This is an automated cherry-pick of pingcap#3681

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>

dbms/src/Functions/FunctionsTiDBConversion.h

@@ -680,6 +680,8 @@ struct TiDBConvertToFloat
             context.getDAGContext()->handleTruncateError("Truncated incorrect DOUBLE value");
             return 0.0;
         }
+        if (float_string.size < trim_string.size())
+            trim_string[float_string.size] = '\0';
         Float64 f = strtod(float_string.data, nullptr);
         if (f == std::numeric_limits<Float64>::infinity())
         {

tests/fullstack-test/expr/cast_string_as_real.test

@@ -1,29 +1,35 @@
 mysql> drop table if exists test.t
 mysql> create table test.t(a char(30))
 mysql> alter table test.t set tiflash replica 1
-mysql> insert into test.t values ('1.23'),('123'),('-123.99'),('+123.123-'),(0),(0.0),(NULL),('1.11.00'),('11xx'),('11.xx'),('xx.11'),('1e649'),('-1e649'),('9.9999999999999999'),('9.999999999999999')
+mysql> insert into test.t values ('1.23'),('123'),('-123.99'),('+123.123-'),(0),(0.0),(NULL),('1.11.00'),('11xx'),('11.xx'),('xx.11'),('1e649'),('-1e649'),('9.9999999999999999'),('9.999999999999999');
+mysql> insert into test.t values ('0x01'),('-0x01'),('1x01'),('-1x01.2'),('0x01.2'),('x1');
 
 func> wait_table test t
 
-mysql> set tidb_allow_mpp=1; set tidb_isolation_read_engines='tiflash'; select a, b from (select a, cast(a as double) as b from test.t) t group by a, b order by a
+mysql> set tidb_enforce_mpp=1; set tidb_isolation_read_engines='tiflash'; select a, cast(a as double) b from test.t order by a;
 +--------------------+-------------------------+
 | a                  | b                       |
 +--------------------+-------------------------+
 | NULL               |                    NULL |
 | +123.123-          |                 123.123 |
+| -0x01              |                      -0 |
 | -123.99            |                 -123.99 |
 | -1e649             | -1.7976931348623157e308 |
+| -1x01.2            |                      -1 |
 | 0                  |                       0 |
 | 0.0                |                       0 |
+| 0x01               |                       0 |
+| 0x01.2             |                       0 |
 | 1.11.00            |                    1.11 |
 | 1.23               |                    1.23 |
 | 11.xx              |                      11 |
 | 11xx               |                      11 |
 | 123                |                     123 |
 | 1e649              |  1.7976931348623157e308 |
+| 1x01               |                       1 |
 | 9.999999999999999  |       9.999999999999998 |
 | 9.9999999999999999 |                      10 |
+| x1                 |                       0 |
 | xx.11              |                       0 |
 +--------------------+-------------------------+
 
-mysql> drop table if exists test.t

tests/fullstack-test/expr/issue_3447.test

@@ -0,0 +1,14 @@
+mysql> drop table if exists test.t;
+mysql> create table test.t(a char(5));
+mysql> alter table test.t set tiflash replica 1;
+mysql> insert into test.t values ('0.1'), ('-0.1'), ('0.0'), ('-1'), ('a0.1'), ('0x01');
+
+func> wait_table test t
+mysql> select /*+ read_from_storage(tiflash[t]) */ * from test.t where a;
++------+
+| a    |
++------+
+| 0.1  |
+| -0.1 |
+| -1   |
++------+