[CGCall] Annotate operator new with inaccessiblememonly if AssumeSaneOperatorNew is on

[Bryce-MW]

Summary

Basic Alias Analysis in LLVM currently has a special case for allocation functions (including operator new) that essentially assumes that they are inaccessiblememonly. Operator new is not currently annotated with inaccessiblememonly because that is not technically correct (especially considering global replacement functions). This patch allows that case to be removed (D117180) allowing operator new to be correct when needed without causing the significant regression that we found when removing the special case).

[Bryce-MW]

• Add change to docs

[nikic]

clang/lib/CodeGen/CGCall.cpp

2071

This should be Attribute::InacccessibleMemOnly. It's not a string attribute.

[Bryce-MW]

• Use proper attribute

clang/lib/CodeGen/CGCall.cpp

2071

Thanks, I tried to look for a list but I didn't have any luck (and my IDE was having trouble loading the CMake project so I couldn't jump to definition on another attribute).

[xbolva00]

Test?

clang/include/clang/Driver/Options.td

 
 def fmudflapth : Flag<["-"], "fmudflapth">, Group<f_Group>;
 def fmudflap : Flag<["-"], "fmudflap">, Group<f_Group>;
 def fnested_functions : Flag<["-"], "fnested-functions">, Group<f_Group>;
 def fnext_runtime : Flag<["-"], "fnext-runtime">, Group<f_Group>;
 def fno_asm : Flag<["-"], "fno-asm">, Group<f_Group>;
 def fno_asynchronous_unwind_tables : Flag<["-"], "fno-asynchronous-unwind-tables">, Group<f_Group>;
 def fno_assume_sane_operator_new : Flag<["-"], "fno-assume-sane-operator-new">, Group<f_Group>,
-  HelpText<"Don't assume that C++'s global operator new can't alias any pointer">,
+  HelpText<"Don't assume that C++'s global operator new can't alias any pointer or access accessible memory">,
   Flags<[CC1Option]>, MarshallingInfoNegativeFlag<CodeGenOpts<"AssumeSaneOperatorNew">>;
 def fno_builtin : Flag<["-"], "fno-builtin">, Group<f_Group>, Flags<[CC1Option, CoreOption]>,
   HelpText<"Disable implicit builtin knowledge of functions">;
 def fno_builtin_ : Joined<["-"], "fno-builtin-">, Group<f_Group>, Flags<[CC1Option, CoreOption]>,
   HelpText<"Disable implicit builtin knowledge of a specific function">;
 def fno_diagnostics_color : Flag<["-"], "fno-diagnostics-color">, Group<f_Group>,
   Flags<[CoreOption, NoXarchOption]>;
 def fno_common : Flag<["-"], "fno-common">, Group<f_Group>, Flags<[CC1Option]>,

clang/lib/CodeGen/CGCall.cpp

if (TargetDecl->hasAttr<NoDuplicateAttr>())
       FuncAttrs.addAttribute(llvm::Attribute::NoDuplicate);
     if (TargetDecl->hasAttr<ConvergentAttr>())
       FuncAttrs.addAttribute(llvm::Attribute::Convergent);
 
     if (const FunctionDecl *Fn = dyn_cast<FunctionDecl>(TargetDecl)) {
       AddAttributesFromFunctionProtoType(
           getContext(), FuncAttrs, Fn->getType()->getAs<FunctionProtoType>());
       if (AttrOnCallSite && Fn->isReplaceableGlobalAllocationFunction()) {
-        // A sane operator new returns a non-aliasing pointer.
+        // A sane operator new returns a non-aliasing pointer and is
+        // inaccessiblememonly
         auto Kind = Fn->getDeclName().getCXXOverloadedOperator();
         if (getCodeGenOpts().AssumeSaneOperatorNew &&
-            (Kind == OO_New || Kind == OO_Array_New))
+            (Kind == OO_New || Kind == OO_Array_New)) {
           RetAttrs.addAttribute(llvm::Attribute::NoAlias);
+          FuncAttrs.addAttribute(llvm::Attribute::InacccessibleMemOnly);
+        }
       }
       const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Fn);
       const bool IsVirtualCall = MD && MD->isVirtual();
       // Don't use [[noreturn]], _Noreturn or [[no_builtin]] for a call to a
       // virtual function. These attributes are not inherited by overloads.
       if (!(AttrOnCallSite && IsVirtualCall)) {
         if (Fn->isNoReturn())
           FuncAttrs.addAttribute(llvm::Attribute::NoReturn);