[PATCH] D33228: [SCEV] Always sort AddRecExprs from different loops by dominance

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
Herald added a subscriber: mzolotukhin.

Sorting of AddRecExprs by loop nesting does not make sense since we only invoke the CompareSCEVComplexity for AddRecExprs that are used by one SCEV. This guarantees that there is always a dominance relationship between them. This patch removes the sorting by nesting which is a dead code in current usage of this function.


https://reviews.llvm.org/D33228

Files:
  lib/Analysis/ScalarEvolution.cpp


Index: lib/Analysis/ScalarEvolution.cpp
===================================================================
--- lib/Analysis/ScalarEvolution.cpp
+++ lib/Analysis/ScalarEvolution.cpp
@@ -629,19 +629,18 @@
     const SCEVAddRecExpr *LA = cast<SCEVAddRecExpr>(LHS);
     const SCEVAddRecExpr *RA = cast<SCEVAddRecExpr>(RHS);
 
-    // If there is a dominance relationship between the loops, sort by the
-    // dominance. Otherwise, sort by depth.
+    // There is always a dominance between two recs that are used by one
+    // SCEV, so we can safely sort recs by loop header dominance.
     const Loop *LLoop = LA->getLoop(), *RLoop = RA->getLoop();
     if (LLoop != RLoop) {
       const BasicBlock *LHead = LLoop->getHeader(), *RHead = RLoop->getHeader();
       assert(LHead != RHead && "Two loops share the same header?");
       if (DT.dominates(LHead, RHead))
         return 1;
-      else if (DT.dominates(RHead, LHead))
-        return -1;
-      unsigned LDepth = LLoop->getLoopDepth(), RDepth = RLoop->getLoopDepth();
-      if (LDepth != RDepth)
-        return (int)LDepth - (int)RDepth;
+      else
+        assert(DT.dominates(RHead, LHead) &&
+               "No dominance between recurrencies used by one SCEV?");
+      return -1;
     }
 
     // Addrec complexity grows with operand count.


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