/// This returns true if the two MIs need a chain edge betwee them.
/// If these are not even memory operations, we still may need
/// chain deps between them. The question really is - could
/// these two MIs be reordered during scheduling from memory dependency
/// point of view.
static bool MIsNeedChainEdge(AliasAnalysis *AA, const MachineFrameInfo *MFI,
MachineInstr *MIa,
MachineInstr *MIb) {
// Cover a trivial case - no edge is need to itself.
if (MIa == MIb)
return false;
if (isUnsafeMemoryObject(MIa, MFI) || isUnsafeMemoryObject(MIb, MFI))
return true;
// If we are dealing with two "normal" loads, we do not need an edge
// between them - they could be reordered.
if (!MIa->mayStore() && !MIb->mayStore())
return false;
// To this point analysis is generic. From here on we do need AA.
if (!AA)
return true;
MachineMemOperand *MMOa = *MIa->memoperands_begin();
MachineMemOperand *MMOb = *MIb->memoperands_begin();
// FIXME: Need to handle multiple memory operands to support all targets.
if (!MIa->hasOneMemOperand() || !MIb->hasOneMemOperand())
llvm_unreachable("Multiple memory operands.");
// The following interface to AA is fashioned after DAGCombiner::isAlias
// and operates with MachineMemOperand offset with some important
// assumptions:
// - LLVM fundamentally assumes flat address spaces.
// - MachineOperand offset can *only* result from legalization and
// cannot affect queries other than the trivial case of overlap
// checking.
// - These offsets never wrap and never step outside
// of allocated objects.
// - There should never be any negative offsets here.
//
// FIXME: Modify API to hide this math from "user"
// FIXME: Even before we go to AA we can reason locally about some
// memory objects. It can save compile time, and possibly catch some
// corner cases not currently covered.
assert ((MMOa->getOffset() >= 0) && "Negative MachineMemOperand offset");
assert ((MMOb->getOffset() >= 0) && "Negative MachineMemOperand offset");
int64_t MinOffset = std::min(MMOa->getOffset(), MMOb->getOffset());
int64_t Overlapa = MMOa->getSize() + MMOa->getOffset() - MinOffset;
int64_t Overlapb = MMOb->getSize() + MMOb->getOffset() - MinOffset;
AliasAnalysis::AliasResult AAResult = AA->alias(
AliasAnalysis::Location(MMOa->getValue(), Overlapa,
MMOa->getTBAAInfo()),
AliasAnalysis::Location(MMOb->getValue(), Overlapb,
MMOb->getTBAAInfo()));
return (AAResult != AliasAnalysis::NoAlias);
}
