[Clang FE, SystemZ] Recognize -mpacked-stack CL option

Recognize -mpacked-stack from the command line and add a function attribute
"mpacked-stack" when passed. This is needed for building the Linux kernel.

If this option is passed for any other target than SystemZ, an error is
generated.

Review: Ulrich Weigand
https://reviews.llvm.org/D71441

clang/include/clang/Basic/CodeGenOptions.def

@@ -113,6 +113,7 @@ VALUE_CODEGENOPT(XRayInstructionThreshold , 32, 200)
 CODEGENOPT(InstrumentForProfiling , 1, 0) ///< Set when -pg is enabled.
 CODEGENOPT(CallFEntry , 1, 0) ///< Set when -mfentry is enabled.
 CODEGENOPT(MNopMCount , 1, 0) ///< Set when -mnop-mcount is enabled.
+CODEGENOPT(PackedStack , 1, 0) ///< Set when -mpacked-stack is enabled.
 CODEGENOPT(LessPreciseFPMAD  , 1, 0) ///< Enable less precise MAD instructions to
                                      ///< be generated.
 CODEGENOPT(PrepareForLTO     , 1, 0) ///< Set when -flto is enabled on the

clang/include/clang/Driver/Options.td

@@ -2474,6 +2474,8 @@ def mfentry : Flag<["-"], "mfentry">, HelpText<"Insert calls to fentry at functi
   Flags<[CC1Option]>, Group<m_Group>;
 def mnop_mcount : Flag<["-"], "mnop-mcount">, HelpText<"Generate mcount/__fentry__ calls as nops. To activate they need to be patched in.">,
   Flags<[CC1Option]>, Group<m_Group>;
+def mpacked_stack : Flag<["-"], "mpacked-stack">, HelpText<"Use packed stack layout (SystemZ only).">,
+  Flags<[CC1Option]>, Group<m_Group>;
 def mips16 : Flag<["-"], "mips16">, Group<m_mips_Features_Group>;
 def mno_mips16 : Flag<["-"], "mno-mips16">, Group<m_mips_Features_Group>;
 def mmicromips : Flag<["-"], "mmicromips">, Group<m_mips_Features_Group>;

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -971,6 +971,14 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
     }
   }
 
+  if (CGM.getCodeGenOpts().PackedStack) {
+    if (getContext().getTargetInfo().getTriple().getArch() !=
+        llvm::Triple::systemz)
+      CGM.getDiags().Report(diag::err_opt_not_valid_on_target)
+        << "-mpacked-stack";
+    Fn->addFnAttr("packed-stack");
+  }
+
   if (RetTy->isVoidType()) {
     // Void type; nothing to return.
     ReturnValue = Address::invalid();

clang/lib/Driver/ToolChains/Clang.cpp

@@ -5014,6 +5014,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (TC.SupportsProfiling())
     Args.AddLastArg(CmdArgs, options::OPT_mnop_mcount);
 
+  Args.AddLastArg(CmdArgs, options::OPT_mpacked_stack);
+
   if (Args.getLastArg(options::OPT_fapple_kext) ||
       (Args.hasArg(options::OPT_mkernel) && types::isCXX(InputType)))
     CmdArgs.push_back("-fapple-kext");

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1104,6 +1104,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.InstrumentForProfiling = Args.hasArg(OPT_pg);
   Opts.CallFEntry = Args.hasArg(OPT_mfentry);
   Opts.MNopMCount = Args.hasArg(OPT_mnop_mcount);
+  Opts.PackedStack = Args.hasArg(OPT_mpacked_stack);
   Opts.EmitOpenCLArgMetadata = Args.hasArg(OPT_cl_kernel_arg_info);
 
   if (const Arg *A = Args.getLastArg(OPT_fcf_protection_EQ)) {

clang/test/CodeGen/packed-stack.c

@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -mpacked-stack -triple s390x-ibm-linux -emit-llvm \
+// RUN:   -o - %s 2>&1 | FileCheck  %s
+// RUN: not %clang_cc1 -mpacked-stack -triple x86_64-linux-gnu \
+// RUN:   -emit-llvm -o - %s 2>&1 | FileCheck -check-prefix=X86 %s
+
+int foo(void) {
+  return 0;
+}
+
+//CHECK: attributes #0 = { {{.*}}"packed-stack" {{.*}} }
+//X86: error: option '-mpacked-stack' cannot be specified on this target