cmath'. Add -v to your compilation command to check the include paths being searched. You may need to install the appropriate standard C++ library package corresponding to the search path."
+#endif
 
 #if defined(_LIBCPP_STD_VER)
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/122155