[Driver] Detect libstdc++ include paths for native gcc (-m32 and -m64) on Debian i386

[MaskRay]

Summary

Take gcc-8 on Debian i386 as an example. The target-specific libstdc++ search
path (GPLUSPLUS_TOOL_INCLUDE_DIR) uses the multiarch name i386-linux-gnu,
instead of the triple of the GCC installation i686-linux-gnu (the directory
under usr/lib/gcc/):

/usr/include/c++/8
/usr/include/i386-linux-gnu/c++/8
/usr/include/c++/8/backward

Clang currently detects /usr/lib/gcc/i686-linux-gnu/8/../../../include/i686-linux-gnu/c++/8.
This patch changes the second i686-linux-gnu to i386-linux-gnu so that
/usr/include/i386-linux-gnu/c++/8 can be found.

Fix PR49827 - this was somehow regressed by my previous libstdc++ include path
cleanups and fixes for gcc-cross, but it seems that the paths were never properly tested before.

[MaskRay]

git add two .keep files

[MaskRay]

From an upstream multiarch build of gcc, the libstdc++ search paths are

/tmp/opt/gcc-debug/lib/gcc/x86_64-pc-linux-gnu/11.0.1/../../../../include/c++/11.0.1
/tmp/opt/gcc-debug/lib/gcc/x86_64-pc-linux-gnu/11.0.1/../../../../include/c++/11.0.1/x86_64-pc-linux-gnu
/tmp/opt/gcc-debug/lib/gcc/x86_64-pc-linux-gnu/11.0.1/../../../../include/c++/11.0.1/backward

(this is similar to cross gcc on Debian, except that cross gcc usually uses ../../../../$triple/include/c++/$v)

If you specify --target=x86_64-linux-gnu and install it to /usr, the paths will become.

/usr/include/c++/11.0.1
/usr/include/c++/11.0.1/x86_64-linux-gnu  # for i686-linux-gnu this should be /usr/include/c++/11.0.1/i686-linux-gnu (i686 instead of i386)
/usr/include/c++/11.0.1/backward

If Debian can drop the incdir patch for native gcc, it can reduce some maintenance burden and clang driver can still detect the libstdc++ search paths

[sylvestre.ledru]

Many thanks. it fixed my issues!

/usr/include/i386-linux-gnu/c++/8 is indeed much nicer :)

Thanks for all your hard work on fixing the header detection. it was indeed too complex!

And, thanks for asking for review ;)

About the g++-multiarch-incdir.diff, I cced the gcc maintainer!

clang/lib/Driver/ToolChains/Gnu.cpp

Generic_GCC::addGCCLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
   const GCCVersion &Version = GCCInstallation.getVersion();
 
   // Try /../$triple/include/c++/$version then /../include/c++/$version.
   if (addLibStdCXXIncludePaths(
           LibDir.str() + "/../" + TripleStr + "/include/c++/" + Version.Text,
           TripleStr, Multilib.includeSuffix(), DriverArgs, CC1Args))
     return true;
   // Detect Debian g++-multiarch-incdir.diff.
+  StringRef DebianMultiarch =
+      GCCInstallation.getTriple().getArch() == llvm::Triple::x86
+          ? "i386-linux-gnu"
+          : TripleStr;
   if (addLibStdCXXIncludePaths(LibDir.str() + "/../include/c++/" + Version.Text,
-                               TripleStr, Multilib.includeSuffix(), DriverArgs,
-                               CC1Args, /*Debian=*/true))
+                               DebianMultiarch, Multilib.includeSuffix(),
+                               DriverArgs, CC1Args, /*Debian=*/true))
     return true;
 
