[Driver] Use x86-64 libc++ headers with -m32

[phosek]

Summary

x86 is only used for the bootloader and we use x86-64 libc++ headers
in that case.

[mcgrathr]

lgtm. I'm not sure what better to do that's especially cleaner, except actually just installing i386-fuchsia header subdirs. The easy way to do that would be to just build it all for the target, but we don't have fuchsia libc for that target so it would be a new configuration for bare metal libc++ and we don't actually have anybody who really needs libc++ compiled for that target, only the headers.

[phosek]

After some further discussion, we've decided to generate a __config_site in our build only for the specific purpose.

clang/lib/Driver/ToolChains/Fuchsia.cpp

 }
 
 void Fuchsia::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
                                            ArgStringList &CC1Args) const {
   if (DriverArgs.hasArg(options::OPT_nostdlibinc) ||
       DriverArgs.hasArg(options::OPT_nostdincxx))
     return;
 
-  const Driver &D = getDriver();
-  std::string Target = getTripleString();
+  llvm::Triple Triple = getTriple();
+  // x86 is only used for the bootloader and we use x86-64 headers in that case.
+  if (Triple.getArch() == llvm::Triple::x86)
+    Triple.setArch(llvm::Triple::x86_64);
+
+  switch (GetCXXStdlibType(DriverArgs)) {
+  case ToolChain::CST_Libcxx: {
+    SmallString<128> P(getDriver().Dir);
+    llvm::sys::path::append(P, "..", "include");
 
-  auto AddCXXIncludePath = [&](StringRef Path) {
-    std::string Version = detectLibcxxVersion(Path);
+    std::string Version = detectLibcxxVersion(P);
     if (Version.empty())
       return;
 
-    // First add the per-target include path.
-    SmallString<128> TargetDir(Path);
-    llvm::sys::path::append(TargetDir, Target, "c++", Version);
+    // First add the per-target include path if it exists.
+    SmallString<128> TargetDir(P);
+    llvm::sys::path::append(TargetDir, Triple.str(), "c++", Version);
     if (getVFS().exists(TargetDir))
       addSystemInclude(DriverArgs, CC1Args, TargetDir);
 
     // Second add the generic one.
-    SmallString<128> Dir(Path);
+    SmallString<128> Dir(P);
     llvm::sys::path::append(Dir, "c++", Version);
     addSystemInclude(DriverArgs, CC1Args, Dir);
-  };
-
-  switch (GetCXXStdlibType(DriverArgs)) {
-  case ToolChain::CST_Libcxx: {
-    SmallString<128> P(D.Dir);
-    llvm::sys::path::append(P, "..", "include");
-    AddCXXIncludePath(P);
     break;
   }
 
   default:
     llvm_unreachable("invalid stdlib name");
   }
 }
 

clang/test/Driver/fuchsia.cpp

 // RUN: %clangxx %s -### -no-canonical-prefixes --target=x86_64-unknown-fuchsia \
 // RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     --sysroot=%S/platform -fuse-ld=lld 2>&1 \
 // RUN:     | FileCheck -check-prefixes=CHECK,CHECK-X86_64 %s
 // RUN: %clangxx %s -### -no-canonical-prefixes --target=aarch64-unknown-fuchsia \
 // RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     --sysroot=%S/platform -fuse-ld=lld 2>&1 \
 // RUN:     | FileCheck -check-prefixes=CHECK,CHECK-AARCH64 %s
 // RUN: %clangxx %s -### -no-canonical-prefixes --target=riscv64-unknown-fuchsia \
 // RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     --sysroot=%S/platform -fuse-ld=lld 2>&1 \
 // RUN:     | FileCheck -check-prefixes=CHECK,CHECK-RISCV64 %s
+// RUN: %clangxx %s -### -no-canonical-prefixes --target=x86_64-unknown-fuchsia -m32 \
+// RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
+// RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:     --sysroot=%S/platform -fuse-ld=lld 2>&1 \
+// RUN:     | FileCheck -check-prefixes=CHECK,CHECK-X86_64-M32 %s
 // CHECK: {{.*}}clang{{.*}}" "-cc1"
 // CHECK-X86_64: "-triple" "x86_64-unknown-fuchsia"
 // CHECK-AARCH64: "-triple" "aarch64-unknown-fuchsia"
 // CHECK-RISCV64: "-triple" "riscv64-unknown-fuchsia"
+// CHECK-X86_64-M32: "-triple" "i386-unknown-fuchsia"
 // CHECK-NOT: "-fno-use-init-array"
 // CHECK: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
 // CHECK: "-isysroot" "[[SYSROOT:[^"]+]]"
 // CHECK-X86_64: "-internal-isystem" "{{.*[/\\]}}include{{/|\\\\}}x86_64-unknown-fuchsia{{/|\\\\}}c++{{/|\\\\}}v1"
 // CHECK-AARCH64: "-internal-isystem" "{{.*[/\\]}}include{{/|\\\\}}aarch64-unknown-fuchsia{{/|\\\\}}c++{{/|\\\\}}v1"
 // CHECK-RISCV64: "-internal-isystem" "{{.*[/\\]}}include{{/|\\\\}}riscv64-unknown-fuchsia{{/|\\\\}}c++{{/|\\\\}}v1"
+// CHECK-X86_64-M32: "-internal-isystem" "{{.*[/\\]}}include{{/|\\\\}}x86_64-unknown-fuchsia{{/|\\\\}}c++{{/|\\\\}}v1"
 // CHECK: "-internal-isystem" "{{.*[/\\]}}include{{/|\\\\}}c++{{/|\\\\}}v1"
 // CHECK: "-internal-externc-isystem" "[[SYSROOT]]{{/|\\\\}}include"
 // CHECK: {{.*}}ld.lld{{.*}}" "-z" "now" "-z" "rodynamic" "-z" "separate-loadable-segments"
 // CHECK: "--sysroot=[[SYSROOT]]"
 // CHECK: "-pie"
 // CHECK: "--build-id"
 // CHECK: "-dynamic-linker" "ld.so.1"
 // CHECK: Scrt1.o
 // CHECK-NOT: crti.o
 // CHECK-NOT: crtbegin.o
 // CHECK: "-L[[SYSROOT]]{{/|\\\\}}lib"
 // CHECK: "--push-state"
 // CHECK: "--as-needed"
 // CHECK: "-lc++"
 // CHECK: "-lm"
 // CHECK: "--pop-state"
 // CHECK-X86_64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}x86_64-unknown-fuchsia{{/|\\\\}}libclang_rt.builtins.a"
 // CHECK-AARCH64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}aarch64-unknown-fuchsia{{/|\\\\}}libclang_rt.builtins.a"
 // CHECK-RISCV64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}riscv64-unknown-fuchsia{{/|\\\\}}libclang_rt.builtins.a"
+// CHECK-X86_64-M32: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}i386-unknown-fuchsia{{/|\\\\}}libclang_rt.builtins.a"
 // CHECK: "-lc"
 // CHECK-NOT: crtend.o
 // CHECK-NOT: crtn.o
 
 // RUN: %clangxx %s -### --target=x86_64-unknown-fuchsia -stdlib=libstdc++ \
 // RUN:     -fuse-ld=lld 2>&1 \
 // RUN:     | FileCheck %s -check-prefix=CHECK-STDLIB
 // CHECK-STDLIB: error: invalid library name in argument '-stdlib=libstdc++'