diff options
Diffstat (limited to 'lib/Analysis/ValueTracking.cpp')
| -rw-r--r-- | lib/Analysis/ValueTracking.cpp | 29 |
1 files changed, 27 insertions, 2 deletions
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp index c4f6faf612..3c21e2039c 100644 --- a/lib/Analysis/ValueTracking.cpp +++ b/lib/Analysis/ValueTracking.cpp @@ -48,8 +48,9 @@ static unsigned getOpcode(const Value *V) { void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero, APInt &KnownOne, TargetData *TD, unsigned Depth) { + const unsigned MaxDepth = 6; assert(V && "No Value?"); - assert(Depth <= 6 && "Limit Search Depth"); + assert(Depth <= MaxDepth && "Limit Search Depth"); unsigned BitWidth = Mask.getBitWidth(); assert((V->getType()->isInteger() || isa<PointerType>(V->getType())) && "Not integer or pointer type!"); @@ -88,7 +89,7 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, KnownZero.clear(); KnownOne.clear(); // Start out not knowing anything. - if (Depth == 6 || Mask == 0) + if (Depth == MaxDepth || Mask == 0) return; // Limit search depth. User *I = dyn_cast<User>(V); @@ -522,6 +523,30 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, } } } + + // Otherwise take the unions of the known bit sets of the operands, + // taking conservative care to avoid excessive recursion. + if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) { + KnownZero = APInt::getAllOnesValue(BitWidth); + KnownOne = APInt::getAllOnesValue(BitWidth); + for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) { + // Skip direct self references. + if (P->getIncomingValue(i) == P) continue; + + KnownZero2 = APInt(BitWidth, 0); + KnownOne2 = APInt(BitWidth, 0); + // Recurse, but cap the recursion to one level, because we don't + // want to waste time spinning around in loops. + ComputeMaskedBits(P->getIncomingValue(i), KnownZero | KnownOne, + KnownZero2, KnownOne2, TD, MaxDepth-1); + KnownZero &= KnownZero2; + KnownOne &= KnownOne2; + // If all bits have been ruled out, there's no need to check + // more operands. + if (!KnownZero && !KnownOne) + break; + } + } break; } case Instruction::Call: |