   // Otherwise, fall back on a bunch of options which don't use multiarch
   // layouts for simplicity.
   const std::string LibStdCXXIncludePathCandidates[] = {
       // Gentoo is weird and places its headers inside the GCC install,
       // so if the first attempt to find the headers fails, try these patterns.
       InstallDir.str() + "/include/g++-v" + Version.Text,

clang/test/Driver/linux-cross.cpp

 // DEBIAN_X86_64_M32-SAME: {{^}} "-L[[SYSROOT]]/usr/lib/gcc/x86_64-linux-gnu/10/../../../../lib32"
 // DEBIAN_X86_64_M32-SAME: {{^}} "-L[[SYSROOT]]/lib/i386-linux-gnu"
 // DEBIAN_X86_64_M32-SAME: {{^}} "-L[[SYSROOT]]/lib/../lib32"
 // DEBIAN_X86_64_M32-SAME: {{^}} "-L[[SYSROOT]]/usr/lib/i386-linux-gnu"
 // DEBIAN_X86_64_M32-SAME: {{^}} "-L[[SYSROOT]]/usr/lib/../lib32"
 // DEBIAN_X86_64_M32-SAME: {{^}} "-L[[SYSROOT]]/lib"
 // DEBIAN_X86_64_M32-SAME: {{^}} "-L[[SYSROOT]]/usr/lib"
 
