[PATCH] D104253: [Clang][Codegen] emit noprofile IR Fn Attr for no_instrument_function Fn Attr

[Nick Desaulniers via Phabricator via cfe-commits]

nickdesaulniers created this revision.
nickdesaulniers added reviewers: MaskRay, melver, void.
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noprofile IR attribute already exists to prevent profiling with PGO;
emit that when a function uses the no_instrument_function 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().

Link: https://lore.kernel.org/lkml/CAKwvOdmPTi93n2L0_yQkrzLdmpxzrOR7zggSzonyaw2PGshApw@mail.gmail.com/
Signed-off-by: Nick Desaulniers <ndesaulniers at google.com>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D104253

Files:
  clang/lib/CodeGen/CodeGenFunction.cpp
  clang/test/CodeGen/fprofile-generate.c


Index: clang/test/CodeGen/fprofile-generate.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/fprofile-generate.c
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -fprofile-instrument=llvm -emit-llvm -o - %s | FileCheck %s
+int g(int);
+
+int __attribute__((__no_instrument_function__))
+__attribute__((no_instrument_function))
+no_instr(int a) {
+// CHECK: define {{.*}} i32 @no_instr(i32 %a) [[ATTR:#[0-9]+]]
+  int sum = 0;
+  for (int i = 0; i < a; i++)
+    sum += g(i);
+  return sum;
+}
+
+int instr(int a) {
+// CHECK: define {{.*}} i32 @instr(i32 %a) [[ATTR2:#[0-9]+]]
+  int sum = 0;
+  for (int i = 0; i < a; i++)
+    sum += g(i);
+  return sum;
+}
+// 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<NoInstrumentFunctionAttr>())
+    Fn->addFnAttr(llvm::Attribute::NoProfile);
+
   if (getLangOpts().OpenCL) {
     // Add metadata for a kernel function.
     if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D))


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