[SCEV] Add support for x != 0 to CollectCondition.

Add support for NE predicates with 0 constants. Those can be translated
to UMaxExpr(x, 1).

Author: fhahn

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -12622,6 +12622,12 @@ const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
       if (isa<SCEVConstant>(RHS))
         RewriteMap[LHSUnknown->getValue()] = RHS;
       break;
+    case CmpInst::ICMP_NE:
+      if (isa<SCEVConstant>(RHS) &&
+          cast<SCEVConstant>(RHS)->getValue()->isNullValue())
+        RewriteMap[LHSUnknown->getValue()] =
+            getUMaxExpr(LHS, getOne(RHS->getType()));
+      break;
     default:
       break;
     }

llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll

@@ -249,7 +249,7 @@ exit:
 define void @test_guard_ult_ne(i32* nocapture readonly %data, i64 %count) {
 ; CHECK-LABEL: @test_guard_ult_ne
 ; CHECK:       Loop %loop: backedge-taken count is (-1 + %count)
-; CHECK-NEXT:  Loop %loop: max backedge-taken count is -2
+; CHECK-NEXT:  Loop %loop: max backedge-taken count is 3
 ; CHECK-NEXT:  Loop %loop: Predicated backedge-taken count is (-1 + %count)
 ;
 entry: