[PATCH] D104475: [Clang][Codegen] emit noprofile IR Fn Attr for new Fn Attr no_profile

[Nick Desaulniers via Phabricator via cfe-commits]

nickdesaulniers created this revision.
nickdesaulniers added reviewers: MaskRay, melver, void, davidxl, vsk, phosek.
Herald added a reviewer: aaron.ballman.
Herald added subscribers: wenlei, jdoerfert.
nickdesaulniers requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

noprofile IR attribute already exists to prevent profiling with PGO;
emit that when a function uses the newly added no_profile function
attribute.

The Linux kernel would like to avoid compiler generated code in
functions annotated with such attribute. We already respect this for
libcalls to fentry() and mcount().

Alternate implementation to: https://reviews.llvm.org/D104253
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80223
Link: https://lore.kernel.org/lkml/CAKwvOdmPTi93n2L0_yQkrzLdmpxzrOR7zggSzonyaw2PGshApw@mail.gmail.com/


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D104475

Files:
  clang/include/clang/Basic/Attr.td
  clang/include/clang/Basic/AttrDocs.td
  clang/lib/CodeGen/CodeGenFunction.cpp
  clang/test/CodeGen/fprofile.c
  clang/test/Misc/pragma-attribute-supported-attributes-list.test


Index: clang/test/Misc/pragma-attribute-supported-attributes-list.test
===================================================================
--- clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -99,6 +99,7 @@
 // CHECK-NEXT: NoMerge (SubjectMatchRule_function)
 // CHECK-NEXT: NoMicroMips (SubjectMatchRule_function)
 // CHECK-NEXT: NoMips16 (SubjectMatchRule_function)
+// CHECK-NEXT: NoProfileFunction (SubjectMatchRule_function)
 // CHECK-NEXT: NoSanitize (SubjectMatchRule_function, SubjectMatchRule_objc_method, SubjectMatchRule_variable_is_global)
 // CHECK-NEXT: NoSanitizeSpecific (SubjectMatchRule_function, SubjectMatchRule_variable_is_global)
 // CHECK-NEXT: NoSpeculativeLoadHardening (SubjectMatchRule_function, SubjectMatchRule_objc_method)
Index: clang/test/CodeGen/fprofile.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/fprofile.c
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -fprofile-instrument=llvm -disable-llvm-passes \
+// RUN:   -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -fprofile-instrument=csllvm -disable-llvm-passes \
+// RUN:   -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -fprofile-instrument=clang -disable-llvm-passes \
+// RUN:   -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -fprofile-arcs -disable-llvm-passes \
+// RUN:   -emit-llvm -o - %s | FileCheck %s
+int g(int);
+
+void __attribute__((no_profile)) no_instr() {
+// CHECK: define {{.*}} void @no_instr() [[ATTR:#[0-9]+]]
+}
+
+void instr(void) {
+// CHECK: define {{.*}} void @instr() [[ATTR2:#[0-9]+]]
+}
+// CHECK: attributes [[ATTR]] = {{.*}} noprofile
+// CHECK-NOT: attributes [[ATTR2]] = {{.*}} noprofile
Index: clang/lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenFunction.cpp
+++ clang/lib/CodeGen/CodeGenFunction.cpp
@@ -893,6 +893,9 @@
   if (D && D->hasAttr<CFICanonicalJumpTableAttr>())
     Fn->addFnAttr("cfi-canonical-jump-table");
 
+  if (D && D->hasAttr<NoProfileFunctionAttr>())
+    Fn->addFnAttr(llvm::Attribute::NoProfile);
+
   if (getLangOpts().OpenCL) {
     // Add metadata for a kernel function.
     if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D))
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -2559,6 +2559,17 @@
   }];
 }
 
+def NoProfileDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+Use the ``no_profile`` attribute on a function to declaration to denote that
+the compiler should not instrument the function with profile related
+instrumentation, such as via the
+``-fprofile-generate`` / ``-fprofile-instr-generate`` /
+``-fcs-profile-generate`` / ``-fprofile-arcs`` flags.
+}];
+}
+
 def NoSanitizeDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -1970,6 +1970,13 @@
   let SimpleHandler = 1;
 }
 
+def NoProfileFunction : InheritableAttr {
+  let Spellings = [GCC<"no_profile">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [NoProfileDocs];
+  let SimpleHandler = 1;
+}
+
 def NotTailCalled : InheritableAttr {
   let Spellings = [Clang<"not_tail_called">];
   let Subjects = SubjectList<[Function]>;


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