On a i686 platform, the example below is miscompiled with -O1.
I expect this program to print -0.96. Here's what it actually does:
$ g++ -O1 -o y y.cc
$ ./y
-1.288766
$ g++ -o y y.cc
$ ./y
-0.960000
$
The value that the optimized version prints is actually different
on each run of the program.
Here's the generated code for main(),
.globl main
.type main, @function
main:
pushl %ebp
movl %esp, %ebp
subl $24, %esp
movl %ebx, -8(%ebp)
movl %esi, -4(%ebp)
andl $-16, %esp
subl $16, %esp
movl $0, 12(%esp)
movl 8(%esp), %ebx ; this seems to load ebx with garbage???
movl 12(%esp), %esi
fldz
fstl 8(%esp)
fstpl (%esp)
call _Z8x_from_zdd
fstpl 4(%esp)
movl %ebx, 8(%esp) ; this clobbers half of the arg with
; the garbage
movl %esi, 12(%esp)
movl $0, (%esp)
call _Z17local_to_trflocalidi
movl $0, %eax
movl -8(%ebp), %ebx
movl -4(%ebp), %esi
movl %ebp, %esp
popl %ebp
ret
It looks to me like the error occurs during RTL generation.
Here's the tree dump from the t87.final_cleanup file (slightly trimmed):
void local_to_trflocal(int, double, int) (D.1741, x_loc, D.1743)
{
<bb 0>:
printf (&"%f\n"[0], x_loc);
return;
}
double x_from_z(double, double) (pitch, stereo)
{
<bb 0>:
return -9.59999999999999964472863211994990706443786621094e-1 / cos (stereo);
}
int main() ()
{
<bb 0>:
local_to_trflocal (0, x_from_z (0.0, 0.0), 0);
return 0;
}
But in the 00.expand file, here's the sequence leading
to the local_to_trflocal() call:
(insn 27 26 28 1 (set (mem/i:DF (plus:SI (reg/f:SI 56 virtual-outgoing-args)
(const_int 4 [0x4])) [0 S8 A32])
(reg:DF 71)) -1 (nil)
(nil))
(insn 28 27 29 1 (set (mem:DI (plus:SI (reg/f:SI 56 virtual-outgoing-args)
(const_int 8 [0x8])) [0 S8 A8])
(reg:DI 68)) -1 (nil)
(nil))
(insn 29 28 30 1 (set (mem:SI (reg/f:SI 56 virtual-outgoing-args) [0 S4 A32])
(const_int 0 [0x0])) -1 (nil)
(nil))
(call_insn 30 29 31 1 (call (mem:QI (symbol_ref:SI ("_Z17local_to_trflocalidi")
[flags 0x3] <function_decl 0xb7f0df80 local_to_trflocal>) [0 S1 A8])
(const_int 16 [0x10])) -1 (nil)
(nil)
(nil))
Reg 71 here is the return value from x_from_z.
I don't know where the DI store to v-o-a+8 is coming from...
Environment:
System: Linux karma 2.6.12.1sss #2 Thu Jul 7 00:28:21 EDT 2005 i686 i686 i386
GNU/Linux
Architecture: i686
<machine, os, target, libraries (multiple lines)>
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: /home/sss/gcc/gcc/configure --prefix=/usr/local/gcc
--enable-threads=posix --enable-long-long --enable-languages=c,c++,f95
How-To-Repeat:
Compile with -O1
-----------------------------------------------------
//g++ -O1 -g -o y y.cc
extern "C" double cos(double);
extern "C" int printf (...);
double x_from_z(double pitch=0, double stereo=0)
{
return -0.96/cos(stereo);
}
void local_to_trflocal(int, double x_loc, int=0)
{
printf ("%f\n", x_loc);
}
int main()
{
local_to_trflocal(0, x_from_z());
return 0;
}
-----------------------------------------------------
------- Additional Comments From snyder at fnal dot gov 2005-09-08 02:31
-------
Fix:
<how to correct or work around the problem, if known (multiple lines)>
--
Summary: 4.1: wrong code in argument passing
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: snyder at fnal dot gov
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23775
