+/// \brief Compute the value of Val on the edge BBFrom -> BBTo, or the value at
+/// the basic block if the edge does not constraint Val.
+bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
+ BasicBlock *BBTo, LVILatticeVal &Result) {
+ // If already a constant, there is nothing to compute.
+ if (Constant *VC = dyn_cast<Constant>(Val)) {
+ Result = LVILatticeVal::get(VC);
+ return true;
+ }
+
+ if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
+ if (!Result.isConstantRange() ||
+ Result.getConstantRange().getSingleElement())
+ return true;
+
+ // FIXME: this check should be moved to the beginning of the function when
+ // LVI better supports recursive values. Even for the single value case, we
+ // can intersect to detect dead code (an empty range).
+ if (!hasBlockValue(Val, BBFrom)) {
+ BlockValueStack.push(std::make_pair(BBFrom, Val));
+ return false;
+ }
+
+ // Try to intersect ranges of the BB and the constraint on the edge.
+ LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
+ if (!InBlock.isConstantRange())
+ return true;
+
+ ConstantRange Range =
+ Result.getConstantRange().intersectWith(InBlock.getConstantRange());
+ Result = LVILatticeVal::getRange(Range);
+ return true;
+ }
+
+ if (!hasBlockValue(Val, BBFrom)) {
+ BlockValueStack.push(std::make_pair(BBFrom, Val));
+ return false;
+ }
+
+ // if we couldn't compute the value on the edge, use the value from the BB
+ Result = getBlockValue(Val, BBFrom);
+ return true;
+}
+