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Now that all the code generators support the select instruction, and the instcombine

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pass can eliminate many nasty cases of them, start generating them in the optimizers

llvm-svn: 12545
This commit is contained in:
Chris Lattner 2004-03-30 19:44:05 +00:00
parent b6612acb18
commit 145aea5c4c
1 changed files with 9 additions and 78 deletions
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87
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -852,84 +852,15 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
Value *FalseVal =
PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
// FIXME: when we have a 'select' statement, we can be completely
// generic and clean here and let the instcombine pass clean up
// after us, by folding the select instructions away when possible.
//
if (TrueVal == FalseVal) {
// Degenerate case...
PN->replaceAllUsesWith(TrueVal);
BB->getInstList().erase(PN);
Changed = true;
} else if (isa<ConstantBool>(TrueVal) &&
isa<ConstantBool>(FalseVal)) {
if (TrueVal == ConstantBool::True) {
// The PHI node produces the same thing as the condition.
PN->replaceAllUsesWith(IfCond);
} else {
// The PHI node produces the inverse of the condition. Insert a
// "NOT" instruction, which is really a XOR.
Value *InverseCond =
BinaryOperator::createNot(IfCond, IfCond->getName()+".inv",
AfterPHIIt);
PN->replaceAllUsesWith(InverseCond);
}
BB->getInstList().erase(PN);
Changed = true;
} else if (isa<ConstantInt>(TrueVal) && isa<ConstantInt>(FalseVal)){
// If this is a PHI of two constant integers, we insert a cast of
// the boolean to the integer type in question, giving us 0 or 1.
// Then we multiply this by the difference of the two constants,
// giving us 0 if false, and the difference if true. We add this
// result to the base constant, giving us our final value. We
// rely on the instruction combiner to eliminate many special
// cases, like turning multiplies into shifts when possible.
std::string Name = PN->getName(); PN->setName("");
Value *TheCast = new CastInst(IfCond, TrueVal->getType(),
Name, AfterPHIIt);
Constant *TheDiff = ConstantExpr::get(Instruction::Sub,
cast<Constant>(TrueVal),
cast<Constant>(FalseVal));
Value *V = TheCast;
if (TheDiff != ConstantInt::get(TrueVal->getType(), 1))
V = BinaryOperator::create(Instruction::Mul, TheCast,
TheDiff, TheCast->getName()+".scale",
AfterPHIIt);
if (!cast<Constant>(FalseVal)->isNullValue())
V = BinaryOperator::create(Instruction::Add, V, FalseVal,
V->getName()+".offs", AfterPHIIt);
PN->replaceAllUsesWith(V);
BB->getInstList().erase(PN);
Changed = true;
} else if (isa<ConstantInt>(FalseVal) &&
cast<Constant>(FalseVal)->isNullValue()) {
// If the false condition is an integral zero value, we can
// compute the PHI by multiplying the condition by the other
// value.
std::string Name = PN->getName(); PN->setName("");
Value *TheCast = new CastInst(IfCond, TrueVal->getType(),
Name+".c", AfterPHIIt);
Value *V = BinaryOperator::create(Instruction::Mul, TrueVal,
TheCast, Name, AfterPHIIt);
PN->replaceAllUsesWith(V);
BB->getInstList().erase(PN);
Changed = true;
} else if (isa<ConstantInt>(TrueVal) &&
cast<Constant>(TrueVal)->isNullValue()) {
// If the true condition is an integral zero value, we can compute
// the PHI by multiplying the inverse condition by the other
// value.
std::string Name = PN->getName(); PN->setName("");
Value *NotCond = BinaryOperator::createNot(IfCond, Name+".inv",
AfterPHIIt);
Value *TheCast = new CastInst(NotCond, TrueVal->getType(),
Name+".inv", AfterPHIIt);
Value *V = BinaryOperator::create(Instruction::Mul, FalseVal,
TheCast, Name, AfterPHIIt);
PN->replaceAllUsesWith(V);
BB->getInstList().erase(PN);
Changed = true;
}
// Change the PHI node into a select instruction.
BasicBlock::iterator InsertPos = PN;
while (isa<PHINode>(InsertPos)) ++InsertPos;
std::string Name = PN->getName(); PN->setName("");
PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal,
Name, InsertPos));
BB->getInstList().erase(PN);
Changed = true;
}
}
}