https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105772
Bug ID: 105772
Summary: [debug, i386] sched2 moves get_pc_thunk call past
debug_insn
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
Target Milestone: ---
Consider the test-case source gdb/testsuite/gdb.base/break1.c (
https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=gdb/testsuite/gdb.base/break1.c;h=24d0d15dc2e8bd14f6b14fabbb38fec43db9c990;hb=HEAD
) containing function marker4.
Extracting the relevant part:
...
struct some_struct
{
int a_field;
int b_field;
union { int z_field; };
};
struct some_struct values[50];
void marker4 (long d) { values[0].a_field = d; } /* set breakpoint 14
here */
...
When compiling with gcc 12.1.0 and -O2 like so:
...
$ gcc -fno-stack-protector -m32 -fPIE -pie -w -c -g break1.c -O2
...
we have before sched2:
...
(note 4 1 14 2 [bb 2] NOTE_INSN_BASIC_BLOCK)
(note 14 4 11 2 NOTE_INSN_PROLOGUE_END)
(insn/f 11 14 3 2 (parallel [
(set (reg:SI 0 ax [82])
(unspec:SI [
(const_int 0 [0])
] UNSPEC_SET_GOT))
(clobber (reg:CC 17 flags))
]) 931 {*set_got}
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_EQUIV (unspec:SI [
(const_int 0 [0])
] UNSPEC_SET_GOT)
(expr_list:REG_CFA_FLUSH_QUEUE (nil)
(nil)))))
(note 3 11 6 2 NOTE_INSN_FUNCTION_BEG)
(debug_insn 6 3 12 2 (debug_marker) "break1.c":59:25 -1
(nil))
(insn 12 6 8 2 (set (reg/v:SI 1 dx [orig:83 d ] [83])
(mem/c:SI (plus:SI (reg/f:SI 7 sp)
(const_int 4 [0x4])) [5 d+0 S4 A32])) "break1.c":59:43 81
{*movsi_internal}
(expr_list:REG_EQUIV (mem/c:SI (reg/f:SI 16 argp) [5 d+0 S4 A32])
(nil)))
...
and after:
...
(note 4 1 14 2 [bb 2] NOTE_INSN_BASIC_BLOCK)
(note 14 4 3 2 NOTE_INSN_PROLOGUE_END)
(note 3 14 6 2 NOTE_INSN_FUNCTION_BEG)
(debug_insn 6 3 11 2 (debug_marker) "break1.c":59:25 -1
(nil))
(insn/f:TI 11 6 12 2 (parallel [
(set (reg:SI 0 ax [82])
(unspec:SI [
(const_int 0 [0])
] UNSPEC_SET_GOT))
(clobber (reg:CC 17 flags))
]) 931 {*set_got}
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_EQUIV (unspec:SI [
(const_int 0 [0])
] UNSPEC_SET_GOT)
(expr_list:REG_CFA_FLUSH_QUEUE (nil)
(nil)))))
(insn 12 11 8 2 (set (reg/v:SI 1 dx [orig:83 d ] [83])
(mem/c:SI (plus:SI (reg/f:SI 7 sp)
(const_int 4 [0x4])) [5 d+0 S4 A32])) "break1.c":59:43 81
{*movsi_internal}
(expr_list:REG_EQUIV (mem/c:SI (reg/f:SI 16 argp) [5 d+0 S4 A32])
(nil)))
...
This moves the get_pc_thunk call after the debug_insn, making it (in terms of
debug info) part of the first statement instead of the prologue.
That is, with -O1 we have insn:
...
0000000d <marker4>:
d: e8 fc ff ff ff call e <marker4+0x1>
12: 05 01 00 00 00 add $0x1,%eax
17: 8b 54 24 04 mov 0x4(%esp),%edx
1b: 89 90 00 00 00 00 mov %edx,0x0(%eax)
21: c3 ret
...
and line info:
...
File name Line number Starting address View Stmt
break1.c 59 0xd x
break1.c 59 0xd 1
break1.c 59 0x17 x
break1.c 59 0x17 1
break1.c 59 0x21
break1.c - 0x22
...
so at 0x17 we have the start of a statement.
But with -O2 we have identical insn:
...
00000030 <marker4>:
30: e8 fc ff ff ff call 31 <marker4+0x1>
35: 05 01 00 00 00 add $0x1,%eax
3a: 8b 54 24 04 mov 0x4(%esp),%edx
3e: 89 90 00 00 00 00 mov %edx,0x0(%eax)
44: c3 ret
...
but different line info:
...
File name Line number Starting address View Stmt
break1.c 59 0x30 x
break1.c 59 0x30 1 x
break1.c 59 0x3a
break1.c 59 0x44
break1.c - 0x45
...
so at 0x3a we don't have the start of a statement.
