[CodeGen] Attach no-builtin attributes to function definitions with no Decl

When using -fno-builtin[-<name>], we don't attach the IR attributes to
function definitions with no Decl, like the ones created through
`CreateGlobalInitOrDestructFunction`.

This results in projects using -fno-builtin or -ffreestanding to start
seeing symbols like _memset_pattern16.

The fix changes the behavior to always add the attribute if LangOptions
requests it.

Differential Revision: https://reviews.llvm.org/D73495

Author: francisvm

clang/lib/CodeGen/CGCall.cpp

@@ -1832,6 +1832,42 @@ void CodeGenModule::AddDefaultFnAttrs(llvm::Function &F) {
   F.addAttributes(llvm::AttributeList::FunctionIndex, FuncAttrs);
 }
 
+static void addNoBuiltinAttributes(llvm::AttrBuilder &FuncAttrs,
+                                   const LangOptions &LangOpts,
+                                   const NoBuiltinAttr *NBA = nullptr) {
+  auto AddNoBuiltinAttr = [&FuncAttrs](StringRef BuiltinName) {
+    SmallString<32> AttributeName;
+    AttributeName += "no-builtin-";
+    AttributeName += BuiltinName;
+    FuncAttrs.addAttribute(AttributeName);
+  };
+
+  // First, handle the language options passed through -fno-builtin[-<name>]
+  if (LangOpts.NoBuiltin) {
+    // -fno-builtin disables them all.
+    FuncAttrs.addAttribute("no-builtins");
+    return;
+  }
+
+  // Then, add attributes for builtins specified through -fno-builtin-<name>.
+  llvm::for_each(LangOpts.NoBuiltinFuncs, AddNoBuiltinAttr);
+
+  // Now, let's check the __attribute__((no_builtin("...")) attribute added to
+  // the source.
+  if (!NBA)
+    return;
+
+  // If there is a wildcard in the builtin names specified through the
+  // attribute, disable them all.
+  if (llvm::is_contained(NBA->builtinNames(), "*")) {
+    FuncAttrs.addAttribute("no-builtins");
+    return;
+  }
+
+  // And last, add the rest of the builtin names.
+  llvm::for_each(NBA->builtinNames(), AddNoBuiltinAttr);
+}
+
 void CodeGenModule::ConstructAttributeList(
     StringRef Name, const CGFunctionInfo &FI, CGCalleeInfo CalleeInfo,
     llvm::AttributeList &AttrList, unsigned &CallingConv, bool AttrOnCallSite) {
@@ -1850,6 +1886,8 @@ void CodeGenModule::ConstructAttributeList(
   const Decl *TargetDecl = CalleeInfo.getCalleeDecl().getDecl();
 
   bool HasOptnone = false;
+  // The NoBuiltinAttr attached to a TargetDecl (only allowed on FunctionDecls).
+  const NoBuiltinAttr *NBA = nullptr;
   // FIXME: handle sseregparm someday...
   if (TargetDecl) {
     if (TargetDecl->hasAttr<ReturnsTwiceAttr>())
@@ -1875,22 +1913,7 @@ void CodeGenModule::ConstructAttributeList(
       if (!(AttrOnCallSite && IsVirtualCall)) {
         if (Fn->isNoReturn())
           FuncAttrs.addAttribute(llvm::Attribute::NoReturn);
-
-        const auto *NBA = Fn->getAttr<NoBuiltinAttr>();
-        bool HasWildcard = NBA && llvm::is_contained(NBA->builtinNames(), "*");
-        if (getLangOpts().NoBuiltin || HasWildcard)
-          FuncAttrs.addAttribute("no-builtins");
-        else {
-          auto AddNoBuiltinAttr = [&FuncAttrs](StringRef BuiltinName) {
-            SmallString<32> AttributeName;
-            AttributeName += "no-builtin-";
-            AttributeName += BuiltinName;
-            FuncAttrs.addAttribute(AttributeName);
-          };
-          llvm::for_each(getLangOpts().NoBuiltinFuncs, AddNoBuiltinAttr);
-          if (NBA)
-            llvm::for_each(NBA->builtinNames(), AddNoBuiltinAttr);
-        }
+        NBA = Fn->getAttr<NoBuiltinAttr>();
       }
     }
 
@@ -1925,6 +1948,14 @@ void CodeGenModule::ConstructAttributeList(
     }
   }
 
+  // Attach "no-builtins" attributes to:
+  // * call sites: both `nobuiltin` and "no-builtins" or "no-builtin-<name>".
+  // * definitions: "no-builtins" or "no-builtin-<name>" only.
+  // The attributes can come from:
+  // * LangOpts: -ffreestanding, -fno-builtin, -fno-builtin-<name>
+  // * FunctionDecl attributes: __attribute__((no_builtin(...)))
+  addNoBuiltinAttributes(FuncAttrs, getLangOpts(), NBA);
+
   ConstructDefaultFnAttrList(Name, HasOptnone, AttrOnCallSite, FuncAttrs);
 
   // This must run after constructing the default function attribute list

clang/test/CodeGenCXX/global-init.cpp

@@ -2,6 +2,8 @@
 // RUN: %clang_cc1 -triple=x86_64-apple-darwin10 -emit-llvm %s -o - |FileCheck -check-prefix CHECK-NOEXC %s
 // RUN: %clang_cc1 -triple=x86_64-apple-darwin10 -emit-llvm -mframe-pointer=non-leaf %s -o - \
 // RUN:   | FileCheck -check-prefix CHECK-FP %s
+// RUN: %clang_cc1 -triple=x86_64-apple-darwin10 -emit-llvm %s -o - -fno-builtin \
+// RUN:   | FileCheck -check-prefix CHECK-NOBUILTIN %s
 
 struct A {
   A();
@@ -202,9 +204,12 @@ namespace test7 {
 
 // rdar://problem/8090834: this should be nounwind
 // CHECK-NOEXC: define internal void @_GLOBAL__sub_I_global_init.cpp() [[NUW:#[0-9]+]] section "__TEXT,__StaticInit,regular,pure_instructions" {
-
 // CHECK-NOEXC: attributes [[NUW]] = { noinline nounwind{{.*}} }
 
+// Make sure we mark global initializers with the no-builtins attribute.
+// CHECK-NOBUILTIN: define internal void @_GLOBAL__sub_I_global_init.cpp() [[NUW:#[0-9]+]] section "__TEXT,__StaticInit,regular,pure_instructions" {
+// CHECK-NOBUILTIN: attributes [[NUW]] = { noinline nounwind{{.*}}"no-builtins"{{.*}} }
+
 // PR21811: attach the appropriate attribute to the global init function
 // CHECK-FP: define internal void @_GLOBAL__sub_I_global_init.cpp() [[NUX:#[0-9]+]] section "__TEXT,__StaticInit,regular,pure_instructions" {
 // CHECK-FP: attributes [[NUX]] = { noinline nounwind {{.*}}"frame-pointer"="non-leaf"{{.*}} }