From 029c5c7fdb07366d14577f789e43498f49a4450d Mon Sep 17 00:00:00 2001 From: Nadav Rotem Date: Tue, 3 Mar 2015 21:39:02 +0000 Subject: Teach ComputeNumSignBits about signed divisions. http://reviews.llvm.org/D8028 rdar://20023136 llvm-svn: 231140 --- llvm/lib/Analysis/ValueTracking.cpp | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'llvm/lib/Analysis/ValueTracking.cpp') diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index 0458d284eb4..d5202664ae5 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -1723,6 +1723,23 @@ unsigned ComputeNumSignBits(Value *V, const DataLayout *TD, Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits(); return ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q) + Tmp; + case Instruction::SDiv: + const APInt *Denominator; + // sdiv X, C -> adds log(C) sign bits. + if (match(U->getOperand(1), m_APInt(Denominator))) { + + // Ignore non-positive denominator. + if (!Denominator->isStrictlyPositive()) + break; + + // Calculate the incoming numerator bits. + unsigned NumBits = ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q); + + // Add floor(log(C)) bits to the numerator bits. + return std::min(TyBits, NumBits + Denominator->logBase2()); + } + break; + case Instruction::AShr: { Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q); // ashr X, C -> adds C sign bits. Vectors too. -- cgit v1.2.3