[SCEV] Use isKnownViaNonRecursiveReasoning for smax simplification

[loladiro]

Summary

Commit
rL331949: SCEV] Do not use induction in isKnownPredicate for simplification umax

changed the codepath for umax from isKnownPredicate to
isKnownViaNonRecursiveReasoning to avoid compile time blow up (and as
I found out also stack overflows). However, there is an exact copy of
the code for umax that was lacking this change. In D50167 I want to unify
these codepaths, but to avoid that being a behavior change for the smax
case, pull this independent bit out of it.

[sanjoy]

and as I found out also stack overflows

For posterity, do you have some example IR and/or stack traces that you could attach to the commit message, or make a test case out of?

[loladiro]

In D61166#1481838, @sanjoy wrote:

and as I found out also stack overflows

For posterity, do you have some example IR and/or stack traces that you could attach to the commit message, or make a test case out of?

I looked around in my notes from back when I did that patch, but doesn't look like I recorded it. I think all I did was try changing umax back to isKnownPredicate and running the test suite.

llvm/trunk/lib/Analysis/ScalarEvolution.cpp

#endif
   }
 
   // Okay, check to see if the same value occurs in the operand list twice.  If
   // so, delete one.  Since we sorted the list, these values are required to
   // be adjacent.
   for (unsigned i = 0, e = Ops.size()-1; i != e; ++i)
     //  X smax Y smax Y  -->  X smax Y
     //  X smax Y         -->  X, if X is always greater than Y
-    if (Ops[i] == Ops[i+1] ||
-        isKnownPredicate(ICmpInst::ICMP_SGE, Ops[i], Ops[i+1])) {
+    if (Ops[i] == Ops[i + 1] || isKnownViaNonRecursiveReasoning(
+                                    ICmpInst::ICMP_SGE, Ops[i], Ops[i + 1])) {
       Ops.erase(Ops.begin()+i+1, Ops.begin()+i+2);
       --i; --e;
-    } else if (isKnownPredicate(ICmpInst::ICMP_SLE, Ops[i], Ops[i+1])) {
+    } else if (isKnownViaNonRecursiveReasoning(ICmpInst::ICMP_SLE, Ops[i],
+                                               Ops[i + 1])) {
       Ops.erase(Ops.begin()+i, Ops.begin()+i+1);
       --i; --e;
     }
 
   if (Ops.size() == 1) return Ops[0];
 
   assert(!Ops.empty() && "Reduced smax down to nothing!");