https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89681
Bug ID: 89681
Summary: Incorrect source positions on O1 for simple code case
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: alahay01 at gcc dot gnu.org
Target Milestone: ---
Created attachment 45949
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45949&action=edit
source code
Compiling a simple test case with O1 gives incorrect line numbers for two of
the lines of assembly.
Tested this on HEAD, 6.4.0, 7.2.0, using both X86-64 and AArch64. Debug results
are the same for all.
$ gcc --version
gcc (Ubuntu 7.2.0-1ubuntu1~16.04) 7.2.0
$ cat -n consume.c
1 extern void consume(int);
2 void testfunc(int **p) {
3 int *a = *p;
4 int b = *a;
5 consume(b);
6 }
$ gcc -O1 -g consume.c -c -fdump-rtl-all
$ objdump -S -l -d consume.o
consume.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <testfunc>:
testfunc():
/home/alahay01/consume.c:2
extern void consume(int);
void testfunc(int **p) {
0: 48 83 ec 08 sub $0x8,%rsp
/home/alahay01/consume.c:4
int *a = *p;
int b = *a;
4: 48 8b 07 mov (%rdi),%rax
/home/alahay01/consume.c:5
consume(b);
7: 8b 38 mov (%rax),%edi
9: e8 00 00 00 00 callq e <testfunc+0xe>
/home/alahay01/consume.c:6
}
e: 48 83 c4 08 add $0x8,%rsp
12: c3 retq
>The two MOV instructions are on the wrong line. They are given lines 4 and 5.
>They should have lines 3 and 4.
$ cat consume.c.229r.expand
;; Function testfunc (testfunc, funcdef_no=0, decl_uid=1795, cgraph_uid=0,
symbol_order=0)
;; Generating RTL for gimple basic block 2
try_optimize_cfg iteration 1
Merging block 3 into block 2...
Merged blocks 2 and 3.
Merged 2 and 3 without moving.
Merging block 4 into block 2...
Merged blocks 2 and 4.
Merged 2 and 4 without moving.
try_optimize_cfg iteration 2
;;
;; Full RTL generated for this function:
;;
(note 1 0 4 NOTE_INSN_DELETED)
(note 4 1 2 2 [bb 2] NOTE_INSN_BASIC_BLOCK)
(insn 2 4 3 2 (set (reg/v/f:DI 89 [ p ])
(reg:DI 5 di [ p ])) "consume.c":2 -1
(nil))
(note 3 2 6 2 NOTE_INSN_FUNCTION_BEG)
(debug_insn 6 3 7 2 (var_location:DI a (mem/f:DI (reg/v/f:DI 89 [ p ]) [1
*p_2(D)+0 S8 A64])) "consume.c":3 -1
(nil))
(debug_insn 7 6 8 2 (var_location:SI b (mem:SI (mem/f:DI (reg/v/f:DI 89 [ p ])
[1 *p_2(D)+0 S8 A64]) [2 *a_3+0 S4 A32])) "consume.c":4 -1
(nil))
(insn 8 7 9 2 (set (reg/f:DI 90)
(mem/f:DI (reg/v/f:DI 89 [ p ]) [1 *p_2(D)+0 S8 A64])) "consume.c":4 -1
(nil))
(insn 9 8 10 2 (set (reg:SI 5 di)
(mem:SI (reg/f:DI 90) [2 *a_3+0 S4 A32])) "consume.c":5 -1
(nil))
(call_insn 10 9 0 2 (call (mem:QI (symbol_ref:DI ("consume") [flags 0x41]
<function_decl 0x7faaba359e00 consume>) [0 consume S1 A8])
(const_int 0 [0])) "consume.c":5 -1
(nil)
(expr_list:SI (use (reg:SI 5 di))
(nil)))
>Looks to me like it goes wrong in the expand phase. There are two debug_insn's
>for lines 3 and 4. But, then there are two insn's for line 4 and 5. I think
>these are incorrect, and should be lines 3 and 4.
