[Clang][Driver] Add an option to control loop-interchange

This introduces options -floop-interchange and -fno-loop-interchange to
enable/disable the loop-interchange pass. This is part of the work that
tries to get that pass enabled by default (#124911), where it was
remarked that a user facing option to control this would be convenient
to have. The option (name) is the same as GCC's.

Author: sjoerdmeijer

clang/include/clang/Driver/Options.td

@@ -4073,6 +4073,9 @@ defm assumptions : BoolFOption<"assumptions",
           "Disable codegen and compile-time checks for C++23's [[assume]] attribute">,
   PosFlag<SetTrue>>;
 
+def floop_interchange : Flag<["-"], "floop-interchange">, Group<f_Group>,
+  HelpText<"Enable the loop interchange pass">;
+def fno_loop_interchange: Flag<["-"], "fno-loop-interchange">, Group<f_Group>;
 def fvectorize : Flag<["-"], "fvectorize">, Group<f_Group>,
   HelpText<"Enable the loop vectorization passes">;
 def fno_vectorize : Flag<["-"], "fno-vectorize">, Group<f_Group>;

clang/lib/Driver/ToolChains/Clang.cpp

@@ -7619,6 +7619,16 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   Args.addOptOutFlag(CmdArgs, options::OPT_fgnu_inline_asm,
                      options::OPT_fno_gnu_inline_asm);
 
+  // Handle -floop-interchange
+  if (Arg *A = Args.getLastArg(options::OPT_floop_interchange,
+                               options::OPT_fno_loop_interchange)) {
+    CmdArgs.push_back("-mllvm");
+    if (A->getOption().matches(options::OPT_floop_interchange))
+      CmdArgs.push_back("-enable-loopinterchange=true");
+    else
+      CmdArgs.push_back("-enable-loopinterchange=false");
+  }
+
   // Enable vectorization per default according to the optimization level
   // selected. For optimization levels that want vectorization we use the alias
   // option to simplify the hasFlag logic.

clang/test/Driver/clang_f_opts.c

@@ -156,6 +156,13 @@
 // CHECK-VECTORIZE: "-vectorize-loops"
 // CHECK-NO-VECTORIZE-NOT: "-vectorize-loops"
 
+// RUN: %clang -### -S -floop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-INTERCHANGE %s
+// RUN: %clang -### -S -fno-loop-interchange -floop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-INTERCHANGE %s
+// RUN: %clang -### -S -fno-loop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-NO-INTERCHANGE %s
+// RUN: %clang -### -S -floop-interchange -fno-loop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-NO-INTERCHANGE %s
+// CHECK-INTERCHANGE: "-mllvm" "-enable-loopinterchange=true"
+// CHECK-NO-INTERCHANGE: "-mllvm" "-enable-loopinterchange=false"
+
 // RUN: %clang -### -S -fslp-vectorize %s 2>&1 | FileCheck -check-prefix=CHECK-SLP-VECTORIZE %s
 // RUN: %clang -### -S -fno-slp-vectorize -fslp-vectorize %s 2>&1 | FileCheck -check-prefix=CHECK-SLP-VECTORIZE %s
 // RUN: %clang -### -S -fno-slp-vectorize %s 2>&1 | FileCheck -check-prefix=CHECK-NO-SLP-VECTORIZE %s