[XRay][clang] Emit "never-instrument" attribute

Summary:
Before this change, we only emit the XRay attributes in LLVM IR when the
-fxray-instrument flag is provided. This may cause issues with thinlto
when the final binary is being built/linked with -fxray-instrument, and
the constitutent LLVM IR gets re-lowered with xray instrumentation.

With this change, we can honour the "never-instrument "attributes
provided in the source code and preserve those in the IR. This way, even
in thinlto builds, we retain the attributes which say whether functions
should never be XRay instrumented.

This change addresses llvm.org/PR38922.

Reviewers: mboerger, eizan

Subscribers: mehdi_amini, dexonsmith, cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D52015

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@342200 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 55 insertions, 22 deletions

diff --git a/lib/CodeGen/CodeGenFunction.cpp b/lib/CodeGen/CodeGenFunction.cpp
index d14275531c..77f978f687 100644
--- a/lib/CodeGen/CodeGenFunction.cpp
+++ b/lib/CodeGen/CodeGenFunction.cpp
@@ -901,21 +901,21 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
   }
 
   // Apply xray attributes to the function (as a string, for now)
-  bool InstrumentXray = ShouldXRayInstrumentFunction() &&
-                        CGM.getCodeGenOpts().XRayInstrumentationBundle.has(
-                            XRayInstrKind::Function);
-  if (D && InstrumentXray) {
+  if (D) {
     if (const auto *XRayAttr = D->getAttr<XRayInstrumentAttr>()) {
-      if (XRayAttr->alwaysXRayInstrument())
-        Fn->addFnAttr("function-instrument", "xray-always");
-      if (XRayAttr->neverXRayInstrument())
-        Fn->addFnAttr("function-instrument", "xray-never");
-      if (const auto *LogArgs = D->getAttr<XRayLogArgsAttr>()) {
-        Fn->addFnAttr("xray-log-args",
-                      llvm::utostr(LogArgs->getArgumentCount()));
+      if (CGM.getCodeGenOpts().XRayInstrumentationBundle.has(
+              XRayInstrKind::Function)) {
+        if (XRayAttr->alwaysXRayInstrument() && ShouldXRayInstrumentFunction())
+          Fn->addFnAttr("function-instrument", "xray-always");
+        if (XRayAttr->neverXRayInstrument())
+          Fn->addFnAttr("function-instrument", "xray-never");
+        if (const auto *LogArgs = D->getAttr<XRayLogArgsAttr>())
+          if (ShouldXRayInstrumentFunction())
+            Fn->addFnAttr("xray-log-args",
+                          llvm::utostr(LogArgs->getArgumentCount()));
       }
     } else {
-      if (!CGM.imbueXRayAttrs(Fn, Loc))
+      if (ShouldXRayInstrumentFunction() && !CGM.imbueXRayAttrs(Fn, Loc))
         Fn->addFnAttr(
             "xray-instruction-threshold",
             llvm::itostr(CGM.getCodeGenOpts().XRayInstructionThreshold));
diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 7df2ea714e..49c926db56 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -1967,9 +1967,6 @@ bool CodeGenModule::isInSanitizerBlacklist(llvm::GlobalVariable *GV,
 
 bool CodeGenModule::imbueXRayAttrs(llvm::Function *Fn, SourceLocation Loc,
                                    StringRef Category) const {
-  if (!LangOpts.XRayInstrument)
-    return false;
-
   const auto &XRayFilter = getContext().getXRayFilter();
   using ImbueAttr = XRayFunctionFilter::ImbueAttribute;
   auto Attr = ImbueAttr::NONE;
diff --git a/test/CodeGen/xray-attributes-noxray-supported.cpp b/test/CodeGen/xray-attributes-noxray-supported.cpp
new file mode 100644
index 0000000000..f9c8a2ee69
--- /dev/null
+++ b/test/CodeGen/xray-attributes-noxray-supported.cpp
@@ -0,0 +1,29 @@
+// We want to ensure that the "never instrument" attributes show up even if we
+// explicitly turn off XRay instrumentation.
+//
+// RUN: %clang_cc1 %s -fno-xray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple x86_64-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fno-xray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple arm-unknown-linux-gnu -target-abi apcs-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fno-xray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple mips-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fno-xray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple mipsel-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fno-xray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple mips64-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fno-xray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple mips64el-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fno-xray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple powerpc64le-unknown-linux-gnu | FileCheck %s
+
+[[clang::xray_always_instrument]] void foo() {
+// CHECK: define void @_Z3foov() #0
+}
+
+[[clang::xray_never_instrument]] void bar() {
+// CHECK: define void @_Z3barv() #1
+}
+
+// CHECK-NOT: #0 = {{.*}}"function-instrument"="xray-always"
+// CHECK: #1 = {{.*}}"function-instrument"="xray-never"
+
diff --git a/test/CodeGen/xray-attributes-supported.cpp b/test/CodeGen/xray-attributes-supported.cpp
index 21a5dde53a..51ee4721f2 100644
--- a/test/CodeGen/xray-attributes-supported.cpp
+++ b/test/CodeGen/xray-attributes-supported.cpp
@@ -1,10 +1,17 @@
-// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - -triple x86_64-unknown-linux-gnu | FileCheck %s
-// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - -triple arm-unknown-linux-gnu -target-abi apcs-gnu | FileCheck %s
-// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - -triple mips-unknown-linux-gnu | FileCheck %s
-// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - -triple mipsel-unknown-linux-gnu | FileCheck %s
-// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - -triple mips64-unknown-linux-gnu | FileCheck %s
-// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - -triple mips64el-unknown-linux-gnu | FileCheck %s
-// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - -triple powerpc64le-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple x86_64-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple arm-unknown-linux-gnu -target-abi apcs-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple mips-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple mipsel-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple mips64-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple mips64el-unknown-linux-gnu | FileCheck %s
+// RUN: %clang_cc1 %s -fxray-instrument -std=c++11 -x c++ -emit-llvm -o - \
+// RUN:     -triple powerpc64le-unknown-linux-gnu | FileCheck %s
 
 // Make sure that the LLVM attribute for XRay-annotated functions do show up.
 [[clang::xray_always_instrument]] void foo() {