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RENESAS TOOL NEWS on February 16, 2006: RSO-M3T-NC30WA-060216D
A Note on Using the C Compiler Package
M3T-NC30WA |
Please take note of the following problem in using the C compiler package M3T-NC30WA, which is used for the M16C/60, M16C/30, M16C/20, M16C/10, M16C/Tiny, and R8C/Tiny series of MCUs:
- On comparing a constant with the return value from a function in an if statement
- Versions Concerned
M3T-NC30WA V.5.10 Release 1--V.5.40 Release 00
- Description
When the controlling expression of an if statement consists of a comparison of a constant with the return value from a function, and the substatement is an expression for assigning a constant to a variable, incorrect code may be generated for the assignment.
| 2.1 |
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Conditions
This problem occurs if the following conditions are all satisfied:
| (1) |
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Any one of the following optimizing options is selected:
-O1, -O2, -O3, -O4, -O5, -OR, and -OS |
| (2) |
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In the program exists an if statement that has no else statement. |
| (3) |
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The controlling expression of the if statement in (2) consists of a comparison of a constant with the return value from a function. |
| (4) |
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An equality (==) or inequality (!=) operator is used for the comparison in (3). |
| (5) |
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The substatement of the if statement in (2) is only an expression for assigning a constant to a variable. |
| (6) |
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The variable in (5) is any one of the following types:
unsigned char, signed char, unsigned int, and signed int |
| (7) |
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The variable in (5) is the return value from another function. |
| (8) |
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Another assignment expression same as the one described in (5) exists before the if statement in (2). |
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| 2.2 |
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Example
------------------------------------------------------------------
unsigned char sub(int);
inline unsigned char func( unsigned char c )
{
switch(c){
case 0:
c = 1; /* Condition (8) */
break;
case 1:
if ( sub(0) == 1 ){ /* Conditions (2), (3), and (4) */
c = 1; /* Conditions (5), (6), and (7) */
}
break;
default:
break;
}
return( c ); /* Condition (7) */
}
------------------------------------------------------------------ |
- Workaround
Place a dummy asm function immediately before the substatement of the if statement:
--------------------------------------------------------------------
. . . . . . . . . . .
if ( sub(0) == 1 ){
asm(""); /* Dummy asm function placed */
c = 1;
}
. . . . . . . . . . .
--------------------------------------------------------------------
- Schedule of Fixing the Problem
We plan to fix this problem in the next release of the product.
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