You appear to be correct. Clang does not devirtualize in LTO, but GCC does. Personally I consider this very strange. $ cat animal.h cat.cpp main.cpp /

You appear to be correct. Clang does not devirtualize in LTO, but GCC does. Personally I consider this very strange. $ cat animal.h cat.cpp main.cpp // animal.h #pragma once class animal { public: virtual ~animal() {} virtual void speak() = 0; }; animal& get_mystery_animal(); // cat.cpp #include "animal.h" #include <cstdio> class cat final : public animal { public: ~cat() override{} void speak() override{ puts("meow"); } }; static cat garfield{}; animal& get_mystery_animal() { return garfield; } // main.cpp #include "animal.h" int main() { animal& a = get_mystery_animal(); a.speak(); } $ make clean && CXX=clang++ make -j && objdump --disassemble=main -C lto_test rm -f *.o lto_test clang++ -c -flto -O3 -g cat.cpp -o cat.o clang++ -c -flto -O3 -g main.cpp -o main.o clang++ -flto -O3 -g cat.o main.o -o lto_test lto_test: file format elf64-x86-64 Disassembly of section .init: Disassembly of section .plt: Disassembly of section .plt.got: Disassembly of section .text: 00000000000011b0 <main>: 11b0: 50 push %rax 11b1: 48 8b 05 58 2e 00 00 mov 0x2e58(%rip),%rax # 4010 <garfield> 11b8: 48 8d 3d 51 2e 00 00 lea 0x2e51(%rip),%rdi # 4010 <garfield> 11bf: ff 50 10 call *0x10(%rax) 11c2: 31 c0 xor %eax,%eax 11c4: 59 pop %rcx 11c5: c3 ret Disassembly of section .fini: $ make clean && CXX=g++ make -j && objdump --disassemble=main -C lto_test|sed -e 's,^, ,' rm -f *.o lto_test g++ -c -flto -O3 -g cat.cpp -o cat.o g++ -c -flto -O3 -g main.cpp -o main.o g++ -flto -O3 -g cat.o main.o -o lto_test lto_test: file format elf64-x86-64 Disassembly of section .init: Disassembly of section .plt: Disassembly of section .plt.got: Disassembly of section .text: 0000000000001090 <main>: 1090: 48 83 ec 08 sub $0x8,%rsp 1094: 48 8d 3d 75 2f 00 00 lea 0x2f75(%rip),%rdi # 4010 <garfield> 109b: e8 50 01 00 00 call 11f0 <cat::speak()> 10a0: 31 c0 xor %eax,%eax 10a2: 48 83 c4 08 add $0x8,%rsp 10a6: c3 ret Disassembly of section .fini: