[SCEV] Do not insert if it is already in cache

This is fix for the crash caused by ScalarEvolution::getTruncateExpr.

It expects that if it checked the condition that SCEV is not in UniqueSCEVs cache in
the beginning that it will not be there inside this method.

However during recursion and transformation/simplification for sub expression,
it is possible that these modifications will end up with the same SCEV as we started from.

So we must always check whether SCEV is in cache and do not insert item if it is already there.

Reviewers: sanjoy, mkazantsev, craig.topper	
Reviewed By: sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D41380

llvm-svn: 321472

1 files changed, 10 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 2a8088dc445..f34549ae52b 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -1268,7 +1268,11 @@ const SCEV *ScalarEvolution::getTruncateExpr(const SCEV *Op,
     }
     if (!hasTrunc)
       return getAddExpr(Operands);
-    UniqueSCEVs.FindNodeOrInsertPos(ID, IP);  // Mutates IP, returns NULL.
+    // In spite we checked in the beginning that ID is not in the cache,
+    // it is possible that during recursion and different modification
+    // ID came to cache, so if we found it, just return it.
+    if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP))
+      return S;
   }
 
   // trunc(x1*x2*...*xN) --> trunc(x1)*trunc(x2)*...*trunc(xN) if we can
@@ -1284,7 +1288,11 @@ const SCEV *ScalarEvolution::getTruncateExpr(const SCEV *Op,
     }
     if (!hasTrunc)
       return getMulExpr(Operands);
-    UniqueSCEVs.FindNodeOrInsertPos(ID, IP);  // Mutates IP, returns NULL.
+    // In spite we checked in the beginning that ID is not in the cache,
+    // it is possible that during recursion and different modification
+    // ID came to cache, so if we found it, just return it.
+    if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP))
+      return S;
   }
 
   // If the input value is a chrec scev, truncate the chrec's operands.