diff --git a/lib/Analysis/LoopInfo.cpp b/lib/Analysis/LoopInfo.cpp index e12d3175983..b8315ac1d73 100644 --- a/lib/Analysis/LoopInfo.cpp +++ b/lib/Analysis/LoopInfo.cpp @@ -373,12 +373,36 @@ BasicBlock *Loop::getLoopPreheader() const { if (SI != succ_end(Out)) return 0; // Multiple exits from the block, must not be a preheader. - // If there is exactly one preheader, return it. If there was zero, then Out // is still null. return Out; } +/// getLoopLatch - If there is a latch block for this loop, return it. A +/// latch block is the canonical backedge for a loop. A loop header in normal +/// form has two edges into it: one from a preheader and one from a latch +/// block. +BasicBlock *Loop::getLoopLatch() const { + BasicBlock *Header = getHeader(); + pred_iterator PI = pred_begin(Header), PE = pred_end(Header); + if (PI == PE) return 0; // no preds? + + BasicBlock *Latch = 0; + if (contains(*PI)) + Latch = *PI; + ++PI; + if (PI == PE) return 0; // only one pred? + + if (contains(*PI)) { + if (Latch) return 0; // multiple backedges + Latch = *PI; + } + ++PI; + if (PI != PE) return 0; // more than two preds + + return Latch; +} + /// getCanonicalInductionVariable - Check to see if the loop has a canonical /// induction variable: an integer recurrence that starts at 0 and increments by /// one each time through the loop. If so, return the phi node that corresponds