[AMDGPU] Simplify collectReachableCallees. NFCI.

[foad]

Summary

Don't use SCC iterators when we're only interested in reachability.
Use df_begin/df_end inline to find reachable nodes.

[rampitec]

LGTM

llvm/lib/Target/AMDGPU/Utils/AMDGPULDSUtils.cpp

55

Reformat the whole comment before the submission.

llvm/lib/Target/AMDGPU/Utils/AMDGPULDSUtils.cpp

 //===- AMDGPULDSUtils.cpp -------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // AMDGPU LDS related helper utility functions.
 //
 //===----------------------------------------------------------------------===//
 
 #include "AMDGPULDSUtils.h"
 #include "Utils/AMDGPUBaseInfo.h"
-#include "llvm/ADT/SCCIterator.h"
+#include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/Analysis/CallGraph.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/ReplaceConstant.h"
 
 using namespace llvm;
 
 namespace llvm {
for (auto GI = ECNode->begin(), GE = ECNode->end(); GI != GE; ++GI) {
       auto *CGN = GI->second;
       auto *F = CGN->getFunction();
       if (!F || F->isDeclaration() || AMDGPU::isKernelCC(F))
         continue;
       AddressTakenFunctions.insert(CGN);
     }
   }
 
-  // For a given caller node, collect all reachable callee nodes.
-  SmallPtrSet<CallGraphNode *, 8> collectCGNodes(CallGraphNode *CGN) {
-    SmallPtrSet<CallGraphNode *, 8> CGNodes;
-
-    for (scc_iterator<CallGraphNode *> I = scc_begin(CGN); !I.isAtEnd(); ++I) {
-      const std::vector<CallGraphNode *> &SCC = *I;
-      assert(!SCC.empty() && "SCC with no functions?");
-      for (auto *CGNode : SCC)
-        CGNodes.insert(CGNode);
-    }
-
-    return CGNodes;
-  }
-
   // For given kernel, collect all its reachable non-kernel functions.
   SmallPtrSet<Function *, 8> collectReachableCallees(Function *K) {
     SmallPtrSet<Function *, 8> ReachableCallees;
 
     // Call graph node which represents this kernel.
     auto *KCGN = CG[K];
 
-    // Collect all reachable call graph nodes from the node representing this
-    // kernel.
-    SmallPtrSet<CallGraphNode *, 8> CGNodes = collectCGNodes(KCGN);
-
-    // Go through collected reachable nodes, visit all thier call sites, if the
+    // Go through all call graph nodes reachable from the node representing this
+    // kernel, visit all thier call sites, if the
     // call site is direct, add corresponding callee to reachable callee set, if
     // it is indirect, resolve the indirect call site to potential reachable
     // callees, add them to reachable callee set, and repeat the process for the
     // newly added potential callee nodes.
     //
     // FIXME: Need to handle bit-casted function pointers.
     //
-    SmallVector<CallGraphNode *, 8> CGNStack(CGNodes.begin(), CGNodes.end());
+    SmallVector<CallGraphNode *, 8> CGNStack(df_begin(KCGN), df_end(KCGN));
     SmallPtrSet<CallGraphNode *, 8> VisitedCGNodes;
     while (!CGNStack.empty()) {
       auto *CGN = CGNStack.pop_back_val();
 
       if (!VisitedCGNodes.insert(CGN).second)
         continue;
 
       for (auto GI = CGN->begin(), GE = CGN->end(); GI != GE; ++GI) {
         auto *RCB = cast<CallBase>(GI->first.getValue());
         auto *RCGN = GI->second;
 
         if (auto *DCallee = RCGN->getFunction()) {
           ReachableCallees.insert(DCallee);
         } else if (RCB->isIndirectCall()) {
           auto *RCBFTy = RCB->getFunctionType();
           for (auto *ACGN : AddressTakenFunctions) {
             auto *ACallee = ACGN->getFunction();
             if (ACallee->getFunctionType() == RCBFTy) {
               ReachableCallees.insert(ACallee);
-              SmallPtrSet<CallGraphNode *, 8> IGCNNodes = collectCGNodes(ACGN);
-              for (auto *IGCN : IGCNNodes)
-                CGNStack.push_back(IGCN);
+              CGNStack.append(df_begin(ACGN), df_end(ACGN));
             }
           }
         }
       }
     }
 
     return ReachableCallees;
   }