[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.
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http://llvm-reviews.chandlerc.com/D160