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Convert shifts to muls to assist reassociation. This implements
Reassociate/shifttest.ll git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21761 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -22,11 +22,11 @@
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#define DEBUG_TYPE "reassociate"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Type.h"
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#include "llvm/Pass.h"
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#include "llvm/Constant.h"
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#include "llvm/Type.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/PostOrderIterator.h"
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@ -243,6 +243,25 @@ static Instruction *BreakUpSubtract(Instruction *Sub) {
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return New;
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}
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/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
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/// by one, change this into a multiply by a constant to assist with further
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/// reassociation.
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static Instruction *ConvertShiftToMul(Instruction *Shl) {
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if (!isReassociableOp(Shl->getOperand(0), Instruction::Mul) &&
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!(Shl->hasOneUse() && isReassociableOp(Shl->use_back(),Instruction::Mul)))
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return 0;
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Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
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MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
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std::string Name = Shl->getName(); Shl->setName("");
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Instruction *Mul = BinaryOperator::createMul(Shl->getOperand(0), MulCst,
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Name, Shl);
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Shl->replaceAllUsesWith(Mul);
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Shl->eraseFromParent();
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return Mul;
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}
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/// ReassociateBB - Inspect all of the instructions in this basic block,
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/// reassociating them as we go.
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@ -256,6 +275,12 @@ bool Reassociate::ReassociateBB(BasicBlock *BB) {
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Changed = true;
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BI = NI;
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}
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if (BI->getOpcode() == Instruction::Shl &&
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isa<ConstantInt>(BI->getOperand(1)))
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if (Instruction *NI = ConvertShiftToMul(BI)) {
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Changed = true;
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BI = NI;
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}
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// If this instruction is a commutative binary operator, and the ranks of
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// the two operands are sorted incorrectly, fix it now.
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