[Bug target/56807] mingw32: Conflict between stack realignment and stack probe destroys function argument in EAX

[BugMaster at narod dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56807

Anton Mitrofanov <BugMaster at narod dot ru> changed:

           What    |Removed                     |Added
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                 CC|                            |BugMaster at narod dot ru

--- Comment #18 from Anton Mitrofanov <BugMaster at narod dot ru> ---
This patch is ok for mingw32 target but may produce incorrect code for x86_64
linux target in case of saving/restoring both rax and r10. In that case during
restoring of rax register (in "if (r10_live && eax_live)" path of
http://gcc.gnu.org/viewcvs/gcc/trunk/gcc/config/i386/i386.c?r1=205860&r2=205859&pathrev=205860)
we will make move from incorrect address [rsp + allocate - UNITS_PER_WORD]
while the saved value will be at address [rsp + allocate + UNITS_PER_WORD].
Here is possible code that can be generated (by looking at current gcc source
code):

// suppose rsp == 1000 here
push rax // rsp == 992 ; [992] == rax
push r10 // rsp == 984 ; [984] == r10
mov rax, 400 // where 400 is allocate value
call allocate_stack
sub rsp, rax // rax == 400 so rsp == 584
mov r10, [rsp + 400] // 584 + 400 == 984 ; r10 = [984]
mov rax, [rsp + 400 - 8] // 584 + 400 - 8 == 976 ; rax = [976] <- WRONG

Instead the last instruction should be

mov rax, [rsp + 400 + 8] // 584 + 400 + 8 == 992 ; rax = [992]

Sorry, I can't write test case to trigger this code path so I will leave this
comment here and not create new bug report (if you want you can move it to new
bug report).