[llvm] r303235 - [SCEV] Always sort AddRecExprs from different loops by dominance

[Max Kazantsev via llvm-commits]

Author: mkazantsev
Date: Tue May 16 23:09:14 2017
New Revision: 303235

URL: http://llvm.org/viewvc/llvm-project?rev=303235&view=rev
Log:
[SCEV] Always sort AddRecExprs from different loops by dominance

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.

Reviewed By: sanjoy

Differential Revision: https://reviews.llvm.org/D33228

Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=303235&r1=303234&r2=303235&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Tue May 16 23:09:14 2017
@@ -629,19 +629,19 @@ static int CompareSCEVComplexity(
     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. We require such order in getAddExpr.
+    // There is always a dominance between two recs that are used by one SCEV,
+    // so we can safely sort recs by loop header dominance. We require such
+    // order in getAddExpr.
     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 recurrences used by one SCEV?");
+      return -1;
     }
 
     // Addrec complexity grows with operand count.