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Teach ScalarEvolution how to recognize zext-inreg and sext-inreg, 

as they appear in LLVM IR. This isn't particularly interesting
on its own; this is just setting up some infrastructure.

llvm-svn: 69655
This commit is contained in:
Dan Gohman 2009-04-21 02:26:00 +00:00
parent 6f2878360c
commit 0ec0537403
1 changed files with 27 additions and 0 deletions
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27
llvm/lib/Analysis/ScalarEvolution.cpp
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@ -1947,6 +1947,19 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
case Instruction::Sub:
return SE.getMinusSCEV(getSCEV(U->getOperand(0)),
getSCEV(U->getOperand(1)));
case Instruction::And:
// For an expression like x&255 that merely masks off the high bits,
// use zext(trunc(x)) as the SCEV expression.
if (ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1))) {
const APInt &A = CI->getValue();
unsigned Ones = A.countTrailingOnes();
if (APIntOps::isMask(Ones, A))
return
SE.getZeroExtendExpr(SE.getTruncateExpr(getSCEV(U->getOperand(0)),
IntegerType::get(Ones)),
U->getType());
}
break;
case Instruction::Or:
// If the RHS of the Or is a constant, we may have something like:
// X*4+1 which got turned into X*4|1. Handle this as an Add so loop
@ -1996,6 +2009,20 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
}
break;
case Instruction::AShr:
// For a two-shift sext-inreg, use sext(trunc(x)) as the SCEV expression.
if (ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1)))
if (Instruction *L = dyn_cast<Instruction>(U->getOperand(0)))
if (L->getOpcode() == Instruction::Shl &&
L->getOperand(1) == U->getOperand(1)) {
uint64_t Amt = CI->getZExtValue();
return
SE.getSignExtendExpr(SE.getTruncateExpr(getSCEV(L->getOperand(0)),
IntegerType::get(Amt)),
U->getType());
}
break;
case Instruction::Trunc:
return SE.getTruncateExpr(getSCEV(U->getOperand(0)), U->getType());