[IVUsers] don't bail out of normalizing non-affine add recs

[sanjoy]

Summary

In a previous change I changed SCEV's normalization / denormalization
to work with non-affine add recs. So the bailout in IVUsers can be
removed.

[sanjoy]

ping!

[davide]

test/Analysis/IVUsers/quadradic-exit-value.ll

33–61

Can you keep the test?

[atrick]

Yeah, it seems like you should have the positive version of this test.
Otherwise, lgtm.

lib/Analysis/IVUsers.cpp

if (AddUserToIVUsers) {
       // Okay, we found a user that we cannot reduce.
       IVStrideUse &NewUse = AddUser(User, I);
       // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
       // The regular return value here is discarded; instead of recording
       // it, we just recompute it when we need it.
       const SCEV *OriginalISE = ISE;
 
       auto NormalizePred = [&](const SCEVAddRecExpr *AR) {
-        // We only allow affine AddRecs to be normalized, otherwise we would not
-        // be able to correctly denormalize.
-        // e.g. {1,+,3,+,2} == {-2,+,1,+,2} + {3,+,2}
-        // Normalized form:   {-2,+,1,+,2}
-        // Denormalized form: {1,+,3,+,2}
-        //
-        // However, denormalization would use a different step expression than
-        // normalization (see getPostIncExpr), generating the wrong final
-        // expression: {-2,+,1,+,2} + {1,+,2} => {-1,+,3,+,2}
         auto *L = AR->getLoop();
-        bool Result =
-            AR->isAffine() && IVUseShouldUsePostIncValue(User, I, L, DT);
+        bool Result = IVUseShouldUsePostIncValue(User, I, L, DT);
         if (Result)
           NewUse.PostIncLoops.insert(L);
         return Result;
       };
 
       ISE = normalizeForPostIncUseIf(ISE, NormalizePred, *SE);
 
       // PostIncNormalization effectively simplifies the expression under

test/Analysis/IVUsers/quadradic-exit-value.ll

foo.loop:
   %indvar.next = add i64 %indvar, 1
   %c = icmp eq i64 %indvar.next, %n
   br i1 %c, label %exit, label %foo.loop
 
 exit:
   %r = mul i64 %indvar.next, %indvar.next
   ret i64 %r
 }
-
-; PR15470: LSR miscompile. The test2 function should return '1'.
-;
-; SCEV does not know how to denormalize chained recurrences, so make
-; sure they aren't marked as post-inc users.
-;
-; CHECK-LABEL: IV Users for loop %test2.loop
-; CHECK-NO-LCSSA: %sext.us = {0,+,(16777216 + (-16777216 * %sub.us))<nuw><nsw>,+,33554432}<%test2.loop> in %f = ashr i32 %sext.us, 24
-define i32 @test2() {
-entry:
-  br label %test2.loop
-
-test2.loop:
-  %inc1115.us = phi i32 [ 0, %entry ], [ %inc11.us, %test2.loop ]
-  %inc11.us = add nsw i32 %inc1115.us, 1
-  %cmp.us = icmp slt i32 %inc11.us, 2
-  br i1 %cmp.us, label %test2.loop, label %for.end
-
-for.end:
-  %tobool.us = icmp eq i32 %inc1115.us, 0
-  %sub.us = select i1 %tobool.us, i32 0, i32 0
-  %mul.us = shl i32 %inc1115.us, 24
-  %sub.cond.us = sub nsw i32 %inc1115.us, %sub.us
-  %sext.us = mul i32 %mul.us, %sub.cond.us
-  %f = ashr i32 %sext.us, 24
-  br label %exit
-
-exit:
-  ret i32 %f
-}