[xray] Function coverage groups

Add the ability to selectively instrument a subset of functions by dividing the functions into N logical groups and then selecting a group to cover. By selecting different groups over time you could cover the entire application incrementally with lower overhead than instrumenting the entire application at once.

Differential Revision: https://reviews.llvm.org/D87953

1 files changed, 16 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 016c710..47ef5c8 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -32,6 +32,7 @@
 #include "clang/Basic/TargetInfo.h"
 #include "clang/CodeGen/CGFunctionInfo.h"
 #include "clang/Frontend/FrontendDiagnostic.h"
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/Frontend/OpenMP/OMPIRBuilder.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Dominators.h"
@@ -40,6 +41,7 @@
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Operator.h"
+#include "llvm/Support/CRC.h"
 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
 using namespace clang;
 using namespace CodeGen;
@@ -772,13 +774,16 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
         SanOpts.Mask &= ~SanitizerKind::Null;
 
   // Apply xray attributes to the function (as a string, for now)
+  bool AlwaysXRayAttr = false;
   if (const auto *XRayAttr = D ? D->getAttr<XRayInstrumentAttr>() : nullptr) {
     if (CGM.getCodeGenOpts().XRayInstrumentationBundle.has(
             XRayInstrKind::FunctionEntry) ||
         CGM.getCodeGenOpts().XRayInstrumentationBundle.has(
             XRayInstrKind::FunctionExit)) {
-      if (XRayAttr->alwaysXRayInstrument() && ShouldXRayInstrumentFunction())
+      if (XRayAttr->alwaysXRayInstrument() && ShouldXRayInstrumentFunction()) {
         Fn->addFnAttr("function-instrument", "xray-always");
+        AlwaysXRayAttr = true;
+      }
       if (XRayAttr->neverXRayInstrument())
         Fn->addFnAttr("function-instrument", "xray-never");
       if (const auto *LogArgs = D->getAttr<XRayLogArgsAttr>())
@@ -804,6 +809,16 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
     if (!CGM.getCodeGenOpts().XRayInstrumentationBundle.has(
             XRayInstrKind::FunctionEntry))
       Fn->addFnAttr("xray-skip-entry");
+
+    auto FuncGroups = CGM.getCodeGenOpts().XRayTotalFunctionGroups;
+    if (FuncGroups > 1) {
+      auto FuncName = llvm::makeArrayRef<uint8_t>(
+          CurFn->getName().bytes_begin(), CurFn->getName().bytes_end());
+      auto Group = crc32(FuncName) % FuncGroups;
+      if (Group != CGM.getCodeGenOpts().XRaySelectedFunctionGroup &&
+          !AlwaysXRayAttr)
+        Fn->addFnAttr("function-instrument", "xray-never");
+    }
   }
 
   unsigned Count, Offset;