[ModuleInliner] Fix the heap maintenance (#69251)

With expensive checks enabled but without this patch, std::pop_heap
triggers an assertion failure.  This is because:

  updateAndCheckDecreased(Heap.front())

updates the priority associated with Heap.front(), so Heap may no
longer be a valid heap.  The libstdc++ version of std::pop_heap
requires that the entire range be a valid heap even though the core
task of std::pop_heap is just to swap the Heap.front() and
Heap.back().

This patch fixes the problem by:

- calling std::pop_heap to swap Heap.front() and Heap.back(),
- updating the priority of Heap.back(), and
- inserting Heap.back() back into the heap.

We could reduce the number of calls to updateAndCheckDecreased or the
number of elements being moved, but I think it's important to fix the
crash first.

Credit to Ivan Kosarev for identifying the problem and Liqiang Tao for
the analysis and initial version of the patch.

Author: kazutakahirata

llvm/lib/Analysis/InlineOrder.cpp

@@ -223,10 +223,12 @@ class PriorityInlineOrder : public InlineOrder<std::pair<CallBase *, int>> {
   // pushed right back into the heap. For simplicity, those cases where
   // the desirability of a call site increases are ignored here.
   void adjust() {
-    while (updateAndCheckDecreased(Heap.front())) {
-      std::pop_heap(Heap.begin(), Heap.end(), isLess);
+    std::pop_heap(Heap.begin(), Heap.end(), isLess);
+    while (updateAndCheckDecreased(Heap.back())) {
       std::push_heap(Heap.begin(), Heap.end(), isLess);
+      std::pop_heap(Heap.begin(), Heap.end(), isLess);
     }
+    std::push_heap(Heap.begin(), Heap.end(), isLess);
   }
 
 public: