[SCEV] Add a reproducer where SCEV doesn't conclude divisibility.

llvm/unittests/Analysis/ScalarEvolutionTest.cpp

runWithSE(*M, "foo", [](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
     auto *ScevIV = SE.getSCEV(getInstructionByName(F, "iv"));
     const Loop *L = cast<SCEVAddRecExpr>(ScevIV)->getLoop();
 
     const SCEV *ITC = SE.getConstantMaxTripCountFromArray(L);
     EXPECT_TRUE(isa<SCEVCouldNotCompute>(ITC));
   });
 }
 
+TEST_F(ScalarEvolutionsTest, WrongDivisibilty) {
+  LLVMContext C;
+  SMDiagnostic Err;
+  std::unique_ptr<Module> M = parseAssemblyString("define void @foo(i32 %num) { "
+                                                  "  ret void "
+                                                  "} ",
+                                                  Err, C);
+
+  ASSERT_TRUE(M && "Could not parse module?");
+  ASSERT_TRUE(!verifyModule(*M) && "Must have been well formed!");
+
+  runWithSE(*M, "foo", [](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
+    auto *ScevIV = SE.getSCEV(getArgByName(F, "num"));
+    // create the following SCEV:
+    // 8 umax (32 umin (4 * (%num /u 4))<nuw>)
+    // SCEV doesn't conclude it divides by 4.
+    APInt Four(32, 4);
+    APInt ThirtyTwo(32, 32);
+    APInt Eight(32, 8);
+    auto Constant4 = SE.getConstant(Four);
+    auto Constant32 = SE.getConstant(ThirtyTwo);
+    auto Constant8 = SE.getConstant(Eight);
+    auto Mul = SE.getMulExpr(SE.getUDivExpr(ScevIV, Constant4), Constant4);
+    auto Min = SE.getUMinExpr(Mul, Constant32);
+    auto Max = SE.getUMaxExpr(Min, Constant8);
+    auto Rem = SE.getURemExpr(Max, Constant4);
+    ASSERT_TRUE(!Rem->isZero());
+  });
+}
+
 }  // end namespace llvm