http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54315
Bug #: 54315
Summary: Unnecessary copy of return value
Classification: Unclassified
Product: gcc
Version: 4.7.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected], [email protected]
On Linux/x86-64, I got
[hjl@gnu-6 pr20020]$ cat x.i
union S160
{
long double a;
};
extern union S160 check160 (void);
extern void checkx160 (union S160);
void
test160 (void)
{
checkx160 (check160 ());
}
[hjl@gnu-6 pr20020]$ gcc -S -O2 x.i
[hjl@gnu-6 pr20020]$ cat x.s
.file "x.i"
.text
.p2align 4,,15
.globl test160
.type test160, @function
test160:
.LFB0:
.cfi_startproc
subq $72, %rsp
.cfi_def_cfa_offset 80
call check160
fstpt 16(%rsp)
movq 16(%rsp), %rdx
movq 24(%rsp), %rax
movq %rdx, 32(%rsp)
movq %rax, 40(%rsp)
movq %rdx, (%rsp)
movq %rax, 8(%rsp)
call checkx160
addq $72, %rsp
.cfi_def_cfa_offset 8
ret
.cfi_endproc
.LFE0:
.size test160, .-test160
.ident "GCC: (GNU) 4.7.1 20120629 (Red Hat 4.7.1-1)"
.section .note.GNU-stack,"",@progbits
[hjl@gnu-6 pr20020]$ cat y.i
struct S160
{
long double a;
};
extern struct S160 check160 (void);
extern void checkx160 (struct S160);
void
test160 (void)
{
checkx160 (check160 ());
}
[hjl@gnu-6 pr20020]$ gcc -S -O2 y.i
[hjl@gnu-6 pr20020]$ cat y.s
.file "y.i"
.text
.p2align 4,,15
.globl test160
.type test160, @function
test160:
.LFB0:
.cfi_startproc
subq $24, %rsp
.cfi_def_cfa_offset 32
call check160
fstpt (%rsp)
call checkx160
addq $24, %rsp
.cfi_def_cfa_offset 8
ret
.cfi_endproc
.LFE0:
.size test160, .-test160
.ident "GCC: (GNU) 4.7.1 20120629 (Red Hat 4.7.1-1)"
.section .note.GNU-stack,"",@progbits
[hjl@gnu-6 pr20020]$
union causes unnecessary copy of return value. I don't believe
ABI calls for it.
