https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106991
Bug ID: 106991 Summary: new+delete pair not optimized by g++ at -O3 but optimized at -Os Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: hiraditya at msn dot com Target Milestone: --- https://godbolt.org/z/PeYcoqTKn ----------------------------------------------------------- #include<cassert> #include<cstdlib> int volatile gv = 0; void* operator new(long unsigned sz ) { ++gv; return malloc( sz ); } void operator delete(void *p) noexcept { --gv; free(p); } class c { int l; public: c() : l(0) {} int get(){ return l; } }; int caller( void ){ c *f = new c(); assert( f->get() == 0 ); delete f; return gv; } ----------------------------------------------------------- $ g++ -std=c++20 -O3 operator new(unsigned long): mov eax, DWORD PTR gv[rip] add eax, 1 mov DWORD PTR gv[rip], eax jmp malloc operator delete(void*): mov eax, DWORD PTR gv[rip] sub eax, 1 mov DWORD PTR gv[rip], eax jmp free caller(): sub rsp, 8 mov eax, DWORD PTR gv[rip] mov edi, 4 add eax, 1 mov DWORD PTR gv[rip], eax call malloc mov esi, 4 mov rdi, rax call operator delete(void*, unsigned long) mov eax, DWORD PTR gv[rip] add rsp, 8 ret gv: .zero 4 ----------------------------------------------------------- $ g++ -std=c++20 -Os operator new(unsigned long): mov eax, DWORD PTR gv[rip] inc eax mov DWORD PTR gv[rip], eax jmp malloc operator delete(void*): mov eax, DWORD PTR gv[rip] dec eax mov DWORD PTR gv[rip], eax jmp free caller(): mov eax, DWORD PTR gv[rip] ret gv: .zero 4