[MemProf] Consolidate increments in callee matching code (#99385)

Summary:
To facilitate some follow on changes, consolidate the incrementing of
the edge iterator used during callee matching to the for loop statement.
This requires an additional adjustment in the case of tail call
handling.

Test Plan: 

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Tasks: 

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Differential Revision: https://phabricator.intern.facebook.com/D60251644

Author: teresajohnson

llvm/lib/Transforms/IPO/MemProfContextDisambiguation.cpp

@@ -505,9 +505,8 @@ class CallsiteContextGraph {
   /// we were able to identify the call chain through intermediate tail calls.
   /// In the latter case new context nodes are added to the graph for the
   /// identified tail calls, and their synthesized nodes are added to
-  /// TailCallToContextNodeMap. The EdgeIter is updated in either case to the
-  /// next element after the input position (either incremented or updated after
-  /// removing the old edge).
+  /// TailCallToContextNodeMap. The EdgeIter is updated in the latter case for
+  /// the updated edges and to prepare it for an increment in the caller.
   bool
   calleesMatch(CallTy Call, EdgeIter &EI,
                MapVector<CallInfo, ContextNode *> &TailCallToContextNodeMap);
@@ -1835,12 +1834,11 @@ void CallsiteContextGraph<DerivedCCG, FuncTy,
     assert(Node->Clones.empty());
     // Check all node callees and see if in the same function.
     auto Call = Node->Call.call();
-    for (auto EI = Node->CalleeEdges.begin(); EI != Node->CalleeEdges.end();) {
+    for (auto EI = Node->CalleeEdges.begin(); EI != Node->CalleeEdges.end();
+         ++EI) {
       auto Edge = *EI;
-      if (!Edge->Callee->hasCall()) {
-        ++EI;
+      if (!Edge->Callee->hasCall())
         continue;
-      }
       assert(NodeToCallingFunc.count(Edge->Callee));
       // Check if the called function matches that of the callee node.
       if (calleesMatch(Call, EI, TailCallToContextNodeMap))
@@ -1889,16 +1887,12 @@ bool CallsiteContextGraph<DerivedCCG, FuncTy, CallTy>::calleesMatch(
   // calls between the profiled caller and callee.
   std::vector<std::pair<CallTy, FuncTy *>> FoundCalleeChain;
   if (!calleeMatchesFunc(Call, ProfiledCalleeFunc, CallerFunc,
-                         FoundCalleeChain)) {
-    ++EI;
+                         FoundCalleeChain))
     return false;
-  }
 
   // The usual case where the profiled callee matches that of the IR/summary.
-  if (FoundCalleeChain.empty()) {
-    ++EI;
+  if (FoundCalleeChain.empty())
     return true;
-  }
 
   auto AddEdge = [Edge, &EI](ContextNode *Caller, ContextNode *Callee) {
     auto *CurEdge = Callee->findEdgeFromCaller(Caller);
@@ -1960,6 +1954,13 @@ bool CallsiteContextGraph<DerivedCCG, FuncTy, CallTy>::calleesMatch(
   Edge->Callee->eraseCallerEdge(Edge.get());
   EI = Edge->Caller->CalleeEdges.erase(EI);
 
+  // To simplify the increment of EI in the caller, subtract one from EI.
+  // In the final AddEdge call we would have either added a new callee edge,
+  // to Edge->Caller, or found an existing one. Either way we are guaranteed
+  // that there is at least one callee edge.
+  assert(!Edge->Caller->CalleeEdges.empty());
+  --EI;
+
   return true;
 }