Revert "[SCEV][NFC] Check NoWrap flags before lexicographical comparison of SCEVs"

This reverts r319889.

Unfortunately, wrapping flags are not a part of SCEV's identity (they
do not participate in computing a hash value or in equality
comparisons) and in fact they could be assigned after the fact w/o
rebuilding a SCEV.

Grep for const_cast's to see quite a few of examples, apparently all
for AddRec's at the moment.

So, if 2 expressions get built in 2 slightly different ways: one with
flags set in the beginning, the other with the flags attached later
on, we may end up with 2 expressions which are exactly the same but
have their operands swapped in one of the commutative N-ary
expressions, and at least one of them will have "sorted by complexity"
invariant broken.

2 identical SCEV's won't compare equal by pointer comparison as they
are supposed to.

A real-world reproducer is added as a regression test: the issue
described causes 2 identical SCEV expressions to have different order
of operands and therefore compare not equal, which in its turn
prevents LoadStoreVectorizer from vectorizing a pair of consecutive
loads.

On a larger example (the source of the test attached, which is a
bugpoint) I have seen even weirder behavior: adding a constant to an
existing SCEV changes the order of the existing terms, for instance,
getAddExpr(1, ((A * B) + (C * D))) returns (1 + (C * D) + (A * B)).

Differential Revision: https://reviews.llvm.org/D40645

llvm-svn: 340777

1 files changed, 0 insertions, 8 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index f82a9a6dd4f..5626e69398e 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -692,10 +692,6 @@ static int CompareSCEVComplexity(
     if (LNumOps != RNumOps)
       return (int)LNumOps - (int)RNumOps;
 
-    // Compare NoWrap flags.
-    if (LA->getNoWrapFlags() != RA->getNoWrapFlags())
-      return (int)LA->getNoWrapFlags() - (int)RA->getNoWrapFlags();
-
     // Lexicographically compare.
     for (unsigned i = 0; i != LNumOps; ++i) {
       int X = CompareSCEVComplexity(EqCacheSCEV, EqCacheValue, LI,
@@ -720,10 +716,6 @@ static int CompareSCEVComplexity(
     if (LNumOps != RNumOps)
       return (int)LNumOps - (int)RNumOps;
 
-    // Compare NoWrap flags.
-    if (LC->getNoWrapFlags() != RC->getNoWrapFlags())
-      return (int)LC->getNoWrapFlags() - (int)RC->getNoWrapFlags();
-
     for (unsigned i = 0; i != LNumOps; ++i) {
       int X = CompareSCEVComplexity(EqCacheSCEV, EqCacheValue, LI,
                                     LC->getOperand(i), RC->getOperand(i), DT,