SILValue BBState::computeForwardingValues(RLEContext &Ctx, MemLocation &L,
SILInstruction *InsertPt,
bool UseForwardValOut) {
SILBasicBlock *ParentBB = InsertPt->getParent();
bool IsTerminator = (InsertPt == ParentBB->getTerminator());
// We do not have a SILValue for the current MemLocation, try to construct
// one.
//
// Collect the locations and their corresponding values into a map.
// First, collect current available locations and their corresponding values
// into a map.
MemLocationValueMap Values;
if (!Ctx.gatherValues(ParentBB, L, Values, UseForwardValOut))
return SILValue();
// If the InsertPt is the terminator instruction of the basic block, we
// *refresh* it as terminator instruction could be deleted as a result
// of adding new edge values to the terminator instruction.
if (IsTerminator)
InsertPt = ParentBB->getTerminator();
// Second, reduce the available values into a single SILValue we can use to
// forward.
SILValue TheForwardingValue;
TheForwardingValue = MemLocation::reduceWithValues(L, &ParentBB->getModule(),
Values, InsertPt);
/// Return the forwarding value.
return TheForwardingValue;
}
bool BBState::setupRLE(RLEContext &Ctx, SILInstruction *I, SILValue Mem) {
// Try to construct a SILValue for the current MemLocation.
//
// Collect the locations and their corresponding values into a map.
MemLocation L(Mem);
MemLocationValueMap Values;
if (!Ctx.gatherValues(I->getParent(), L, Values, false))
return false;
// Reduce the available values into a single SILValue we can use to forward.
SILModule *Mod = &I->getModule();
SILValue TheForwardingValue;
TheForwardingValue = MemLocation::reduceWithValues(L, Mod, Values, I);
if (!TheForwardingValue)
return false;
// Now we have the forwarding value, record it for forwarding!.
//
// NOTE: we do not perform the RLE right here because doing so could introduce
// new MemLocations.
//
// e.g.
// %0 = load %x
// %1 = load %x
// %2 = extract_struct %1, #a
// %3 = load %2
//
// If we perform the RLE and replace %1 with %0, we end up having a memory
// location we do not have before, i.e. Base == %0, and Path == #a.
//
// We may be able to add the MemLocation to the vault, but it gets
// complicated very quickly, e.g. we need to resize the bit vectors size,
// etc.
//
// However, since we already know the instruction to replace and the value to
// replace it with, we can record it for now and forwarded it after all the
// forwardable values are recorded in the function.
//
RedundantLoads[I] = TheForwardingValue;
return true;
}