[clang][xray] Add -fxray-ignore-loops option

[ianlevesque]

Summary

XRay allows tuning by minimum function size, but also always instruments
functions with loops in them. If the minimum function size is set to a
large value the loop instrumention ends up causing most functions to be
instrumented anyway. This adds a new flag, -fxray-ignore-loops, to disable
the loop detection logic.

The LLVM change to take the new function attribute into account is in D72659

[ianlevesque]

fix clang-format

[hiraditya]

clang/lib/CodeGen/CodeGenFunction.cpp

821

we can remove braces here.

clang/test/CodeGen/xray-ignore-loops.cpp

6

I think we need one more test case of a function having a loop.

[ianlevesque]

clang/test/CodeGen/xray-ignore-loops.cpp

6

I'm not opposed but the logic to actually ignore loops has a test on D72659

[hiraditya]

The test case is in another patch so LGTM.

clang/include/clang/Basic/CodeGenOptions.def

CODEGENOPT(ForceDwarfFrameSection , 1, 0) ///< Set when -fforce-dwarf-frame is
                                           ///< enabled.
 
 ///< Set when -fxray-always-emit-customevents is enabled.
 CODEGENOPT(XRayAlwaysEmitCustomEvents , 1, 0)
 
 ///< Set when -fxray-always-emit-typedevents is enabled.
 CODEGENOPT(XRayAlwaysEmitTypedEvents , 1, 0)
 
+///< Set when -fxray-ignore-loops is enabled.
+CODEGENOPT(XRayIgnoreLoops , 1, 0)
+
+
 ///< Set the minimum number of instructions in a function to determine selective
 ///< XRay instrumentation.
 VALUE_CODEGENOPT(XRayInstructionThreshold , 32, 200)
 
 VALUE_CODEGENOPT(PatchableFunctionEntryCount , 32, 0) ///< Number of NOPs at function entry
 
 CODEGENOPT(InstrumentForProfiling , 1, 0) ///< Set when -pg is enabled.
 CODEGENOPT(CallFEntry , 1, 0) ///< Set when -mfentry is enabled.

clang/include/clang/Driver/Options.td

def fnoxray_always_emit_customevents : Flag<["-"], "fno-xray-always-emit-customevents">, Group<f_Group>,
   Flags<[CC1Option]>;
 
 def fxray_always_emit_typedevents : Flag<["-"], "fxray-always-emit-typedevents">, Group<f_Group>,
   Flags<[CC1Option]>,
   HelpText<"Determine whether to always emit __xray_typedevent(...) calls even if the function it appears in is not always instrumented.">;
 def fnoxray_always_emit_typedevents : Flag<["-"], "fno-xray-always-emit-typedevents">, Group<f_Group>,
   Flags<[CC1Option]>;
 
+def fxray_ignore_loops : Flag<["-"], "fxray-ignore-loops">, Group<f_Group>,
+  Flags<[CC1Option]>,
+  HelpText<"Don't instrument functions with loops unless they also meet the minimum function size">;
+def fno_xray_ignore_loops : Flag<["-"], "fno-xray-ignore-loops">, Group<f_Group>,
+  Flags<[CC1Option]>;
+
+
 def fxray_link_deps : Flag<["-"], "fxray-link-deps">, Group<f_Group>,
   Flags<[CC1Option]>,
   HelpText<"Tells clang to add the link dependencies for XRay.">;
 def fnoxray_link_deps : Flag<["-"], "fnoxray-link-deps">, Group<f_Group>,
   Flags<[CC1Option]>;
 
 def fxray_instrumentation_bundle :
   JoinedOrSeparate<["-"], "fxray-instrumentation-bundle=">,

clang/lib/CodeGen/CodeGenFunction.cpp

if (const auto *XRayAttr = D->getAttr<XRayInstrumentAttr>()) {
             Fn->addFnAttr("xray-log-args",
                           llvm::utostr(LogArgs->getArgumentCount()));
       }
     } else {
       if (ShouldXRayInstrumentFunction() && !CGM.imbueXRayAttrs(Fn, Loc))
         Fn->addFnAttr(
             "xray-instruction-threshold",
             llvm::itostr(CGM.getCodeGenOpts().XRayInstructionThreshold));
+      if (CGM.getCodeGenOpts().XRayIgnoreLoops) {
+        Fn->addFnAttr("xray-ignore-loops");
+      }
     }
 
     if (const auto *Attr = D->getAttr<PatchableFunctionEntryAttr>()) {
       // Attr->getStart is currently ignored.
       Fn->addFnAttr("patchable-function-entry",
                     std::to_string(Attr->getCount()));
     } else if (unsigned Count = CGM.getCodeGenOpts().PatchableFunctionEntryCount) {
       Fn->addFnAttr("patchable-function-entry",

clang/lib/Frontend/CompilerInvocation.cpp

static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.XRayInstrumentFunctions =
       Args.hasArg(OPT_fxray_instrument);
   Opts.XRayAlwaysEmitCustomEvents =
       Args.hasArg(OPT_fxray_always_emit_customevents);
   Opts.XRayAlwaysEmitTypedEvents =
       Args.hasArg(OPT_fxray_always_emit_typedevents);
   Opts.XRayInstructionThreshold =
       getLastArgIntValue(Args, OPT_fxray_instruction_threshold_EQ, 200, Diags);
+  Opts.XRayIgnoreLoops =
+      Args.hasArg(OPT_fxray_ignore_loops, OPT_fno_xray_ignore_loops, false);
 
   auto XRayInstrBundles =
       Args.getAllArgValues(OPT_fxray_instrumentation_bundle);
   if (XRayInstrBundles.empty())
     Opts.XRayInstrumentationBundle.Mask = XRayInstrKind::All;
   else
     for (const auto &A : XRayInstrBundles)
       parseXRayInstrumentationBundle("-fxray-instrumentation-bundle=", A, Args,

clang/test/CodeGen/xray-ignore-loops.cpp

+// RUN: %clang_cc1 -fxray-instrument -fxray-ignore-loops -x c++ -std=c++11 -emit-llvm -o - %s -triple x86_64-unknown-linux-gnu | FileCheck %s
+
+int foo() {
+  return 1;
+}
+
+// CHECK: define i32 @_Z3foov() #[[ATTRS:[0-9]+]] {
+// CHECK-DAG: attributes #[[ATTRS]] = {{.*}} "xray-ignore-loops" {{.*}}