[llvm] b0b2bf3 - [NFCI][LoopDeletion] Only query SCEV about loop successor if another successor is also in loop

[Max Kazantsev via llvm-commits]

Author: Max Kazantsev
Date: 2021-05-27T12:44:22+07:00
New Revision: b0b2bf3b5da950679db1431aae431a6dedea2245

URL: https://github.com/llvm/llvm-project/commit/b0b2bf3b5da950679db1431aae431a6dedea2245
DIFF: https://github.com/llvm/llvm-project/commit/b0b2bf3b5da950679db1431aae431a6dedea2245.diff

LOG: [NFCI][LoopDeletion] Only query SCEV about loop successor if another successor is also in loop

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/LoopDeletion.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
index 41be776ec141..14eb07ab17e6 100644
--- a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
@@ -267,10 +267,10 @@ static bool canProveExitOnFirstIteration(Loop *L, DominatorTree &DT,
     ICmpInst::Predicate Pred;
     Value *LHS, *RHS;
     const BasicBlock *IfTrue, *IfFalse;
+    auto *Term = BB->getTerminator();
     // TODO: Handle switches.
-    if (!match(BB->getTerminator(),
-               m_Br(m_ICmp(Pred, m_Value(LHS), m_Value(RHS)),
-                    m_BasicBlock(IfTrue), m_BasicBlock(IfFalse)))) {
+    if (!match(Term, m_Br(m_ICmp(Pred, m_Value(LHS), m_Value(RHS)),
+                          m_BasicBlock(IfTrue), m_BasicBlock(IfFalse)))) {
       MarkAllSuccessorsLive(BB);
       continue;
     }
@@ -283,13 +283,16 @@ static bool canProveExitOnFirstIteration(Loop *L, DominatorTree &DT,
     // Can we prove constant true or false for this condition?
     const SCEV *LHSS = getSCEVOnFirstIteration(LHS, L, SE, FirstIterSCEV);
     const SCEV *RHSS = getSCEVOnFirstIteration(RHS, L, SE, FirstIterSCEV);
-    // TODO: isKnownPredicateAt is more powerful, but it's too compile time
-    // consuming. So we avoid using it here.
-    if (SE.isKnownPredicate(Pred, LHSS, RHSS))
-      MarkLiveEdge(BB, BB->getTerminator()->getSuccessor(0));
-    else if (SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), LHSS,
-                                 RHSS))
-      MarkLiveEdge(BB, BB->getTerminator()->getSuccessor(1));
+        // Only query for liveness of in-loop edge if another successor is also
+        // in-loop.
+        // TODO: isKnownPredicateAt is more powerful, but it's too compile time
+        // consuming. So we avoid using it here.
+        if (L->contains(Term->getSuccessor(1)) &&
+            SE.isKnownPredicate(Pred, LHSS, RHSS))
+        MarkLiveEdge(BB, Term->getSuccessor(0));
+    else if (L->contains(Term->getSuccessor(0)) &&
+             SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), LHSS,
+                                 RHSS)) MarkLiveEdge(BB, Term->getSuccessor(1));
     else
       MarkAllSuccessorsLive(BB);
   }