Do not generate calls to fentry with __attribute__((no_instrument_function))

[manojgupta]

Summary

Currently only calls to mcount were suppressed with
no_instrument_function attribute.
Linux kernel requires that calls to fentry should also not be
generated.
This is an extended fix for PR PR33515.

[chandlerc]

Adding more Clang CodeGen folks to this review rather than myself...

[rnk]

This looks right to me, but we should check with @hans since I think he touched this code last.

[rjmccall]

Seems reasonable to me.

lib/CodeGen/CodeGenFunction.cpp

if (CGM.getCodeGenOpts().InstrumentFunctionEntryBare)
                        "__cyg_profile_func_enter_bare");
   }
 
   // Since emitting the mcount call here impacts optimizations such as function
   // inlining, we just add an attribute to insert a mcount call in backend.
   // The attribute "counting-function" is set to mcount function name which is
   // architecture dependent.
   if (CGM.getCodeGenOpts().InstrumentForProfiling) {
+    // Calls to fentry/mcount should not be generated if function has
+    // the no_instrument_function attribute.
+    if (!CurFuncDecl || !CurFuncDecl->hasAttr<NoInstrumentFunctionAttr>()) {
       if (CGM.getCodeGenOpts().CallFEntry)
         Fn->addFnAttr("fentry-call", "true");
       else {
-      if (!CurFuncDecl || !CurFuncDecl->hasAttr<NoInstrumentFunctionAttr>()) {
         Fn->addFnAttr("instrument-function-entry-inlined",
                       getTarget().getMCountName());
       }
     }
   }
 
   if (RetTy->isVoidType()) {
     // Void type; nothing to return.

test/CodeGen/fentry.c

 // RUN: %clang_cc1 -pg -mfentry -triple i386-unknown-unknown -emit-llvm -o - %s | FileCheck  %s
 // RUN: %clang_cc1 -pg -mfentry -triple x86_64-unknown-linux-gnu -emit-llvm -o - %s | FileCheck %s
 // RUN: %clang_cc1 -mfentry -triple i386-unknown-unknown -emit-llvm -o - %s | FileCheck -check-prefix=NOPG %s
 // RUN: %clang_cc1 -mfentry -triple x86_64-unknown-linux-gnu -emit-llvm -o - %s | FileCheck -check-prefix=NOPG %s
 
 int foo(void) {
   return 0;
 }
 
-//CHECK: attributes #{{[0-9]+}} = { {{.*}}"fentry-call"="true"{{.*}} }
-//NOPG-NOT: attributes #{{[0-9]+}} = { {{.*}}"fentry-call"{{.*}} }
+int __attribute__((no_instrument_function)) no_instrument(void) {
+  return foo();
+}
+
+//CHECK: attributes #0 = { {{.*}}"fentry-call"="true"{{.*}} }
+//CHECK: attributes #1 = { {{.*}} }
+//CHECK-NOT: attributes #1 = { {{.*}}"fentry-call"="true"{{.*}} }
+//NOPG-NOT: attributes #0 = { {{.*}}"fentry-call"{{.*}} }
+//NOPG-NOT: attributes #1 = { {{.*}}"fentry-call"{{.*}} }