+/// Test native GCC installation on Debian i386.
+// RUN: %clang -### %s --target=i686-linux-gnu --sysroot=%S/Inputs/debian_i386_tree \
+// RUN:   -resource-dir=%S/Inputs/resource_dir --stdlib=platform --rtlib=platform 2>&1 | FileCheck %s --check-prefix=DEBIAN_I686
+// DEBIAN_I686:      "-resource-dir" "[[RESOURCE:[^"]+]]"
+// DEBIAN_I686:      "-internal-isystem"
+// DEBIAN_I686-SAME: {{^}} "[[SYSROOT:[^"]+]]/usr/lib/gcc/i686-linux-gnu/10/../../../../include/c++/10"
+/// Debian specific - the path component after 'include' is i386-linux-gnu even
+/// though the installation is i686-linux-gnu.
+// DEBIAN_I686-SAME: {{^}} "-internal-isystem" "[[SYSROOT:[^"]+]]/usr/lib/gcc/i686-linux-gnu/10/../../../../include/i386-linux-gnu/c++/10"
+// DEBIAN_I686-SAME: {{^}} "-internal-isystem" "[[SYSROOT:[^"]+]]/usr/lib/gcc/i686-linux-gnu/10/../../../../include/c++/10/backward"
+// DEBIAN_I686-SAME: {{^}} "-internal-isystem" "[[RESOURCE]]/include"
+// DEBIAN_I686-SAME: {{^}} "-internal-isystem" "[[SYSROOT]]/usr/local/include"
+/// This resolves to /usr/i686-linux-gnu/include. Because it does not exist,
+/// having it does no harm albeit not ideal.
+// DEBIAN_I686-SAME: {{^}} "-internal-isystem" "[[SYSROOT:[^"]+]]/usr/lib/gcc/i686-linux-gnu/10/../../../../i686-linux-gnu/include"
+// DEBIAN_I686:      "-internal-externc-isystem"
+// DEBIAN_I686-SAME: {{^}} "[[SYSROOT]]/usr/include/i386-linux-gnu"
+// DEBIAN_I686:      "-L
+// DEBIAN_I686-SAME: {{^}}[[SYSROOT]]/usr/lib/gcc/i686-linux-gnu/10"
+// DEBIAN_I686-SAME: {{^}} "-L[[SYSROOT]]/lib/i386-linux-gnu"
+// DEBIAN_I686-SAME: {{^}} "-L[[SYSROOT]]/usr/lib/i386-linux-gnu"
+// DEBIAN_I686-SAME: {{^}} "-L[[SYSROOT]]/lib"
+// DEBIAN_I686-SAME: {{^}} "-L[[SYSROOT]]/usr/lib"
+
+/// Test -m64 on Debian i386.
+// RUN: %clang -### %s --target=i686-linux-gnu --sysroot=%S/Inputs/debian_i386_tree -m64 \
+// RUN:   -resource-dir=%S/Inputs/resource_dir --stdlib=platform --rtlib=platform 2>&1 | FileCheck %s --check-prefix=DEBIAN_I686_M64
+// DEBIAN_I686_M64:      "-resource-dir" "[[RESOURCE:[^"]+]]"
+// DEBIAN_I686_M64:      "-internal-isystem"
+// DEBIAN_I686_M64-SAME: {{^}} "[[SYSROOT:[^"]+]]/usr/lib/gcc/i686-linux-gnu/10/../../../../include/c++/10"
+/// Debian specific - the path component after 'include' is i386-linux-gnu even
+/// though the installation is i686-linux-gnu.
+// DEBIAN_I686_M64-SAME: {{^}} "-internal-isystem" "[[SYSROOT:[^"]+]]/usr/lib/gcc/i686-linux-gnu/10/../../../../include/i386-linux-gnu/c++/10/64"
+// DEBIAN_I686_M64-SAME: {{^}} "-internal-isystem" "[[SYSROOT:[^"]+]]/usr/lib/gcc/i686-linux-gnu/10/../../../../include/c++/10/backward"
+// DEBIAN_I686_M64-SAME: {{^}} "-internal-isystem" "[[RESOURCE]]/include"
+// DEBIAN_I686_M64-SAME: {{^}} "-internal-isystem" "[[SYSROOT]]/usr/local/include"
+// DEBIAN_I686_M64-SAME: {{^}} "-internal-isystem" "[[SYSROOT:[^"]+]]/usr/lib/gcc/i686-linux-gnu/10/../../../../i686-linux-gnu/include"
+// DEBIAN_I686_M64:      "-internal-externc-isystem"
+// DEBIAN_I686_M64-SAME: {{^}} "[[SYSROOT]]/usr/include/x86_64-linux-gnu"
+// DEBIAN_I686_M64:      "-L
+// DEBIAN_I686_M64-SAME: {{^}}[[SYSROOT]]/usr/lib/gcc/i686-linux-gnu/10/64"
+// DEBIAN_I686_M64-SAME: {{^}} "-L[[SYSROOT]]/usr/lib/gcc/i686-linux-gnu/10/../../../../lib64"
+// DEBIAN_I686_M64-SAME: {{^}} "-L[[SYSROOT]]/lib/x86_64-linux-gnu"
+// DEBIAN_I686_M64-SAME: {{^}} "-L[[SYSROOT]]/lib/../lib64"
+// DEBIAN_I686_M64-SAME: {{^}} "-L[[SYSROOT]]/usr/lib/x86_64-linux-gnu"
+// DEBIAN_I686_M64-SAME: {{^}} "-L[[SYSROOT]]/usr/lib/../lib64"
+// DEBIAN_I686_M64-SAME: {{^}} "-L[[SYSROOT]]/lib"
+// DEBIAN_I686_M64-SAME: {{^}} "-L[[SYSROOT]]/usr/lib"
+
 /// Test a cross compiler.
 // RUN: %clang -### %s --target=aarch64-linux-gnu --sysroot=%S/Inputs/debian_multiarch_tree \
 // RUN:   -resource-dir=%S/Inputs/resource_dir --stdlib=platform --rtlib=platform 2>&1 | FileCheck %s --check-prefix=DEBIAN_AARCH64
 // DEBIAN_AARCH64:      "-resource-dir" "[[RESOURCE:[^"]+]]"
 // DEBIAN_AARCH64:      "-internal-isystem"
 // DEBIAN_AARCH64-SAME: {{^}} "[[SYSROOT:[^"]+]]/usr/lib/gcc-cross/aarch64-linux-gnu/10/../../../../aarch64-linux-gnu/include/c++/10"
 // DEBIAN_AARCH64-SAME: {{^}} "-internal-isystem" "[[SYSROOT:[^"]+]]/usr/lib/gcc-cross/aarch64-linux-gnu/10/../../../../aarch64-linux-gnu/include/c++/10/aarch64-linux-gnu"
 // DEBIAN_AARCH64-SAME: {{^}} "-internal-isystem" "[[SYSROOT:[^"]+]]/usr/lib/gcc-cross/aarch64-linux-gnu/10/../../../../aarch64-linux-gnu/include/c++/10/backward"