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Hello,
Ran into it while compiling Lazarus. It appears that, while many
sophisticated checks are done in tcallnode.maybe_create_funcret_node,
the obvious case when function result destination is one of the
function's arguments, is not checked. To be honest, I noticed that
earlier for the case of s := Copy(s, ...), but was thiniking that there
is some compiler magic around Copy(). Delphi also appears to be smart
enough to omit temps in case of s := copy(s,...).
Anyway, since copy() assigns its result once before exiting, it works
fine. Things go wrong when the function is tries to access its argument
after modifying the result, like in the attached example.
This issue is caused by your own patch to change the ansistring code to use pass the result by reference.
Original code (using current 2.2.1) was:
# [21] s := foo(s); // This one failes movl -4(%ebp),%eax
call P$PROGRAM_FOO$ANSISTRING$$ANSISTRING
movl %eax,%ebx
leal -4(%ebp),%eax
call FPC_ANSISTR_DECR_REF
movl %ebx,-4(%ebp)
The new code since r9718 is:
# [21] s := foo(s); // This one failes leal -4(%ebp),%edx
movl -4(%ebp),%eax
call P$PROGRAM_FOO$ANSISTRING$$ANSISTRING
Here you can see that the result is at the same location as the parameter. In the original code the value is only assigned to the original location after the call.
The quick-solution is simple: revert r9718 until it works.
Peter