[Bug debug/98656] New: switchlower_O0 drops line number of switch

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98656

            Bug ID: 98656
           Summary: switchlower_O0 drops line number of switch
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

[ Originally filed as gdb PR at
https://sourceware.org/bugzilla/show_bug.cgi?id=27179 ]

Consider test-case small.c.
...
$ cat -n small.c
     1  #include <stdio.h>
     2
     3  void foo (int x, int y)
     4  {
     5    switch (x) {
     6      case 0: break;
     7      case 1: break;
     8      case 2: break;
     9      case 3:
    10        for (int z = 0; z < ({ if (y) break; 5; }); z++)
    11            break;
    12      case 4: break;
    13          default: break;
    14    }
    15  }
    16
    17  int main ()
    18  {
    19    foo (1, 1);  // L1
    20    foo (2, 1);  // L2
    21    printf("hello world!");  // L3
    22    return 0;
    23  }
...

With gcc-8, we have a .loc with line number 5 representing the switch
statement:
...
$ gcc-8 -O0 -g small.c -save-temps
$ cat small.s
foo:
.LFB0:
        .file 1 "small.c"
        .loc 1 4 1
        .cfi_startproc
        pushq   %rbp
        .cfi_def_cfa_offset 16
        .cfi_offset 6, -16
        movq    %rsp, %rbp
        .cfi_def_cfa_register 6
        movl    %edi, -20(%rbp)
        movl    %esi, -24(%rbp)
        .loc 1 5 3
        cmpl    $4, -20(%rbp)
        ja      .L13
...

With gcc-9 that .loc disappeared:
...
foo:
.LFB0:
        .file 1 "small.c"
        .loc 1 4 1
        .cfi_startproc
        pushq   %rbp
        .cfi_def_cfa_offset 16
        .cfi_offset 6, -16
        movq    %rsp, %rbp
        .cfi_def_cfa_register 6
        movl    %edi, -20(%rbp)
        movl    %esi, -24(%rbp)
        cmpl    $4, -20(%rbp)
        ja      .L13
...
and that's still the case with gcc-11.

Culprit is switchlower_O0.

With this compilation:
...
$ rm -f *.c.*; gcc-11 -O0 -g small.c -fdump-tree-all-lineno -save-temps
...
we have at a-small.c.234t.cplxlower0:
...
  <bb 2> :
  [small.c:5:3] switch (x_1(D)) <[small.c:13:2] default: <L10> [INV],
[small.c:6:5] case 0: <L0> [INV], [small.c:7:5] case 1: <L1> [INV],
[small.c:8:5] case 2: <L2> [INV], [small.c:9:5] case 3: <L3> [INV],
[small.c:12:5] case 4: <L8> [INV]>
...
and at a-small.c.236t.switchlower_O0:
...
  <bb 2> :
  switch (x_1(D)) <[small.c:13:2] default: <L10> [0.00%], [small.c:6:5] case 0:
<L0> [20.00%], [small.c:7:5] case 1: <L1> [20.00%], [small.c:8:5] case 2: <L2>
[20.00%], [small.c:9:5] case 3: <L3> [20.00%], [small.c:12:5] case 4: <L8>
[20.00%]>
...

Note the dropped "[small.c:5:3]" in front of "switch".