[ModuleInliner] Remove InlineOrder::front (NFC)

InlineOrder::front is a remnant from the era when we had a nested
"while" loops in the module inliner, with the inner one grouping the
call sites with the same caller.

Now that we have a simple "while" loop draining the priority queue, we
can just use InlineOrder::pop.

Differential Revision: https://reviews.llvm.org/D134121

llvm/include/llvm/Analysis/InlineOrder.h

@@ -29,8 +29,6 @@ template <typename T> class InlineOrder {
 
   virtual T pop() = 0;
 
-  virtual const_reference front() = 0;
-
   virtual void erase_if(function_ref<bool(T)> Pred) = 0;
 
   bool empty() { return !size(); }

llvm/lib/Analysis/InlineOrder.cpp

@@ -169,14 +169,6 @@ class PriorityInlineOrder : public InlineOrder<std::pair<CallBase *, int>> {
     return Result;
   }
 
-  const_reference front() override {
-    assert(size() > 0);
-    adjust();
-
-    CallBase *CB = Heap.front();
-    return *InlineHistoryMap.find(CB);
-  }
-
   void erase_if(function_ref<bool(T)> Pred) override {
     auto PredWrapper = [=](CallBase *CB) -> bool {
       return Pred(std::make_pair(CB, 0));

llvm/lib/Transforms/IPO/ModuleInliner.cpp

@@ -182,22 +182,21 @@ PreservedAnalyses ModuleInlinerPass::run(Module &M,
 
   // Loop forward over all of the calls.
   while (!Calls->empty()) {
-    Function &F = *Calls->front().first->getCaller();
-    (void)F;
+    auto P = Calls->pop();
+    CallBase *CB = P.first;
+    const int InlineHistoryID = P.second;
+    Function &F = *CB->getCaller();
+    Function &Callee = *CB->getCalledFunction();
 
     LLVM_DEBUG(dbgs() << "Inlining calls in: " << F.getName() << "\n"
                       << "    Function size: " << F.getInstructionCount()
                       << "\n");
+    (void)F;
 
     auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & {
       return FAM.getResult<AssumptionAnalysis>(F);
     };
 
-    auto P = Calls->pop();
-    CallBase *CB = P.first;
-    const int InlineHistoryID = P.second;
-    Function &Callee = *CB->getCalledFunction();
-
     if (InlineHistoryID != -1 &&
         inlineHistoryIncludes(&Callee, InlineHistoryID, InlineHistory)) {
       setInlineRemark(*CB, "recursive");