tests/micropython: Test that viper offset stores don't clobber base reg.

When running the viper boundary tests, assert that the offset stores don't
clobber the base register, which is saved and temporarily modified on some
architectures.

Signed-off-by: Chris Webb <chris@arachsys.com>

tests/micropython/viper_ptr16_store_boundary_intbig.py

@@ -3,7 +3,9 @@
 SET_TEMPLATE = """
 @micropython.viper
 def set{off}(dest: ptr16):
+    saved = dest
     dest[{off}] = {val}
+    assert int(saved) == int(dest)
 set{off}(buffer)
 print(hex(get_index(buffer, {off})))
 """
@@ -15,7 +17,9 @@ MASK = (1 << (8 * SIZE)) - 1
 
 @micropython.viper
 def set_index(dest: ptr16, i: int, val: uint):
+    saved = dest
     dest[i] = val
+    assert int(saved) == int(dest)
 
 
 def get_index(src, i):

tests/micropython/viper_ptr32_store_boundary_intbig.py

@@ -3,7 +3,9 @@
 SET_TEMPLATE = """
 @micropython.viper
 def set{off}(dest: ptr32):
+    saved = dest
     dest[{off}] = {val}
+    assert int(saved) == int(dest)
 set{off}(buffer)
 print(hex(get_index(buffer, {off})))
 """
@@ -15,7 +17,9 @@ MASK = (1 << (8 * SIZE)) - 1
 
 @micropython.viper
 def set_index(dest: ptr32, i: int, val: uint):
+    saved = dest
     dest[i] = val
+    assert int(saved) == int(dest)
 
 
 def get_index(src, i):

tests/micropython/viper_ptr8_store_boundary_intbig.py

@@ -3,7 +3,9 @@
 SET_TEMPLATE = """
 @micropython.viper
 def set{off}(dest: ptr8):
+    saved = dest
     dest[{off}] = {val}
+    assert int(saved) == int(dest)
 set{off}(buffer)
 print(hex(get_index(buffer, {off})))
 """
@@ -15,7 +17,9 @@ MASK = (1 << (8 * SIZE)) - 1
 
 @micropython.viper
 def set_index(dest: ptr8, i: int, val: uint):
+    saved = dest
     dest[i] = val
+    assert int(dest) == int(saved)
 
 
 def get_index(src: ptr8, i: int):