http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56124
Bug #: 56124
Summary: Redundant reload for loading from memory
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: amker.ch...@gmail.com
For below test case:
typedef __builtin_va_list __gnuc_va_list;
typedef __gnuc_va_list va_list;
struct _reent
{
int _stdout;
};
struct _reent *_impure_ptr;
int bar (struct _reent *, int, const char *, va_list);
int
foo(const char *fmt , ...)
{
int ret;
va_list ap;
struct _reent *ptr = _impure_ptr;
__builtin_va_start(ap,fmt);
ret = bar (ptr, ((ptr)->_stdout), fmt, ap);
__builtin_va_end(ap);
return ret;
}
The dump of reload pass is:
1: NOTE_INSN_DELETED
4: NOTE_INSN_BASIC_BLOCK 2
28: r3:SI=sp:SI+0x10
REG_EQUAL sp:SI+0x10
2: r2:SI=[r3:SI++]
REG_INC r3:SI
REG_EQUIV [afp:SI]
31: [sp:SI+0x10]=r2:SI
3: NOTE_INSN_FUNCTION_BEG
6: r2:SI=[`*.LC0']
REG_EQUIV `_impure_ptr'
7: r0:SI=[r2:SI]
9: [sp:SI+0x4]=r3:SI
10: r1:SI=[r0:SI]
14: r2:SI=[sp:SI+0x10]
16: r0:SI=call [`bar'] argc:0
25: use r0:SI
29: NOTE_INSN_DELETED
which could be:
1: NOTE_INSN_DELETED
4: NOTE_INSN_BASIC_BLOCK 2
28: r3:SI=sp:SI+0x10
REG_EQUAL sp:SI+0x10
2: r2:SI=[r3:SI++]
REG_INC r3:SI
REG_EQUIV [afp:SI]
3: NOTE_INSN_FUNCTION_BEG
6: r1:SI=[`*.LC0']
REG_EQUIV `_impure_ptr'
7: r0:SI=[r1:SI]
9: [sp:SI+0x4]=r3:SI
10: r1:SI=[r0:SI]
16: r0:SI=call [`bar'] argc:0
25: use r0:SI
29: NOTE_INSN_DELETED
It is obvious that insn 31/14 are generated/kept by redundant reload.
The command line is:
arm-none-eabi-gcc -mthumb -mcpu=cortex-m0 -Os ...
