8051 What does SDCC do part 1 ?

1. Introduction and Problem Statement A good way to learn what a compiler really does when transforming a C source code into a binary is to disassemble the binary and compare it with the C source code. It is especially true for 8 bits microcontrollers like the 8051. In order to test SDCC we are going to use the following C source code. /* ========================================================================== * * Universal Test Corpus - Heterogeneous Architecture Analysis * * ========================================================================== */ #include <stdint.h> // 1. Global variables (testing absolute/relative addressing modes) volatile uint32_t global_var_32 = 0xDEADBEEF ; volatile uint8_t global_var_8 = 0x42 ; const char string_const [] = "TARGET_STRING" ; // 2. Function with parameter passing and local variables (stack / Frame Pointer test) int32_t callee_function ( int16_t a , int16_t b ) { volatile int32_t local_result = 0 ; // Basic and mixed arithmetic operations (8, 16, 32 bits) local_result += ( int32_t )( a * b ); local_result -= ( int32_t )( a / ( b | 1 )); // Avoid division by zero // Shift tests and logical operations (highly variable depending on ISAs) local_result = ( local_result << 2 ) ^ 0x55AA55AA ; local_result = ( local_result >> 1 ) | ( int32_t ) global_var_8 ; return local_result ; } // 3. Main function grouping complex control flows int main ( void ) { volatile int32_t accumulator = 0 ; int16_t i ; // Loop test (Conditional jumps, decrement, comparison tests) for ( i = 0 ; i < 10 ; i ++ ) { if ( i == 5 ) { accumulator += 100 ; } else { accumulator += i ; } } // Multiple branching test (Switch / Jump Table or cascaded if-else) switch ( global_var_8 ) { case 0x10 : accumulator += 10 ; break ; case 0x20 : accumulator += 20 ; break ; default: accumulator -= 5 ; break ; } // Function call (Stack management, save registers Link Register/PC) accumulator += callee_function (( int16_t ) accumulator , 3 ); // Pointer and indirect memory ac