[PATCH] D67658: Revert "[SLC] Preserve attrs for strncpy(x, "", y) -> memset(align 1 x, '\0', y)"

[Dávid Bolvanský via Phabricator via llvm-commits]

xbolva00 added a comment.

In D67658#1672604 <https://reviews.llvm.org/D67658#1672604>, @lebedev.ri wrote:

> There was several commits touching this code in rapid succession.
>  This seems to revert rL372101 <https://reviews.llvm.org/rL372101>, but what about rL372097 <https://reviews.llvm.org/rL372097>, rL372096 <https://reviews.llvm.org/rL372096>, and possibly relevant part of D53342 <https://reviews.llvm.org/D53342>/rL372091 <https://reviews.llvm.org/rL372091> ?


Yeah, but unfortunely. My system GCC 7 does not warn me about that "attrs" bug :/ (testing compiler. fix currently).

The failed test mentions strncat so yeah, maybe this revert is incorrect - but let's just do it to see.

I checked the new code for strncat again and I see nothing bad.

  annotateNonNullBasedOnAccess(CI, 0);
   if (isKnownNonZero(Size, DL))
     annotateNonNullBasedOnAccess(CI, 1);
  
   // We don't do anything if length is not constant.
   ConstantInt *LengthArg = dyn_cast<ConstantInt>(Size);
   if (LengthArg) {
     Len = LengthArg->getZExtValue();
     // strncat(x, c, 0) -> x
     if (!Len)
       return Dst;
   } else {
     return nullptr;
   }

so for "strncat(to - 1, from, 0)" we eliminate strncat call and return "to - 1" ptr. (patch does not change the behaviour here).


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D67658/new/

https://reviews.llvm.org/D67658