Bug 19384 – [Codegen] Address of stack temporary is returned

opIndex function returns address of stack local temporary instead of this Reduced code: --- void main() { Vec preds = Vec(0xDEAD); void* ptr1 = &preds; void* ptr2 = &preds[0]; assert(ptr1 == ptr2); } struct Vec { uint item; ref uint opIndex(size_t index) { return item; // commenting next line removes bug foreach(ref val; range()) return val; assert(false); } } struct range { int opApply(scope int delegate(ref uint) dg) { return 0; } } --- Assembly without comment: --- ref uint opIndex(size_t index) push rbp mov rbp,rsp sub rsp,30h mov qword ptr [this],rcx mov qword ptr [index],rdx { return item; mov rax,qword ptr [this] mov qword ptr [__result],rax mov qword ptr [rbp-28h],rax // result is stored on stack lea rax,[rbp-28h] // address of stack is returned instead of value from stack // commenting next line fixes bug foreach(ref val; range()) return val; assert(false); } mov rsp,rbp pop rbp ret --- Assembly with comment: --- ref uint opIndex(size_t index) push rbp mov rbp,rsp mov qword ptr [this],rcx mov qword ptr [index],rdx { return item; mov rax,qword ptr [this] // commenting next line fixes bug //foreach(ref val; range()) return val; assert(false); } pop rbp ret --- Tested on windows and on linux (https://run.dlang.io/is/7dqb1T)

This problem happens on 32 bit code, too. Slightly reduced test case: void main() { Vec preds = Vec(0xDEAD); void* ptr2 = &preds.august(); assert(&preds == ptr2); } struct Vec { uint item; ref uint august() { return item; // commenting next line removes bug foreach(ref val; range()) return val; assert(false); } } struct range { int opApply(scope int delegate(ref uint) dg) { return 0; } }

Replace the `ref uint` return with a `uint*` pointer and it works. So, the problem must be in the logic that treats a pointer return, but not a ref return.

@WalterBright created dlang/dmd pull request #11701 "fix Issue 19384 - [Codegen] Address of stack temporary is returned" fixing this issue: - fix Issue 19384 - [Codegen] Address of stack temporary is returned https://github.com/dlang/dmd/pull/11701

dlang/dmd pull request #11701 "fix Issue 19384 - [Codegen] Address of stack temporary is returned" was merged into master: - d8d294f38676f98bedef7d069746532e6f6c2c64 by Walter Bright: fix Issue 19384 - [Codegen] Address of stack temporary is returned https://github.com/dlang/dmd/pull/11701