[Driver] Add -print-multiarch

This is useful in runtimes build for example which currently try to
guess the correct triple where to place libraries in the multiarch
layout.  Using this flag, the build system can get the correct triple
directly by querying Clang.

Differential Revision: https://reviews.llvm.org/D101400

Author: petrhosek

clang/include/clang/Driver/Options.td

@@ -3584,6 +3584,8 @@ def print_target_triple : Flag<["-", "--"], "print-target-triple">,
   HelpText<"Print the normalized target triple">;
 def print_effective_triple : Flag<["-", "--"], "print-effective-triple">,
   HelpText<"Print the effective target triple">;
+def print_multiarch : Flag<["-", "--"], "print-multiarch">,
+  HelpText<"Print the multiarch target triple">;
 def print_prog_name_EQ : Joined<["-", "--"], "print-prog-name=">,
   HelpText<"Print the full program path of <name>">, MetaVarName<"<name>">;
 def print_resource_dir : Flag<["-", "--"], "print-resource-dir">,

clang/include/clang/Driver/ToolChain.h

@@ -184,12 +184,6 @@ class ToolChain {
   virtual Tool *buildStaticLibTool() const;
   virtual Tool *getTool(Action::ActionClass AC) const;
 
-  virtual std::string getMultiarchTriple(const Driver &D,
-                                         const llvm::Triple &TargetTriple,
-                                         StringRef SysRoot) const {
-    return TargetTriple.str();
-  }
-
   virtual std::string buildCompilerRTBasename(const llvm::opt::ArgList &Args,
                                               StringRef Component,
                                               FileType Type,
@@ -548,6 +542,12 @@ class ToolChain {
   /// isThreadModelSupported() - Does this target support a thread model?
   virtual bool isThreadModelSupported(const StringRef Model) const;
 
+  virtual std::string getMultiarchTriple(const Driver &D,
+                                         const llvm::Triple &TargetTriple,
+                                         StringRef SysRoot) const {
+    return TargetTriple.str();
+  }
+
   /// ComputeLLVMTriple - Return the LLVM target triple to use, after taking
   /// command line arguments into account.
   virtual std::string

clang/lib/Driver/Driver.cpp

@@ -1900,6 +1900,12 @@ bool Driver::HandleImmediateArgs(const Compilation &C) {
     return false;
   }
 
+  if (C.getArgs().hasArg(options::OPT_print_multiarch)) {
+    llvm::outs() << TC.getMultiarchTriple(*this, TC.getTriple(), SysRoot)
+                 << "\n";
+    return false;
+  }
+
   if (C.getArgs().hasArg(options::OPT_print_targets)) {
     llvm::TargetRegistry::printRegisteredTargetsForVersion(llvm::outs());
     return false;

clang/lib/Driver/ToolChains/Fuchsia.h

@@ -65,6 +65,10 @@ class LLVM_LIBRARY_VISIBILITY Fuchsia : public ToolChain {
     return LangOptions::SSPStrong;
   }
 
+  std::string getMultiarchTriple(const Driver &D,
+                                 const llvm::Triple &TargetTriple,
+                                 StringRef SysRoot) const override;
+
   std::string ComputeEffectiveClangTriple(const llvm::opt::ArgList &Args,
                                           types::ID InputType) const override;
 
@@ -97,10 +101,6 @@ class LLVM_LIBRARY_VISIBILITY Fuchsia : public ToolChain {
 
 protected:
   Tool *buildLinker() const override;
-
-  std::string getMultiarchTriple(const Driver &D,
-                                 const llvm::Triple &TargetTriple,
-                                 StringRef SysRoot) const override;
 };
 
 } // end namespace toolchains

clang/lib/Driver/ToolChains/Linux.h

@@ -23,6 +23,10 @@ class LLVM_LIBRARY_VISIBILITY Linux : public Generic_ELF {
 
   bool HasNativeLLVMSupport() const override;
 
+  std::string getMultiarchTriple(const Driver &D,
+                                 const llvm::Triple &TargetTriple,
+                                 StringRef SysRoot) const override;
+
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
@@ -61,10 +65,6 @@ class LLVM_LIBRARY_VISIBILITY Linux : public Generic_ELF {
   Tool *buildAssembler() const override;
   Tool *buildLinker() const override;
   Tool *buildStaticLibTool() const override;
-
-  std::string getMultiarchTriple(const Driver &D,
-                                 const llvm::Triple &TargetTriple,
-                                 StringRef SysRoot) const override;
 };
 
 } // end namespace toolchains

clang/test/Driver/print-multiarch.c

@@ -0,0 +1,6 @@
+// Check the output of -print-multiarch.
+
+// RUN: %clang -print-multiarch --target=x86_64-unknown-linux-gnu \
+// RUN:        -resource-dir=%S/Inputs/resource_dir \
+// RUN:      | FileCheck --check-prefix=PRINT-MULTIARCH %s
+// PRINT-MULTIARCH: {{^}}x86_64-linux-gnu{{$}}