trim const in UOp div_folding (#5982)

simplify `(4*x+4*y+7)//16` to `(x+y+1)//4`.
fixed `GPU=1 UOP_IS_SYMBOLIC=1 IMAGE=2 python -m pytest test/test_ops.py -k conv`

test/unit/test_symbolic.py

@@ -145,6 +145,9 @@ class TestSymbolic(unittest.TestCase):
   def test_sum_div_some_factor(self):
     self.helper_test_variable(Node.sum([Variable("a", 0, 7)*5, Variable("b", 0, 3)*4]) // 2, 0, 23, "(((a*5)//2)+(b*2))")
 
+  def test_sum_div_trim_const(self):
+    self.helper_test_variable((Variable("a", 0, 7)*4 + Variable("b", 0, 3)*4 + 7) // 16, 0, 2, "((1+a+b)//4)")
+
   def test_sum_div_some_partial_factor(self):
     self.helper_test_variable(Node.sum([Variable("a", 0, 7)*6, Variable("b", 0, 7)*6]) // 16, 0, 5, "(((a*3)+(b*3))//8)")
     self.helper_test_variable(Node.sum([NumNode(16), Variable("a", 0, 7)*6, Variable("b", 0, 7)*6]) // 16, 1, 6, "((((a*3)+(b*3))//8)+1)")

test/unit/test_uop_symbolic.py

@@ -203,6 +203,9 @@ class TestSymbolic(unittest.TestCase):
   def test_sum_div_some_factor(self):
     self.helper_test_variable(Node.sum([Variable("a", 0, 7)*5, Variable("b", 0, 3)*4]) // 2, 0, 23, {"(((a*5)//2)+(b*2))", "((b*2)+((a*5)//2))"})
 
+  def test_sum_div_trim_const(self):
+    self.helper_test_variable((Variable("a", 0, 7)*4 + Variable("b", 0, 3)*4 + 7) // 16, 0, 2, {"((1+a+b)//4)", "((a+b+1)//4)"})
+
   def test_sum_div_some_partial_factor(self):
     self.helper_test_variable(Node.sum([Variable("a", 0, 7)*6, Variable("b", 0, 7)*6]) // 16, 0, 5, "(((a*3)+(b*3))//8)")
     self.helper_test_variable(Node.sum([NumNode(16), Variable("a", 0, 7)*6, Variable("b", 0, 7)*6]) // 16, 1, 6, "((((a*3)+(b*3))//8)+1)")

tinygrad/codegen/uopgraph.py

@@ -115,10 +115,11 @@ def div_folding(x:UOp, c:int) -> Optional[UOp]:
     something_changed = True
     quotient.append(x.const(rem_const//c))
     rem_const = rem_const%c
+  # make const a multiple of gcd
+  if c > 0 and rem_const > 0 and rem_const % gcd != 0:
+    something_changed = True
+    rem_const = (rem_const//gcd)*gcd
   if rem_const != 0:
-    if 0 < rem_const < gcd: something_changed = True  # cancel the const
-    else:
-      # only include rem_const in remainder if it's not cancelled
     gcd = math.gcd(gcd, rem_const)
     remainder.append(x.const(rem_const))