[ValueTracking] Look through casts when determining non-nullness
Bitcast and certain Ptr2Int/Int2Ptr instructions will not alter the
value of their operand and can therefore be looked through when we
determine non-nullness.
Differential Revision: https://reviews.llvm.org/D54956
llvm-svn: 352293
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 0aaabec..06b0bd7 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2036,11 +2036,33 @@
if (isKnownNonNullFromDominatingCondition(V, Q.CxtI, Q.DT))
return true;
+ // Look through bitcast operations, GEPs, and int2ptr instructions as they
+ // do not alter the value, or at least not the nullness property of the
+ // value, e.g., int2ptr is allowed to zero/sign extend the value.
+ //
+ // Note that we have to take special care to avoid looking through
+ // truncating casts, e.g., int2ptr/ptr2int with appropriate sizes, as well
+ // as casts that can alter the value, e.g., AddrSpaceCasts.
if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V))
if (isGEPKnownNonNull(GEP, Depth, Q))
return true;
+
+ if (auto *BCO = dyn_cast<BitCastOperator>(V))
+ return isKnownNonZero(BCO->getOperand(0), Depth, Q);
+
+ if (auto *I2P = dyn_cast<IntToPtrInst>(V))
+ if (Q.DL.getTypeSizeInBits(I2P->getSrcTy()) <=
+ Q.DL.getTypeSizeInBits(I2P->getDestTy()))
+ return isKnownNonZero(I2P->getOperand(0), Depth, Q);
}
+ // Similar to int2ptr above, we can look through ptr2int here if the cast
+ // is a no-op or an extend and not a truncate.
+ if (auto *P2I = dyn_cast<PtrToIntInst>(V))
+ if (Q.DL.getTypeSizeInBits(P2I->getSrcTy()) <=
+ Q.DL.getTypeSizeInBits(P2I->getDestTy()))
+ return isKnownNonZero(P2I->getOperand(0), Depth, Q);
+
unsigned BitWidth = getBitWidth(V->getType()->getScalarType(), Q.DL);
// X | Y != 0 if X != 0 or Y != 0.