[Bug tree-optimization/60973] New: Invalid propagation of a tail call in copyrename2 pass
ubizjak at gmail dot com
gcc-bugzilla@gcc.gnu.org
Sat Apr 26 08:27:00 GMT 2014
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60973
Bug ID: 60973
Summary: Invalid propagation of a tail call in copyrename2 pass
Product: gcc
Version: 4.10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: ubizjak at gmail dot com
This problem can be illustrated with a target, that doesn't define
TARGET_ASM_CAN_OUTPUT_MI_THUNK, such as h8300-elf.
Compiling g++.dg/ipa/imm-devirt-2.C using -O2 with a crosscompiler to
h8300-elf, we get in _.037t.inline_param2:
virtual int C::_ZThn10_N1C3fooEi(int) (struct C * const this, int i)
{
int retval___0;
<bb 2>:
this_2 = this_1(D) + 65526;
retval___0_5 = C::foo (this_2, i_4(D)); [tail call]
return retval___0_5;
}
and
int main(int, char**) (int argc, char * * argv)
{
struct C c;
int _3;
int _6;
<bb 2>:
C::C (&c);
_3 = get_input ();
_6 = C::_ZThn10_N1C3fooEi (&c.D.1912.D.1895, _3);
if (_6 != 4)
goto <bb 3>;
else
goto <bb 4>;
<bb 3>:
abort ();
<bb 4>:
c ={v} {CLOBBER};
return 0;
}
However, copyrename2 pass propagates tail call annotation to the call site,
resulting in _.054t.copyrename2:
int main(int, char**) (int argc, char * * argv)
{
int retval___0;
int D.2161;
struct C * const this;
struct C c;
int _3;
int _6;
<bb 2>:
C::C (&c);
_3 = get_input ();
this_7 = &c.D.1912.D.1895 + 65526;
retval___0_8 = C::foo (this_7, _3); [tail call] <<< here!
_9 = retval___0_8;
_6 = _9;
if (_6 != 4)
goto <bb 3>;
else
goto <bb 4>;
<bb 3>:
abort ();
<bb 4>:
c ={v} {CLOBBER};
return 0;
}
On a target that support sibcalls, RTL expansion ends after tail call, so
_.170r.expand ends with:
...
(call_insn/u/j 15 14 16 2 (set (reg:SI 3 r3)
(call (mem:SI (symbol_ref:SI ("_ZN1C3fooEi") [flags 0x3]
<function_decl 0x7fe46eeab200 foo>) [0 foo S4 A32])
(const_int 0 [0]))) -1
(expr_list:REG_EH_REGION (const_int 0 [0])
(nil))
(expr_list:SI (use (reg:SI 4 r4))
(expr_list:SI (use (reg:SI 3 r3))
(nil))))
;; succ: EXIT [100.0%] (ABNORMAL,SIBCALL)
(barrier 16 15 0)
The tail call is valid only in _ZThn16_N1C3fooEi (a.k.a non-virtual thunk to
C::foo(int)) and should not be propagated as a tail call to its call site.
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