[PATCH] D146973: [Clang] Implicitly include LLVM libc headers for the GPU

[Joseph Huber via Phabricator via cfe-commits]

jhuber6 added inline comments.


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Comment at: clang/lib/Driver/ToolChains/Clang.cpp:1230
+      llvm::sys::path::append(P, "llvm-libc");
+      CmdArgs.push_back("-c-isystem");
+      CmdArgs.push_back(Args.MakeArgString(P));
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tra wrote:
> Ensuring the right include order will be tricky. Interaction between the headers provided by llvm-libc vs the system headers will be interesting if we end up mixing the headers. It may be less problematic compared to the C++ standard library, but I doubt that mixing two implementations would work well here, either. 
> 
> So, the major question I have -- does adding include path here guarantees that we're not picking up the host headers? I do not see any changes that would exclude system headers from include paths.
> If we do have include paths leading to both llvm-libc and the host headers, what's expected to happen if user code ends up including a header that's not present in  llvm-libc? Is that possible?
> 
Right now I'm just kind of relying on an expectation that since this will be the first `c-isystem` path set, then it will pull in these libraries first if they exist. It's not captured by the tests, but compiling with `-v` shows this path being used first in my experience. So, theoretically, if there is an implementation of said header in this location, it will be picked up before anything else. Otherwise it'll just search the other standard locations.


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Comment at: clang/test/Driver/gpu-libc-headers.c:14
+// RUN:     FileCheck %s --check-prefix=CHECK-HEADERS
+// CHECK-HEADERS: "-cc1"{{.*}}"-c-isystem" "{{.*}}include/llvm-libc"
+
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tra wrote:
> I think here we want to test for not just the presence of `include/llvm-libc`, but also that it's in the correct position relative to other include paths. 
> 
> We may want something similar to what we have in clang/test/Driver/hip-include-path.hip
Yeah, I wasn't sure if there was a good way to guarantee a certain path since those can change based on the system. Maybe `--sysroot`?


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  https://reviews.llvm.org/D146973/new/

https://reviews.llvm.org/D146973