[Clang FE] Recognize -mnop-mcount CL option (SystemZ only).

Recognize -mnop-mcount from the command line and add a function attribute
"mnop-mcount"="true" when passed.

When this option is used, a nop is added instead of a call to fentry. This
is used when 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/D67763

Author: JonPsson

clang/include/clang/Basic/CodeGenOptions.def

@@ -112,6 +112,7 @@ 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(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/Basic/DiagnosticCommonKinds.td

@@ -271,6 +271,8 @@ def err_target_unsupported_mcmse : Error<
   "-mcmse is not supported for %0">;
 def err_opt_not_valid_with_opt : Error<
   "option '%0' cannot be specified with '%1'">;
+def err_opt_not_valid_without_opt : Error<
+  "option '%0' cannot be specified without '%1'">;
 def err_opt_not_valid_on_target : Error<
   "option '%0' cannot be specified on this target">;
 

clang/include/clang/Driver/Options.td

@@ -2448,6 +2448,8 @@ def mpie_copy_relocations : Flag<["-"], "mpie-copy-relocations">, Group<m_Group>
 def mno_pie_copy_relocations : Flag<["-"], "mno-pie-copy-relocations">, Group<m_Group>;
 def mfentry : Flag<["-"], "mfentry">, HelpText<"Insert calls to fentry at function entry (x86/SystemZ only)">,
   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 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

@@ -893,6 +893,16 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
         Fn->addFnAttr("instrument-function-entry-inlined",
                       getTarget().getMCountName());
       }
+      if (CGM.getCodeGenOpts().MNopMCount) {
+        if (getContext().getTargetInfo().getTriple().getArch() !=
+            llvm::Triple::systemz)
+          CGM.getDiags().Report(diag::err_opt_not_valid_on_target)
+            << "-mnop-mcount";
+        if (!CGM.getCodeGenOpts().CallFEntry)
+          CGM.getDiags().Report(diag::err_opt_not_valid_without_opt)
+            << "-mnop-mcount" << "-mfentry";
+        Fn->addFnAttr("mnop-mcount", "true");
+      }
     }
   }
 

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4616,6 +4616,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (TC.SupportsProfiling())
     Args.AddLastArg(CmdArgs, options::OPT_mfentry);
 
+  if (TC.SupportsProfiling())
+    Args.AddLastArg(CmdArgs, options::OPT_mnop_mcount);
+
   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

@@ -1103,6 +1103,7 @@ 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.EmitOpenCLArgMetadata = Args.hasArg(OPT_cl_kernel_arg_info);
 
   if (const Arg *A = Args.getLastArg(OPT_fcf_protection_EQ)) {

clang/test/CodeGen/mnop-mcount.c

@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -pg -mfentry -mnop-mcount -triple s390x-ibm-linux -emit-llvm \
+// RUN:   -o - %s 2>&1 | FileCheck  %s
+// RUN: not %clang_cc1 -pg -mnop-mcount -triple s390x-ibm-linux -emit-llvm -o - \
+// RUN:   %s 2>&1 | FileCheck -check-prefix=NOMFENTRY %s
+// RUN: %clang_cc1 -mfentry -mnop-mcount -triple s390x-ibm-linux -emit-llvm -o - \
+// RUN:   %s 2>&1 | FileCheck -check-prefix=NOPG %s
+// RUN: %clang_cc1 -mnop-mcount -triple s390x-ibm-linux -emit-llvm -o - %s \
+// RUN:   2>&1 | FileCheck -check-prefix=NOPG %s
+// RUN: not %clang_cc1 -pg -mfentry -mnop-mcount -triple x86_64-linux-gnu \
+// RUN:   -emit-llvm -o - %s 2>&1 | FileCheck -check-prefix=X86 %s
+
+int foo(void) {
+  return 0;
+}
+
+int __attribute__((no_instrument_function)) no_instrument(void) {
+  return foo();
+}
+
+//CHECK: attributes #0 = { {{.*}}"mnop-mcount"="true"{{.*}} }
+//CHECK: attributes #1 = { {{.*}} }
+//CHECK-NOT: attributes #1 = { {{.*}}"mnop-mcount"="true"{{.*}} }
+//NOMFENTRY: error: option '-mnop-mcount' cannot be specified without '-mfentry'
+//NOPG-NOT: attributes #0 = { {{.*}}"mnop-mcount"{{.*}} }
+//NOPG-NOT: attributes #1 = { {{.*}}"mnop-mcount"{{.*}} }
+//X86: error: option '-mnop-mcount' cannot be specified on this target