Using built-in specs.
Target: x86_64-redhat-linux-gnu
Configured with: ../gcc-4.0.3/configure x86_64-redhat-linux-gnu
--with-ld=/pixar/d2/sets/tools-03/bin/ld
--with-as=/pixar/d2/sets/tools-03/bin/as --prefix=/pixar/d2/sets/tools-03
--exec-prefix=/pixar/d2/sets/tools-03 --bindir=/pixar/d2/sets/tools-03/bin
--sbindir=/pixar/d2/sets/tools-03/sbin --sysconfdir=/pixar/d2/sets/tools-03/etc
--datadir=/pixar/d2/sets/tools-03/share
--includedir=/pixar/d2/sets/tools-03/include
--libdir=/pixar/d2/sets/tools-03/lib
--libexecdir=/pixar/d2/sets/tools-03/libexec
--localstatedir=/pixar/d2/sets/tools-03/var
--sharedstatedir=/pixar/d2/sets/tools-03/com
--mandir=/pixar/d2/sets/tools-03/man --infodir=/pixar/d2/sets/tools-03/info
--enable-version-specific-runtime-libs --enable-symvers
--enable-languages=c++,objc,f95 --enable-threads=posix --enable-shared
--enable-mudflap
Thread model: posix
gcc version 4.0.3
----------------------code----------------
struct Big {
char data[1024];
};
void ByValue(Big);
void MakeACopy() {
Big stuff;
ByValue(stuff);
}
-----------------------------------
The relevant assembly code, when compiled as: g++ -O2 -S prog.cpp
.globl _Z9MakeACopyv
.type _Z9MakeACopyv, @function
_Z9MakeACopyv:
.LFB2:
pushq %rbx
.LCFI0:
movl $1024, %edx
subq $3072, %rsp
.LCFI1:
leaq 2048(%rsp), %rbx
leaq 1024(%rsp), %rsi
movq %rbx, %rdi
call memcpy
movq %rbx, %rsi
movq %rsp, %rdi
movl $1024, %edx
call memcpy
call _Z7ByValue3Big
addq $3072, %rsp
popq %rbx
ret
-------------------
I'm far from an export, but it sure looks to me like memcpy is being called
twice to copy the data!
This is supported by the fact that gcc3.3.2 only emits code to copy it once,
and that code runs twice as fast.
Also, gcc3.3.2 inlines the memcpy, while gcc4.0.3 does not. I assume that's a
regression as well?
If not, what's the best option to tell gcc4.0.3 to inline the copy?
--
Summary: gcc4.0.3 produces code that copies a structure twice
Product: gcc
Version: 4.0.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: deb at pixar dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29375
