[Driver] Enable Classic Flang cross-compilation, e.g. from X86 to AArch64

Co-authored-by: Prabhdeep Singh Soni <[email protected]>

Author: bryanpkc

clang/lib/Driver/ToolChains/ClassicFlang.cpp

@@ -668,7 +668,11 @@ void ClassicFlang::ConstructJob(Compilation &C, const JobAction &JA,
   /***** Upper part of the Fortran frontend *****/
 
   // TODO do we need to invoke this under GDB sometimes?
-  const char *UpperExec = Args.MakeArgString(getToolChain().GetProgramPath("flang1"));
+  std::string flang1 = "flang1";
+  if (getToolChain().isCrossCompiling())
+    flang1 = getToolChain().getEffectiveTriple().getTriple() + "-" + flang1;
+  const char *UpperExec =
+      Args.MakeArgString(getToolChain().GetProgramPath(flang1.c_str()));
 
   UpperCmdArgs.push_back("-opt"); UpperCmdArgs.push_back(Args.MakeArgString(OptOStr));
   UpperCmdArgs.push_back("-terse"); UpperCmdArgs.push_back("1");
@@ -998,8 +1002,11 @@ void ClassicFlang::ConstructJob(Compilation &C, const JobAction &JA,
       Args.hasArg(options::OPT_E)) return;
 
   /***** Lower part of Fortran frontend *****/
-
-  const char *LowerExec = Args.MakeArgString(getToolChain().GetProgramPath("flang2"));
+  std::string flang2 = "flang2";
+  if (getToolChain().isCrossCompiling())
+    flang2 = getToolChain().getEffectiveTriple().getTriple() + "-" + flang2;
+  const char *LowerExec =
+      Args.MakeArgString(getToolChain().GetProgramPath(flang2.c_str()));
 
   // TODO FLANG arg handling
   LowerCmdArgs.push_back("-fn"); LowerCmdArgs.push_back(Input.getBaseInput());

clang/lib/Driver/ToolChains/Linux.cpp

@@ -666,7 +666,11 @@ void Linux::AddFlangSystemIncludeArgs(const ArgList &DriverArgs,
 
   {
     SmallString<128> P(D.Dir);
-    llvm::sys::path::append(P, "../include");
+    if (isCrossCompiling())
+      llvm::sys::path::append(P, "../include",
+                              getEffectiveTriple().getTriple());
+    else
+      llvm::sys::path::append(P, "../include");
     IncludePathList.push_back(P.c_str());
   }
 

clang/test/Driver/flang/classic-flang-cross-compile.F95

@@ -0,0 +1,15 @@
+! REQUIRES: classic_flang
+! REQUIRES: host-x86_64
+
+! Check if the cross-compiling flang1/flang2 binaries and include paths
+! are used by Clang when cross-compiling.
+
+! RUN: %clang --driver-mode=flang -target aarch64-unknown-linux-gnu %s -### 2>&1 \
+! RUN:   | FileCheck %s
+
+! RUN: %clang --driver-mode=flang -target aarch64-linux-gnu %s -### 2>&1 \
+! RUN:   | FileCheck %s
+
+! CHECK: aarch64-unknown-linux-gnu-flang1
+! CHECK-SAME: include/aarch64-unknown-linux-gnu
+! CHECK: aarch64-unknown-linux-gnu-flang2

clang/test/lit.cfg.py

@@ -370,3 +370,5 @@ def calculate_arch_features(arch_string):
 
 if config.use_classic_flang:
     config.available_features.add("classic_flang")
+
+config.available_features.add("host-" + config.host_arch)