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[SCCP] add helper function for replacing signed operations; NFC 

Preliminary refactoring for planned enhancement in D133198.
This commit is contained in:
Sanjay Patel 2022-09-03 10:12:13 -04:00
parent bddbd408b7
commit 22e1f66f26
1 changed files with 38 additions and 17 deletions
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55
llvm/lib/Transforms/Scalar/SCCP.cpp
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@ -154,6 +154,41 @@ static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) {
return true;
}
/// Try to replace signed instructions with their unsigned equivalent.
static bool replaceSignedInst(SCCPSolver &Solver,
SmallPtrSetImpl<Value *> &InsertedValues,
Instruction &Inst) {
// Determine if a signed value is known to be >= 0.
auto isNonNegative = [&Solver](Value *V) {
const ValueLatticeElement &IV = Solver.getLatticeValueFor(V);
return IV.isConstantRange(/*UndefAllowed=*/false) &&
IV.getConstantRange().isAllNonNegative();
};
Instruction *NewInst = nullptr;
switch (Inst.getOpcode()) {
case Instruction::SExt: {
// If the source value is not negative, this is a zext.
Value *Op0 = Inst.getOperand(0);
if (isa<Constant>(Op0) || InsertedValues.count(Op0) || !isNonNegative(Op0))
return false;
NewInst = new ZExtInst(Op0, Inst.getType(), "", &Inst);
break;
}
default:
return false;
}
// Wire up the new instruction and update state.
assert(NewInst && "Expected replacement instruction");
NewInst->takeName(&Inst);
InsertedValues.insert(NewInst);
Inst.replaceAllUsesWith(NewInst);
Solver.removeLatticeValueFor(&Inst);
Inst.eraseFromParent();
return true;
}
static bool simplifyInstsInBlock(SCCPSolver &Solver, BasicBlock &BB,
SmallPtrSetImpl<Value *> &InsertedValues,
Statistic &InstRemovedStat,
@ -168,23 +203,9 @@ static bool simplifyInstsInBlock(SCCPSolver &Solver, BasicBlock &BB,
MadeChanges = true;
++InstRemovedStat;
} else if (isa<SExtInst>(&Inst)) {
Value *ExtOp = Inst.getOperand(0);
if (isa<Constant>(ExtOp) || InsertedValues.count(ExtOp))
continue;
const ValueLatticeElement &IV = Solver.getLatticeValueFor(ExtOp);
if (!IV.isConstantRange(/*UndefAllowed=*/false))
continue;
if (IV.getConstantRange().isAllNonNegative()) {
auto *ZExt = new ZExtInst(ExtOp, Inst.getType(), "", &Inst);
ZExt->takeName(&Inst);
InsertedValues.insert(ZExt);
Inst.replaceAllUsesWith(ZExt);
Solver.removeLatticeValueFor(&Inst);
Inst.eraseFromParent();
InstReplacedStat++;
MadeChanges = true;
}
} else if (replaceSignedInst(Solver, InsertedValues, Inst)) {
MadeChanges = true;
++InstReplacedStat;
}
}
return MadeChanges;