From: Max Kazantsev <max.kazantsev@azul.com>
Date: Wed, 17 May 2017 04:09:14 +0000 (+0000)
Subject: [SCEV] Always sort AddRecExprs from different loops by dominance
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=d15a6186dabf3b23c4c9e248a8dffce6d44e1956;p=llvm

[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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303235 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 69fb1ae7dfe..a746ddfd7a6 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -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.