add sysroot/include/c++/version/${TARGET} to wasm32-wasi

[expnkx]

Summary

The issue is that https://reviews.llvm.org/D117888 does not correctly add include path for libstdc++ which causes compilation to fail.

[tbaeder]

Is the one using MultiarchTriple before wrong? Why is this one being used now even if the OS is unknown?

[sbc100]

In D119056#3299967, @tbaeder wrote:

Is the one using MultiarchTriple before wrong? Why is this one being used now even if the OS is unknown?

Indeed, it looks like this case should already be handled by the // First add the per-target include path if the OS is known. case above. Also, I would expect the MultiarchTriple triple to come before the "/c++/" part of the directory, as it does with the existing path above.

[expnkx]

In D119056#3308981, @sbc100 wrote:

In D119056#3299967, @tbaeder wrote:

Is the one using MultiarchTriple before wrong? Why is this one being used now even if the OS is unknown?

Indeed, it looks like this case should already be handled by the // First add the per-target include path if the OS is known. case above. Also, I would expect the MultiarchTriple triple to come before the "/c++/" part of the directory, as it does with the existing path above.

No.

libstdc++'s <bits/c++config.h> file is stored in the multiarch here.

[expnkx]

Update for upstreaming update

[sbc100]

clang/lib/Driver/ToolChains/WebAssembly.cpp

541

I see, but regardless of if the multi-arch part comes after the c++ or before, shoudln't this patch be changing the first "target specific" path above rather than the second "generic one". i.e. shouldn't we be searching the multi-arch path first and then the generic path second?

[sbc100]

clang/lib/Driver/ToolChains/WebAssembly.cpp

541

I'm a little confused by c++/<version>/<triple> thing... looking at clang/lib/Driver/ToolChains/Fuchsia.cpp and clang/lib/Driver/ToolChains/Gnu.cpp it looks like /<version> is always the last part of the include path. Do you know what the <triple> component would be needed after the version for wasm but not for other platforms?

[expnkx]

I do not know. I have invited Jonathan Wakely. He knows how GCC deals with that and i want to know what he says about this. Then i will fix it later.

[jwakely]

clang/lib/Driver/ToolChains/WebAssembly.cpp

541

Do you know what the <triple> component would be needed after the version for wasm but not for other platforms?

It's always needed. Libstdc++ headers are always split across three directories:

• $prefix/include/c++/$version: Most headers are here, and are target-independent.
• $prefix/include/c++/$version/$triplet: target-specific headers such as bits/c++config.h, CPU-specific atomics (predating __atomic built-ins and libatomic), and headers that depend on the build-time GCC config options like the choice of thread model, locale backend, allocator backend, etc.
• $prefix/include/c++/$version/backward: <strstream> and legacy headers like <hash_map>.

The second one will be modified by the multilib options, so on x86_64 -m32 will use $prefix/include/c++/$version/$triplet/32 instead.

In all cases, $version might be X.Y.Z or just X if GCC was configured with --with-gcc-major-version-only

[tbaeder]

This was fixed via https://reviews.llvm.org/D120251

clang/lib/Driver/ToolChains/WebAssembly.cpp

   }
 
   // Second add the generic one.
-  addSystemInclude(DriverArgs, CC1Args, LibPath + "/c++/" + Version);
+  std::string VersionPath = LibPath + "/c++/" + Version;
+  std::string VersionPathArch = VersionPath;
+  VersionPathArch.push_back('/');
+  VersionPathArch.append(MultiarchTriple);
+  addSystemInclude(DriverArgs, CC1Args, VersionPathArch);
+  addSystemInclude(DriverArgs, CC1Args, VersionPath);
 }