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MAEC TOOL NEWS:
MAECT-M3T-NC30WA-020801D
Notes on C Compiler
M3T-NC30WA V.5.00 Release 1
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Please take note of the following problems in using C compiler (with an assembler and integrated development environment) M3T-NC30WA V.5.00 Release 1 for the M16C/60, M16C/30, M16C/20, and M16C/10 series MCUs:
- On two successive if constructs with the same conditional expression
- On incorrectly deleting codes in selection statements such as if statements by optimization
- Problem on Two Successive if Constructs with the Same Conditional Expression
- 1.1 Description
- When two if constructs with the same conditional expression are described in succession, "System Error" may arise or incorrect codes be generated.
- 1.2 Conditions
- This problem occurs if the following seven conditions are satisfied:
| (1) |
Any one or more of optimizing options -O, -O[3-5], -OR, and -OS are used, and -ONBSD (-Ono_break_source_debug) is not selected. |
| (2) |
Two if constructs with the same conditional expression are described in succession, and between them is described nothing. The first if construct is called if construct A and the second is if construct B, hereafter. |
| (3) |
The variable used in the conditional expression in (2) is an auto variable or an argument to a function. |
| (4) |
An if statement exists at the end of the program statement in if construct A. |
| (5) |
An if statement exists at the beginning of the program statement in if construct B. |
| (6) |
The variable used at the beginning of the conditional expression of the if statement in (5) is also used in the conditional expression of the if statement in (4). |
| (7) | The variable in (6) meets all the following conditions:
It is a global or static variable.
It is not declared using the volatile qualifier.
Its type is any one of the following:
_Bool,
signed char, unsigned char,
signed int, unsigned int,
signed short, unsigned short,
signed long, and unsigned long
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- 1.3 Example
-----------------------------------------------------------------------
int gi1; /* Condition (7) */
int gi2;
char gc;
void func(void)
{
int ac = gc + 2;
- if(ac){ /* Conditions (2) and (3) */
| :
| if(gi2 == 7 && gi1 == 6){ /* Conditions (4) and (6) */
A gi1 = 3;
| }
| }
- /* Condition (2) */
- if(ac){ /* Conditions (2) and (3) */
| if(gi1 == 5 && gi2 == 8){ /* Conditions (5) and (6) */
| gi1 = 5;
B }
| :
| }
-
}
-----------------------------------------------------------------------
- 1.4 Workaround
- This problem will be circumvented in either of the following ways:
- (1) Place a dummy asm function between two if constructs in Condition (2) above.
- (2) Compile the program using optimizing option -ONBSD (-Ono_break_source_debug).
[Example]
-----------------------------------------------------------------------
int gi1;
int gi2;
char gc;
void func(void)
{
int ac = gc + 2;
- if(ac){
| :
| if(gi2 == 7 && gi1 == 6){
A gi1 = 3;
| }
| }
-
asm(); /* A dummy asm function placed */
- if(ac){
| if(gi1 == 5 && gi2 == 8){
| gi1 = 5;
B }
| :
| }
-
}
-----------------------------------------------------------------------
- 1.5 Schedule of Fixing the Problem
- We plan to fix this problem in our next release.
Notes on C Compiler M3T-NC30WA V.5.00 Release 1
MAECT-M3T-NC30WA-020801D
- Problem on Incorrectly Deleting Codes in Selection Statements Such as if Statements by Optimization
- 2.1 Description
- When compiling an if-else construct using optimizing options, codes for the selection statements of the if-else construct may be deleted incorrectly.
- 2.2 Conditions
- This problem occurs if the following seven conditions are satisfied:
| (1) |
Any one or more of optimizing options -O, -O[1-5], -OR, and -OS are used. |
| (2) | An if-else construct exists. |
| (3) |
After the if-else construct in (2) is described another selection statement (including a switch statement) or an iteration statement (for, while, or do-while), and an auto variable is used in its conditional expression. |
| (4) |
One or more conditional expressions exist in either of the if and the else statement involved in the if-else construct in (2) above. |
| (5) |
The assignment expressions to the same auto variable exist in both of the if and the else statement involved in the if-else construct in (2) above, and the assignment expression(s) in either of the if and the else statement is executed according to the evaluation of the conditional expression(s) in (4). |
| (6) |
The assignment expressions in (5) make the results of evaluation of the conditional expression in (3) be the same value. |
| (7) |
Between the if-else construct in (2) and the selection or iteration statement in (3) exists no statement for referencing the auto variable in (5). |
- 2.3 Examples
[Example 1]
-----------------------------------------------------------------------
void func(void) {
int k; /* Condition (5) */
k = 0;
- if(i == 0){
| k = 1; /* Conditions (5) and (6) */
| }else{
| if(j == 0){ /* Condition (4) */
(2) k = 1; /* Conditions (5) and (6) */
| }
| if(j == 1){ /* Condition (4) */
| k = 1; /* Conditions (5) and (6) */
| }
- }
/* Condition (7) */
- if(k == 1) /* Condition (3) */
| gi++;
(3) :
| :
- }
-----------------------------------------------------------------------
[Example 2]
-----------------------------------------------------------------------
void func(void) {
int k; /* Condition (5) */
k = 0;
- if(i == 0){
| k = 1; /* Conditions (5) and (6) */
| }else{
| switch(j){ /* Condition (4) */
| case 0:
| case 1:
(2) k = 1; /* Conditions (5) and (6) */
| break;
| }
| if(j == 1){ /* Condition (4) */
| k = 1; /* Conditions (5) and (6) */
| }
- }
/* Condition (7) */
- if(k == 1) { /* Condition (3) */
| gi++;
(3) :
| :
- }
-----------------------------------------------------------------------
- In the source files shown in examples 1 and 2, codes generated by compiling the conditional expression in Condition (3) will be deleted.
The reason is that even if immediate value 1 is not assigned to variable k in the if-else construct in Condition (2), M3T-NC30WA interprets the value of variable k in the conditional expression in Condition (3) as immediate value 1; as a result, codes are incorrectly deleted.
- 2.4 Workaround
- Place a dummy asm function immediately before the conditional expression involved in the deletion.
-----------------------------------------------------------------------
void func(void) {
int k;
k = 0;
if(i == 0){
k = 1;
}else{
if(j == 0){
k = 1;
}
if(j == 1){
k = 1;
}
}
asm(); /* A dummy asm function placed */
if(k == 1)
gi++;
}
-----------------------------------------------------------------------
- 2.5 Schedule of Fixing the Problem
- We plan to fix this problem in our next release.
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