From 6b79e2d2027bb05dbeeb6789e12268c0b71bc78d Mon Sep 17 00:00:00 2001 From: Reid Spencer Date: Mon, 12 Mar 2007 17:15:10 +0000 Subject: [PATCH] Add an APInt version of ShrinkDemandedConstant. Patch by Zhou Sheng. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35063 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../Scalar/InstructionCombining.cpp | 24 +++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 62a7a8dea4d..d2c549c2881 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -1004,6 +1004,30 @@ static bool ShrinkDemandedConstant(Instruction *I, unsigned OpNo, return true; } +/// ShrinkDemandedConstant - Check to see if the specified operand of the +/// specified instruction is a constant integer. If so, check to see if there +/// are any bits set in the constant that are not demanded. If so, shrink the +/// constant and return true. +static bool ShrinkDemandedConstant(Instruction *I, unsigned OpNo, + APInt Demanded) { + assert(I && "No instruction?"); + assert(OpNo < I->getNumOperands() && "Operand index too large"); + + // If the operand is not a constant integer, nothing to do. + ConstantInt *OpC = dyn_cast(I->getOperand(OpNo)); + if (!OpC) return false; + + // If there are no bits set that aren't demanded, nothing to do. + Demanded.zextOrTrunc(OpC->getValue().getBitWidth()); + if ((~Demanded & OpC->getValue()) == 0) + return false; + + // This instruction is producing bits that are not demanded. Shrink the RHS. + Demanded &= OpC->getValue(); + I->setOperand(OpNo, ConstantInt::get(Demanded)); + return true; +} + // ComputeSignedMinMaxValuesFromKnownBits - Given a signed integer type and a // set of known zero and one bits, compute the maximum and minimum values that // could have the specified known zero and known one bits, returning them in