I noticed a optimization difference between compiling a simple source code with ARM GCC in C and C++. The C++ version seems to optimize a lot less stack usage.
To demonstrate this problem, I compiled the following code with arm-none-eabi-gcc version gcc-arm-none-eabi-8-2018-q4-major-win32, first only -O2, then with -O2 -x c++ :
#include <stdio.h> #include <stdint.h> struct TestStruct { uint32_t field1; uint32_t field2; uint32_t field3; uint32_t field4; } ; struct TestStruct initStructure(uint32_t f1, uint32_t f2, uint32_t f3, uint32_t f4) { struct TestStruct myStruct; myStruct.field1 = f1; myStruct.field2 = f2; myStruct.field3 = f3; myStruct.field4 = f4; printf("Temp Address %lx", &myStruct); return myStruct; } void doStuff(struct TestStruct myStruct) { printf("f1 = %d, f2 = %d, f3 = %d, f4 = %d", myStruct.field1, myStruct.field2, myStruct.field3, myStruct.field4); } int main(void) { doStuff(initStructure(1,2,3,4)); doStuff(initStructure(11,22,33,44)); doStuff(initStructure(11,12,13,14)); doStuff(initStructure(21,22,23,24)); }
Here are link to demonstrate the problem :
https://godbolt.org/z/PGCp2y Pure C
Line 44, stack usage is
https://godbolt.org/z/7XfsQR C++
Line 37, stack usage is