From d30f308a9ff949cb868df5a5e731a3a912c522b7 Mon Sep 17 00:00:00 2001 From: Bjorn Pettersson Date: Thu, 28 Feb 2019 15:45:29 +0000 Subject: Add support for computing "zext of value" in KnownBits. NFCI Summary: The description of KnownBits::zext() and KnownBits::zextOrTrunc() has confusingly been telling that the operation is equivalent to zero extending the value we're tracking. That has not been true, instead the user has been forced to explicitly set the extended bits as known zero afterwards. This patch adds a second argument to KnownBits::zext() and KnownBits::zextOrTrunc() to control if the extended bits should be considered as known zero or as unknown. Reviewers: craig.topper, RKSimon Reviewed By: RKSimon Subscribers: javed.absar, hiraditya, jdoerfert, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D58650 llvm-svn: 355099 --- llvm/lib/Analysis/ValueTracking.cpp | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) (limited to 'llvm/lib/Analysis/ValueTracking.cpp') diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index 80a08e2fdd0..f6e3886f652 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -1128,12 +1128,9 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known, Q.DL.getTypeSizeInBits(ScalarTy); assert(SrcBitWidth && "SrcBitWidth can't be zero"); - Known = Known.zextOrTrunc(SrcBitWidth); + Known = Known.zextOrTrunc(SrcBitWidth, false); computeKnownBits(I->getOperand(0), Known, Depth + 1, Q); - Known = Known.zextOrTrunc(BitWidth); - // Any top bits are known to be zero. - if (BitWidth > SrcBitWidth) - Known.Zero.setBitsFrom(SrcBitWidth); + Known = Known.zextOrTrunc(BitWidth, true /* ExtendedBitsAreKnownZero */); break; } case Instruction::BitCast: { -- cgit v1.2.3