[llvm-commits] [PATCH] Add support to ValueTracking for determining that a pointer is non-null by virtue of inbounds GEPs that preclude a null pointer.

[Duncan Sands]

Hi Chandler,

 > --- lib/Analysis/ValueTracking.cpp
> +++ lib/Analysis/ValueTracking.cpp
> @@ -885,26 +890,28 @@
>     // inherently violate the inbounds contract within address space zero.
>     for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP);
>          GTI != GTE; ++GTI) {
> -    ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
> -    if (!OpC && Depth >= MaxDepth)
> -      return false;
> -
> -    // If we have a non-zero constant or a known-non-zero value, we can try to
> -    // reason about the GEP.
> -    if ((!OpC && !isKnownNonZero(GTI.getOperand(), DL, Depth++)) ||
> -        (OpC && OpC->isZero()))
> -      continue;
> -
> +    // Struct types are easy -- they must always be indexed by a constant.
>       if (StructType *STy = dyn_cast<StructType>(*GTI)) {
> -      assert(OpC && "Only constants can index a struct!");
> +      ConstantInt *OpC = cast<ConstantInt>(GTI.getOperand());
>         unsigned ElementIdx = OpC->getZExtValue();
>         const StructLayout *SL = DL->getStructLayout(STy);
>         uint64_t ElementOffset = SL->getElementOffset(ElementIdx);
>         if (ElementOffset > 0)
>           return true;
> -    } else if (DL->getTypeAllocSize(GTI.getIndexedType()) > 0) {
> -      return true;
> +      continue;
>       }
> +
> +    // If we have a zero-sized type, the index doesn't matter. Keep looing.

looing -> looking.

Otherwise looks great to me.  Thanks for making the changes!

Ciao, Duncan.