[LoopNest] Add new utilites

[Whitney]

Summary

getLoopIndex() is added to get the loop index of a given loop.
getLoopsAtDepth() is added to get the loops in the nest at a given depth.

[Meinersbur]

llvm/include/llvm/Analysis/LoopNestAnalysis.h

120

Isn't it sufficient to return Loops[Depth - getOutermostLoop().getLoopDepth()]?

[Whitney]

llvm/include/llvm/Analysis/LoopNestAnalysis.h

120

When the loop nest is not perfect, there can be multiple loops at the same depth.

[Whitney]

ping

[Meinersbur]

LGTM

llvm/include/llvm/Analysis/LoopNestAnalysis.h

128

[suggestion]

[Whitney]

address review comment

llvm/include/llvm/Analysis/LoopNestAnalysis.h

public:
   }
 
   /// Return the loop at the given \p Index.
   Loop *getLoop(unsigned Index) const {
     assert(Index < Loops.size() && "Index is out of bounds");
     return Loops[Index];
   }
 
+  /// Get the loop index of the given loop \p L.
+  unsigned getLoopIndex(const Loop &L) const {
+    for (unsigned I = 0; I < getNumLoops(); ++I)
+      if (getLoop(I) == &L)
+        return I;
+    llvm_unreachable("Loop not in the loop nest");
+  }
+
   /// Return the number of loops in the nest.
   size_t getNumLoops() const { return Loops.size(); }
 
   /// Get the loops in the nest.
   ArrayRef<Loop *> getLoops() const { return Loops; }
 
+  /// Get the loops in the nest at the given \p Depth.
+  LoopVectorTy getLoopsAtDepth(unsigned Depth) const {
+    assert(Depth >= Loops.front()->getLoopDepth() &&
+           Depth <= Loops.back()->getLoopDepth() && "Invalid depth");
+    LoopVectorTy Result;
+    for (unsigned I = 0; I < getNumLoops(); ++I) {
+      Loop *L = getLoop(I);
+      if (L->getLoopDepth() == Depth)
+        Result.push_back(L);
+      else if (L->getLoopDepth() > Depth)
+        break;
+    }
+    return Result;
+  }
+
   /// Retrieve a vector of perfect loop nests contained in the current loop
   /// nest. For example, given the following  nest containing 4 loops, this
   /// member function would return {{L1,L2},{L3,L4}}.
   /// \code
   ///   for(i) // L1
   ///     for(j) // L2
   ///       <code>
   ///       for(k) // L3

llvm/unittests/Analysis/LoopNestTest.cpp

runTest(*M, "foo", [&](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
     const Loop *IL = LN.getInnermostLoop();
     EXPECT_NE(IL, nullptr);
     EXPECT_EQ(IL->getName(), "for.inner");
 
     // Ensure the loop nest is recognized as having 2 loops.
     const ArrayRef<Loop*> Loops = LN.getLoops();
     EXPECT_EQ(Loops.size(), 2ull);
 
+    // Ensure that we can obtain loops by depth.
+    LoopVectorTy LoopsAtDepth1 = LN.getLoopsAtDepth(1);
+    EXPECT_EQ(LoopsAtDepth1.size(), 1u);
+    EXPECT_EQ(LoopsAtDepth1[0], &OL);
+    LoopVectorTy LoopsAtDepth2 = LN.getLoopsAtDepth(2);
+    EXPECT_EQ(LoopsAtDepth2.size(), 1u);
+    EXPECT_EQ(LoopsAtDepth2[0], IL);
+
+    // Ensure that we can obtain the loop index of a given loop, and get back
+    // the loop with that index.
+    EXPECT_EQ(LN.getLoop(LN.getLoopIndex(OL)), &OL);
+    EXPECT_EQ(LN.getLoop(LN.getLoopIndex(*IL)), IL);
+
     // Ensure the loop nest is recognized as perfect in its entirety.
     const SmallVector<LoopVectorTy, 4> &PLV = LN.getPerfectLoops(SE);
     EXPECT_EQ(PLV.size(), 1ull);
     EXPECT_EQ(PLV.front().size(), 2ull);
 
     // Ensure the nest depth and perfect nest depth are computed correctly.
     EXPECT_EQ(LN.getNestDepth(), 2u);
     EXPECT_EQ(LN.getMaxPerfectDepth(), 2u);