Add -finstrument-function-entry-bare flag

This is an instrumentation flag that's similar to
-finstrument-functions, but it only inserts calls on function entry, the
calls are inserted post-inlining, and they don't take any arugments.

This is intended for users who want to instrument function entry with
minimal overhead.

(-pg would be another alternative, but forces frame pointer emission and
affects link flags, so is probably best left alone to be used for
generating gcov data.)

Differential revision: https://reviews.llvm.org/D40276

llvm-svn: 318785

clang/include/clang/Driver/Options.td

@@ -1030,6 +1030,8 @@ def finstrument_functions : Flag<["-"], "finstrument-functions">, Group<f_Group>
   HelpText<"Generate calls to instrument function entry and exit">;
 def finstrument_functions_after_inlining : Flag<["-"], "finstrument-functions-after-inlining">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Like -finstrument-functions, but insert the calls after inlining">;
+def finstrument_function_entry_bare : Flag<["-"], "finstrument-function-entry-bare">, Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Instrument function entry only, after inlining, without arguments to the instrumentation call">;
 
 def fxray_instrument : Flag<["-"], "fxray-instrument">, Group<f_Group>,
   Flags<[CC1Option]>,

clang/include/clang/Frontend/CodeGenOptions.def

@@ -78,6 +78,8 @@ CODEGENOPT(InstrumentFunctions , 1, 0) ///< Set when -finstrument-functions is
                                        ///< enabled.
 CODEGENOPT(InstrumentFunctionsAfterInlining , 1, 0) ///< Set when
                           ///< -finstrument-functions-after-inlining is enabled.
+CODEGENOPT(InstrumentFunctionEntryBare , 1, 0) ///< Set when
+                               ///< -finstrument-function-entry-bare is enabled.
 
 CODEGENOPT(XRayInstrumentFunctions , 1, 0) ///< Set when -fxray-instrument is
                                            ///< enabled.

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -355,10 +355,11 @@ void CodeGenFunction::FinishFunction(SourceLocation EndLoc) {
   llvm::DebugLoc Loc = EmitReturnBlock();
 
   if (ShouldInstrumentFunction()) {
-    CurFn->addFnAttr(!CGM.getCodeGenOpts().InstrumentFunctionsAfterInlining
-                         ? "instrument-function-exit"
-                         : "instrument-function-exit-inlined",
-                     "__cyg_profile_func_exit");
+    if (CGM.getCodeGenOpts().InstrumentFunctions)
+      CurFn->addFnAttr("instrument-function-exit", "__cyg_profile_func_exit");
+    if (CGM.getCodeGenOpts().InstrumentFunctionsAfterInlining)
+      CurFn->addFnAttr("instrument-function-exit-inlined",
+                       "__cyg_profile_func_exit");
   }
 
   // Emit debug descriptor for function end.
@@ -443,7 +444,8 @@ void CodeGenFunction::FinishFunction(SourceLocation EndLoc) {
 /// instrumented with __cyg_profile_func_* calls
 bool CodeGenFunction::ShouldInstrumentFunction() {
   if (!CGM.getCodeGenOpts().InstrumentFunctions &&
-      !CGM.getCodeGenOpts().InstrumentFunctionsAfterInlining)
+      !CGM.getCodeGenOpts().InstrumentFunctionsAfterInlining &&
+      !CGM.getCodeGenOpts().InstrumentFunctionEntryBare)
     return false;
   if (!CurFuncDecl || CurFuncDecl->hasAttr<NoInstrumentFunctionAttr>())
     return false;
@@ -982,10 +984,14 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
   }
 
   if (ShouldInstrumentFunction()) {
-    Fn->addFnAttr(!CGM.getCodeGenOpts().InstrumentFunctionsAfterInlining
-                      ? "instrument-function-entry"
-                      : "instrument-function-entry-inlined",
-                  "__cyg_profile_func_enter");
+    if (CGM.getCodeGenOpts().InstrumentFunctions)
+      CurFn->addFnAttr("instrument-function-entry", "__cyg_profile_func_enter");
+    if (CGM.getCodeGenOpts().InstrumentFunctionsAfterInlining)
+      CurFn->addFnAttr("instrument-function-entry-inlined",
+                       "__cyg_profile_func_enter");
+    if (CGM.getCodeGenOpts().InstrumentFunctionEntryBare)
+      CurFn->addFnAttr("instrument-function-entry-inlined",
+                       "__cyg_profile_func_enter_bare");
   }
 
   // Since emitting the mcount call here impacts optimizations such as function

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3554,8 +3554,11 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                     options::OPT_fno_unique_section_names, true))
     CmdArgs.push_back("-fno-unique-section-names");
 
-  Args.AddLastArg(CmdArgs, options::OPT_finstrument_functions,
-                  options::OPT_finstrument_functions_after_inlining);
+  if (auto *A = Args.getLastArg(
+      options::OPT_finstrument_functions,
+      options::OPT_finstrument_functions_after_inlining,
+      options::OPT_finstrument_function_entry_bare))
+    A->render(Args, CmdArgs);
 
   addPGOAndCoverageFlags(C, D, Output, Args, CmdArgs);
 

clang/lib/Frontend/CompilerInvocation.cpp

@@ -782,6 +782,8 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.InstrumentFunctions = Args.hasArg(OPT_finstrument_functions);
   Opts.InstrumentFunctionsAfterInlining =
       Args.hasArg(OPT_finstrument_functions_after_inlining);
+  Opts.InstrumentFunctionEntryBare =
+      Args.hasArg(OPT_finstrument_function_entry_bare);
   Opts.XRayInstrumentFunctions = Args.hasArg(OPT_fxray_instrument);
   Opts.XRayInstructionThreshold =
       getLastArgIntValue(Args, OPT_fxray_instruction_threshold_EQ, 200, Diags);

clang/test/CodeGen/instrument-functions.c

@@ -1,8 +1,12 @@
 // RUN: %clang_cc1 -S -debug-info-kind=standalone -emit-llvm -o - %s -finstrument-functions -disable-llvm-passes | FileCheck %s
+// RUN: %clang_cc1 -S -debug-info-kind=standalone -emit-llvm -o - %s -finstrument-function-entry-bare -disable-llvm-passes | FileCheck -check-prefix=BARE %s
 
 int test1(int x) {
 // CHECK: @test1(i32 {{.*}}%x) #[[ATTR1:[0-9]+]]
 // CHECK: ret
+
+// BARE: @test1(i32 {{.*}}%x) #[[ATTR1:[0-9]+]]
+// BARE: ret
   return x;
 }
 
@@ -10,6 +14,9 @@ int test2(int) __attribute__((no_instrument_function));
 int test2(int x) {
 // CHECK: @test2(i32 {{.*}}%x) #[[ATTR2:[0-9]+]]
 // CHECK: ret
+
+// BARE: @test2(i32 {{.*}}%x) #[[ATTR2:[0-9]+]]
+// BARE: ret
   return x;
 }
 
@@ -17,5 +24,11 @@ int test2(int x) {
 // CHECK-SAME: "instrument-function-entry"="__cyg_profile_func_enter"
 // CHECK-SAME: "instrument-function-exit"="__cyg_profile_func_exit"
 
+// BARE: attributes #[[ATTR1]] =
+// BARE-SAME: "instrument-function-entry-inlined"="__cyg_profile_func_enter_bare"
+
 // CHECK: attributes #[[ATTR2]] =
 // CHECK-NOT: "instrument-function-entry"
+
+// BARE: attributes #[[ATTR2]] =
+// BARE-NOT: "instrument-function-entry"