[FIX] Bug fix for a floormod rewrite simplify rule (#8852)

* Update rewrite_simplify.cc

* Update test_arith_rewrite_simplify.py

* Update test_arith_rewrite_simplify.py

* Update test_arith_rewrite_simplify.py

src/arith/rewrite_simplify.cc

@@ -858,14 +858,18 @@ PrimExpr RewriteSimplifier::Impl::VisitExpr_(const FloorModNode* op) {
       ModularSet bmod = analyzer_->modular_set(b1.Eval());
       int64_t ramp_min = floordiv(bmod->base, c2val);
       int64_t ramp_max = floordiv(bmod->base + (lanes.Eval() - 1) * c1val, c2val);
-      if (bmod->coeff % c2val == 0) {
-        if (ramp_min == ramp_max) {
+      if (ramp_min == ramp_max) {
+        // If b1 can devide c2
+        if (bmod->coeff % c2val == 0) {
           return ramp(floormod(bmod->base, c2), c1, lanes).Eval();
-        } else {
-          return floormod(ramp(floormod(bmod->base, c2), c1, lanes), broadcast(c2, lanes)).Eval();
         }
-      } else if (c2val % bmod->coeff == 0 && ramp_min == ramp_max) {
-        return ramp(floormod(b1, c2), c1, lanes).Eval();
+        // If all indices can be guaranteed to settle inside a coeff range
+        if (c2val % bmod->coeff == 0 && bmod->base + (lanes.Eval() - 1) * c1val < bmod->coeff) {
+          return ramp(floormod(b1, c2), c1, lanes).Eval();
+        }
+      }
+      if (bmod->coeff % c2val == 0) {
+        return floormod(ramp(floormod(bmod->base, c2), c1, lanes), broadcast(c2, lanes)).Eval();
       }
     }
   }

tests/python/unittest/test_arith_rewrite_simplify.py

@@ -101,15 +101,16 @@ def test_vector_simplify():
     ck.verify(
         fld(tvm.tir.Ramp(x * 4, 1, 5), tvm.tir.Broadcast(64, 5)),
         fld(tvm.tir.Ramp(x * 4, 1, 5), tvm.tir.Broadcast(64, 5)),
-    )
+    )  # Example negative case: x = 15; [60, 61, 62, 63, 64] / 64 = [0, 0, 0, 0, 1]
     ck.verify(
         fld(tvm.tir.Ramp(x * 4 + 3, 1, 4), tvm.tir.Broadcast(64, 4)),
         fld(tvm.tir.Ramp(x * 4 + 3, 1, 4), tvm.tir.Broadcast(64, 4)),
-    )
+    )  # Example negative case: x = 15; [63, 64, 65, 66] % 64 = [0, 1, 1, 1]
     ck.verify(
         fld(tvm.tir.Ramp(x * 7, 1, 4), tvm.tir.Broadcast(64, 4)),
         fld(tvm.tir.Ramp(x * 7, 1, 4), tvm.tir.Broadcast(64, 4)),
-    )
+    )  # Example negative case: x = 9; [63, 70, 77, 84] % 64 = [0, 1, 1, 1]
+
     # floor mod
     ck.verify(flm(y.astype("int32x2"), x.astype("int32x2")), flm(y, x).astype("int32x2"))
     ck.verify(flm(tvm.tir.Ramp(x, 4, 4), 2), tvm.tir.Broadcast(flm(x, 2), 4))
@@ -136,16 +137,21 @@ def test_vector_simplify():
         flm(tvm.tir.Ramp(x * 8, 2, 4), tvm.tir.Broadcast(64, 4)), tvm.tir.Ramp(flm(x * 8, 64), 2, 4)
     )
     ck.verify(
-        flm(tvm.tir.Ramp(x * 4, 1, 5), tvm.tir.Broadcast(64, 5)), tvm.tir.Ramp(flm(x * 4, 64), 1, 5)
-    )
+        flm(tvm.tir.Ramp(x * 4, 1, 5), tvm.tir.Broadcast(64, 5)),
+        flm(tvm.tir.Ramp(x * 4, 1, 5), tvm.tir.Broadcast(64, 5)),
+    )  # Example negative case: x = 15; [60, 61, 62, 63, 64] % 64 = [60, 61, 62, 63, 0]
     ck.verify(
         flm(tvm.tir.Ramp(x * 4 + 3, 1, 4), tvm.tir.Broadcast(64, 4)),
-        tvm.tir.Ramp(flm(x * 4 + 3, 64), 1, 4),
-    )
+        flm(tvm.tir.Ramp(x * 4 + 3, 1, 4), tvm.tir.Broadcast(64, 4)),
+    )  # Example negative case: x = 15; [63, 64, 65, 66] % 64 = [63, 0, 1, 2]
+    ck.verify(
+        flm(tvm.tir.Ramp(x * 2, 1, 8), tvm.tir.Broadcast(20, 8)),
+        flm(tvm.tir.Ramp(x * 2, 1, 8), tvm.tir.Broadcast(20, 8)),
+    )  # Example negative case: x = 9; [18, 19, 20, ..., 25] % 20 = [18, 19, 0, 1, ..., 5]
     ck.verify(
         flm(tvm.tir.Ramp(x * 7, 1, 4), tvm.tir.Broadcast(64, 4)),
         flm(tvm.tir.Ramp(x * 7, 1, 4), tvm.tir.Broadcast(64, 4)),
-    )
+    )  # Example negative case: x = 9; [63, 70, 77, 84] % 64 = [63, 6, 13, 20]
 
     # Min/Max rules
     vx = te.var("vx", dtype="int32x2")