[PATCH] D117600: [CGCall] Annotate operator new with inaccessiblememonly if AssumeSaneOperatorNew is on

[Bryce Wilson via Phabricator via cfe-commits]

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- Add change to docs


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 <https://reviews.llvm.org/D117180>) allowing operator new to be correct when needed without causing the significant regression that we found when removing the special case).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D117600

Files:
  clang/include/clang/Driver/Options.td
  clang/lib/CodeGen/CGCall.cpp


Index: clang/lib/CodeGen/CGCall.cpp
===================================================================
--- clang/lib/CodeGen/CGCall.cpp
+++ clang/lib/CodeGen/CGCall.cpp
@@ -2062,11 +2062,14 @@
       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("inaccessiblememonly");
+        }
       }
       const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Fn);
       const bool IsVirtualCall = MD && MD->isVirtual();
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -2256,7 +2256,7 @@
 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">;


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