>With O0 the results are correct:
$ gcc -O0 -g consume.c -c -fdump-rtl-all
$ objdump -S -l -d consume.o
consume.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <testfunc>:
testfunc():
/home/alahay01/consume.c:2
extern void consume(int);
void testfunc(int **p) {
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 83 ec 20 sub $0x20,%rsp
8: 48 89 7d e8 mov %rdi,-0x18(%rbp)
/home/alahay01/consume.c:3
int *a = *p;
c: 48 8b 45 e8 mov -0x18(%rbp),%rax
10: 48 8b 00 mov (%rax),%rax
13: 48 89 45 f8 mov %rax,-0x8(%rbp)
/home/alahay01/consume.c:4
int b = *a;
17: 48 8b 45 f8 mov -0x8(%rbp),%rax
1b: 8b 00 mov (%rax),%eax
1d: 89 45 f4 mov %eax,-0xc(%rbp)
/home/alahay01/consume.c:5
consume(b);
20: 8b 45 f4 mov -0xc(%rbp),%eax
23: 89 c7 mov %eax,%edi
25: e8 00 00 00 00 callq 2a <testfunc+0x2a>
/home/alahay01/consume.c:6
}
2a: 90 nop
2b: c9 leaveq
2c: c3 retq
$ cat consume.c.229r.expand
;; Function testfunc (testfunc, funcdef_no=0, decl_uid=1795, cgraph_uid=0,
symbol_order=0)
Partition 0: size 8 align 8
a_3
Partition 1: size 4 align 4
b_4
;; Generating RTL for gimple basic block 2
try_optimize_cfg iteration 1
Merging block 3 into block 2...
Merged blocks 2 and 3.
Merged 2 and 3 without moving.
Merging block 4 into block 2...
Merged blocks 2 and 4.
Merged 2 and 4 without moving.
try_optimize_cfg iteration 2
;;
;; Full RTL generated for this function:
;;
(note 1 0 4 NOTE_INSN_DELETED)
(note 4 1 2 2 [bb 2] NOTE_INSN_BASIC_BLOCK)
(insn 2 4 3 2 (set (mem/f/c:DI (plus:DI (reg/f:DI 82 virtual-stack-vars)
(const_int -24 [0xffffffffffffffe8])) [3 p+0 S8 A64])
(reg:DI 5 di [ p ])) "consume.c":2 -1
(nil))
(note 3 2 6 2 NOTE_INSN_FUNCTION_BEG)
(insn 6 3 7 2 (set (reg/f:DI 87)
(mem/f/c:DI (plus:DI (reg/f:DI 82 virtual-stack-vars)
(const_int -24 [0xffffffffffffffe8])) [3 p+0 S8 A64]))
"consume.c":3 -1
(nil))
(insn 7 6 8 2 (set (reg/f:DI 88)
(mem/f:DI (reg/f:DI 87) [1 *p_2(D)+0 S8 A64])) "consume.c":3 -1
(nil))
(insn 8 7 9 2 (set (mem/f/c:DI (plus:DI (reg/f:DI 82 virtual-stack-vars)
(const_int -8 [0xfffffffffffffff8])) [1 a+0 S8 A64])
(reg/f:DI 88)) "consume.c":3 -1
(nil))
(insn 9 8 10 2 (set (reg/f:DI 89)
(mem/f/c:DI (plus:DI (reg/f:DI 82 virtual-stack-vars)
(const_int -8 [0xfffffffffffffff8])) [1 a+0 S8 A64]))
"consume.c":4 -1
(nil))
(insn 10 9 11 2 (set (reg:SI 90)
(mem:SI (reg/f:DI 89) [2 *a_3+0 S4 A32])) "consume.c":4 -1
(nil))
(insn 11 10 12 2 (set (mem/c:SI (plus:DI (reg/f:DI 82 virtual-stack-vars)
(const_int -12 [0xfffffffffffffff4])) [2 b+0 S4 A32])
(reg:SI 90)) "consume.c":4 -1
(nil))
(insn 12 11 13 2 (set (reg:SI 91)
(mem/c:SI (plus:DI (reg/f:DI 82 virtual-stack-vars)
(const_int -12 [0xfffffffffffffff4])) [2 b+0 S4 A32]))
"consume.c":5 -1
(nil))
(insn 13 12 14 2 (set (reg:SI 5 di)
(reg:SI 91)) "consume.c":5 -1
(nil))
(call_insn 14 13 17 2 (call (mem:QI (symbol_ref:DI ("consume") [flags 0x41]
<function_decl 0x7f517cca5e00 consume>) [0 consume S1 A8])
(const_int 0 [0])) "consume.c":5 -1
(nil)
(expr_list:SI (use (reg:SI 5 di))
(nil)))
(insn 17 14 0 2 (const_int 0 [0]) "consume.c":6 -1
(nil))
