Epson S5U1C17001C Manual page 370

6 C COMPilEr
Code is compiled unchanged, generating unnecessary code as well, including code that assigns
values to local variables that are never referenced. While the values of the variables loaded in
registers will not be reused, local variables that are declared as registered will be optimized
and deleted, as needed.
-O/-O1
Code size and execution speed optimized
The optimization performed here includes the following processes:
Unnecessary code is deleted (e.g., code that assigns a value to a never-referenced local
variable).
Variable processing is assigned with a register, and the value of this register is reused to reduce
memory read/write counts. However, since this removes guaranteed memory access, variables
that require fail-proof read/writes to memory must be declared as volatile.
Loop process optimization is performed. Optimization based on predicting branch conditions
prevents repetition of duplicate compare instructions.
-O3
This setting optimizes code execution speed more effectively than the -O option, resulting in
the following differences with respect to the -O option:
Common computation processes in the global region are replaced by single computation
(common equations in the global region are deleted). Loop process optimization is performed
twice.
Register allocation is optimized for operands for simple commands (e.g., Id).
Branch condition blocks without attainable destinations are ignored; no code is generated.
Functions lacking inline declarations are expanded inline. The subroutine of a simple code
copies the code of the function itself rather than calling a function, eliminating the overhead
associated with a function call.
Depending on the source code, the -O3 option may not result in the fastest execution speed in
certain cases.
Avoid using the -O2 or -Os options, which are not supported.
Default: Code optimization is performed.
-gstabs
Add debugging information with relative path to source files
Function:
Description: This option is used to creates an output file containing debugging information.
The source file location information is output as a relative path. The basic make file generated by
the IDE specifies this option when invoking the xgcc C compiler.
Default: No debugging information is output.
-fno-builtin
Disable built-in functions
Function:
Description: The functions listed below are always called, not compiled as built-in functions. If this option is
not specified, the compiler will expand the following functions inline or replace them with other
functions make code generation more efficient, depending on circumstances.
abort, abs, cos, exit, exp, fabs, fprintf, fputs, labs, log, memcmp, memcpy,
memset, printf, putchar, puts, scanf, sin, sprintf, sqrt, sscanf, strcat,
strchr, strcmp, strcpy, strcspn, strlen, strncat, strncmp, strncpy,
strpbrk, strrchr, strspn, strstr, vprintf, vsprintf
Default: The built-in functions are enabled.
-mpointer16
Generate code for 16-bit (64KB) data space
Function:
Description: This option is used to generate codes that use 16-bit data pointers (the data space is limited up to
64KB).
This option allows the user program to reduce the RAM size for storing static variable pointers.
However, the stack size cannot be reduced by this option.
Default: The C compiler generates the object that allows data to be located in the 24-bit (16MB) space.
-mshort-offset
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