gcc 4.1.0 (and 4.2-20050415) produces wrong output for this program.
I can reproduce it on i386 and mips/mipsel.
Calls for foo_read() must not be discarded (for example, 'mem' might point a
memory-mapped IO register),
but gcc -O optimizes a foo_read() call away.
gcc -O -fno-unit-at-a-time produces correct output.
static inline int inline_read(volatile int *mem)
{
return *mem;
}
int foo_read(volatile int *mem)
{
return inline_read(mem);
}
unsigned int foo(volatile int *mem)
{
foo_read(mem);
return foo_read(mem);
}
gcc -O output:
.file "foo.c"
.text
.globl foo_read
.type foo_read, @function
foo_read:
pushl %ebp
movl %esp, %ebp
movl 8(%ebp), %eax
movl (%eax), %eax
popl %ebp
ret
.size foo_read, .-foo_read
.globl foo
.type foo, @function
foo:
pushl %ebp
movl %esp, %ebp
subl $4, %esp
movl 8(%ebp), %eax
movl %eax, (%esp)
call foo_read
leave
ret
.size foo, .-foo
.ident "GCC: (GNU) 4.1.0"
.section .note.GNU-stack,"",@progbits
gcc -O -fno-unit-at-a-time output:
.file "foo.c"
.text
.globl foo_read
.type foo_read, @function
foo_read:
pushl %ebp
movl %esp, %ebp
movl 8(%ebp), %eax
movl (%eax), %eax
popl %ebp
ret
.size foo_read, .-foo_read
.globl foo
.type foo, @function
foo:
pushl %ebp
movl %esp, %ebp
pushl %ebx
subl $4, %esp
movl 8(%ebp), %ebx
movl %ebx, (%esp)
call foo_read
movl %ebx, (%esp)
call foo_read
addl $4, %esp
popl %ebx
popl %ebp
ret
.size foo, .-foo
.ident "GCC: (GNU) 4.1.0"
.section .note.GNU-stack,"",@progbits
--
Summary: a call for function with side-effects discarded by
optimization
Product: gcc
Version: 4.2.0
Status: UNCONFIRMED
Severity: critical
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: anemo at mba dot ocn dot ne dot jp
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27236
