https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62117
Bug ID: 62117
Summary: [4.9 regression] wrong code for passing small array
argument'Address, in generic
Product: gcc
Version: 4.9.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ada
Assignee: unassigned at gcc dot gnu.org
Reporter: demoonlit at panathenaia dot halfmoon.jp
Created attachment 33306
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33306&action=edit
minimal bug triggering source code
When instantiating a generic function like below, with a small array type
placed in register, according to x86_64 System V calling convension,
generic
type Key_Type is limited private;
function Compare (Left, Right : Key_Type) return Integer;
'Address attributes of arguments point wrong place.
The compiler probably has forgotten to store the arguments to memory.
For example, if the body calls memcmp,
function Compare (Left, Right : Key_Type) return Integer is
begin
return memcmp (Left'Address, Right'Address, Key_Type'Size / 8);
end Compare;
The generated code compiled with -S -Og:
==== gcc-4.9 ====
_inst__compare:
LFB1:
subq $40, %rsp
LCFI0:
movq %rsp, %rsi # Left and Right are passed by %rdi and %rsi
leaq 16(%rsp), %rdi # but this generated code overwrites them
movl $4, %edx
call _memcmp
addq $40, %rsp
LCFI1:
ret
This bug has appeared from gcc-4.9. gcc-4.8 is ok.
=== gcc-4.8 ====
_inst__compare:
LFB1:
subq $40, %rsp
LCFI0:
movl %edi, 16(%rsp) # Left and Right are stored on the stack
movl %esi, (%rsp)
movq %rsp, %rsi
leaq 16(%rsp), %rdi
movl $4, %edx
call _memcmp
addq $40, %rsp
LCFI1:
ret
