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Convert shifts to muls to assist reassociation. This implements

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Reassociate/shifttest.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21761 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-05-07 04:24:13 +00:00
parent 5cc924ac42
commit 0975ed5f4e
1 changed files with 27 additions and 2 deletions
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29
lib/Transforms/Scalar/Reassociate.cpp
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@ -22,11 +22,11 @@
#define DEBUG_TYPE "reassociate"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
#include "llvm/Pass.h"
#include "llvm/Constant.h"
#include "llvm/Type.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/PostOrderIterator.h"
@ -243,6 +243,25 @@ static Instruction *BreakUpSubtract(Instruction *Sub) {
return New;
}
/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
/// by one, change this into a multiply by a constant to assist with further
/// reassociation.
static Instruction *ConvertShiftToMul(Instruction *Shl) {
if (!isReassociableOp(Shl->getOperand(0), Instruction::Mul) &&
!(Shl->hasOneUse() && isReassociableOp(Shl->use_back(),Instruction::Mul)))
return 0;
Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
std::string Name = Shl->getName(); Shl->setName("");
Instruction *Mul = BinaryOperator::createMul(Shl->getOperand(0), MulCst,
Name, Shl);
Shl->replaceAllUsesWith(Mul);
Shl->eraseFromParent();
return Mul;
}
/// ReassociateBB - Inspect all of the instructions in this basic block,
/// reassociating them as we go.
@ -256,6 +275,12 @@ bool Reassociate::ReassociateBB(BasicBlock *BB) {
Changed = true;
BI = NI;
}
if (BI->getOpcode() == Instruction::Shl &&
isa<ConstantInt>(BI->getOperand(1)))
if (Instruction *NI = ConvertShiftToMul(BI)) {
Changed = true;
BI = NI;
}
// If this instruction is a commutative binary operator, and the ranks of
// the two operands are sorted incorrectly, fix it now.