bool ScopDetection::isInvariant(const Value &Val, const Region &Reg) const {
// A reference to function argument or constant value is invariant.
if (isa<Argument>(Val) || isa<Constant>(Val))
return true;
const Instruction *I = dyn_cast<Instruction>(&Val);
if (!I)
return false;
if (!Reg.contains(I))
return true;
if (I->mayHaveSideEffects())
return false;
// When Val is a Phi node, it is likely not invariant. We do not check whether
// Phi nodes are actually invariant, we assume that Phi nodes are usually not
// invariant. Recursively checking the operators of Phi nodes would lead to
// infinite recursion.
if (isa<PHINode>(*I))
return false;
for (const Use &Operand : I->operands())
if (!isInvariant(*Operand, Reg))
return false;
// When the instruction is a load instruction, check that no write to memory
// in the region aliases with the load.
if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
AliasAnalysis::Location Loc = AA->getLocation(LI);
const Region::const_block_iterator BE = Reg.block_end();
// Check if any basic block in the region can modify the location pointed to
// by 'Loc'. If so, 'Val' is (likely) not invariant in the region.
for (const BasicBlock *BB : Reg.blocks())
if (AA->canBasicBlockModify(*BB, Loc))
return false;
}
return true;
}
