/// This method returns null if there is no preheader for the loop.
///
BlockT *getLoopPreheader() const {
+ // Keep track of nodes outside the loop branching to the header...
+ BlockT *Out = getLoopPredecessor();
+ if (!Out) return 0;
+
+ // Make sure there is only one exit out of the preheader.
+ typedef GraphTraits<BlockT*> BlockTraits;
+ typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out);
+ ++SI;
+ if (SI != BlockTraits::child_end(Out))
+ return 0; // Multiple exits from the block, must not be a preheader.
+
+ // The predecessor has exactly one successor, so it is a preheader.
+ return Out;
+ }
+
+ /// getLoopPredecessor - If the given loop's header has exactly one unique
+ /// predecessor outside the loop, return it. Otherwise return null.
+ /// This is less strict that the loop "preheader" concept, which requires
+ /// the predecessor to have exactly one successor.
+ ///
+ BlockT *getLoopPredecessor() const {
// Keep track of nodes outside the loop branching to the header...
BlockT *Out = 0;
// Make sure there is only one exit out of the preheader.
assert(Out && "Header of loop has no predecessors from outside loop?");
- typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out);
- ++SI;
- if (SI != BlockTraits::child_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;
}