Add the -ffixed-r9 flag for ARM.

This patch adds the -ffixed-r9 flag to clang to instruct llvm to
globally preserve the contents of r9. The flag is added to the newly
created ARM specific group.

While at it, also place marm / mno-thumb in that group.

Patch by Jeroen Hofstee.

llvm-svn: 189174

Author: rengolin

clang/include/clang/Driver/Options.td

@@ -72,6 +72,7 @@ def clang_i_Group         : OptionGroup<"<clang i group>">, Group<i_Group>;
 def m_Group               : OptionGroup<"<m group>">, Group<CompileOnly_Group>;
 def m_x86_Features_Group  : OptionGroup<"<m x86 features group>">, Group<m_Group>;
 def m_hexagon_Features_Group  : OptionGroup<"<m hexagon features group>">, Group<m_Group>;
+def m_arm_Features_Group  : OptionGroup<"<m arm features group>">, Group<m_Group>;
 def opencl_Group          : OptionGroup<"<opencl group>">;
 def u_Group               : OptionGroup<"<u group>">;
 def mips_CPUs_Group       : OptionGroup<"<MIPS CPU aliases group>">,
@@ -986,8 +987,10 @@ def mno_rtm : Flag<["-"], "mno-rtm">, Group<m_x86_Features_Group>;
 def mno_prfchw : Flag<["-"], "mno-prfchw">, Group<m_x86_Features_Group>;
 def mno_rdseed : Flag<["-"], "mno-rdseed">, Group<m_x86_Features_Group>;
 
-def mno_thumb : Flag<["-"], "mno-thumb">, Group<m_Group>;
+def mno_thumb : Flag<["-"], "mno-thumb">, Group<m_arm_Features_Group>;
 def marm : Flag<["-"], "marm">, Alias<mno_thumb>;
+def ffixed_r9 : Flag<["-"], "ffixed-r9">, Group<m_arm_Features_Group>,
+  HelpText<"Reserve the r9 register (ARM only)">;
 
 def mno_warn_nonportable_cfstrings : Flag<["-"], "mno-warn-nonportable-cfstrings">, Group<m_Group>;
 def mno_omit_leaf_frame_pointer : Flag<["-"], "mno-omit-leaf-frame-pointer">, Group<m_Group>;

clang/lib/Driver/Tools.cpp

@@ -795,6 +795,14 @@ void Clang::AddARMTargetArgs(const ArgList &Args,
                     options::OPT_mno_implicit_float,
                     true))
     CmdArgs.push_back("-no-implicit-float");
+
+    // llvm does not support reserving registers in general. There is support
+    // for reserving r9 on ARM though (defined as a platform-specific register
+    // in ARM EABI).
+    if (Args.hasArg(options::OPT_ffixed_r9)) {
+      CmdArgs.push_back("-backend-option");
+      CmdArgs.push_back("-arm-reserve-r9");
+    }
 }
 
 // Translate MIPS CPU name alias option to CPU name.