[llvm-bugs] [Bug 47232] New: Missing debug line information for some cases

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47232

            Bug ID: 47232
           Summary: Missing debug line information for some cases
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: i at i-m.dev
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

Look at this simple code, we compile it with `clang -O0 -g main.c`

int main() {
    int v = -42;
    do {
        if (v <= 0) {
            v = 1024 - v;
        } else if (v % 2) {
            v = v * 3 + 1;
        } else {
            v = v / 2;
        } // here the debug becomes 0
    } while (1 != v);
}


However, clang generate wrong debug line information for the `}` line of second
else statement. line of address `0x000000000040116d` is zero. I tried on
Linux/macOS for various versions of clang, the problem reproduced.


Address            Line   Column File   ISA Discriminator Flags
------------------ ------ ------ ------ --- ------------- -------------
0x0000000000401110      1      0      1   0             0  is_stmt
0x000000000040111b      2      9      1   0             0  is_stmt prologue_end
0x0000000000401122      4     15      1   0             0  is_stmt
0x0000000000401126      4     13      1   0             0 
0x000000000040112c      5     22      1   0             0  is_stmt
0x0000000000401134      5     15      1   0             0 
0x0000000000401137      6      9      1   0             0  is_stmt
0x000000000040113c      6     20      1   0             0 
0x000000000040113f      6     22      1   0             0 
0x000000000040114a      6     20      1   0             0 
0x0000000000401150      7     19      1   0             0  is_stmt
0x0000000000401154      7     23      1   0             0 
0x0000000000401157      7     15      1   0             0 
0x000000000040115a      8      9      1   0             0  is_stmt
0x000000000040115f      9     17      1   0             0  is_stmt
0x0000000000401162      9     19      1   0             0 
0x000000000040116a      9     15      1   0             0 
0x000000000040116d      0     15      1   0             0 
0x0000000000401172     11      5      1   0             0  is_stmt
0x0000000000401177     11     16      1   0             0 
0x000000000040117f     11      5      1   0             0 
0x0000000000401185     12      1      1   0             0  is_stmt
0x000000000040118a     12      1      1   0             0  is_stmt end_sequence



0000000000401110 <main>:
  401110:       55                      push   %rbp
  401111:       48 89 e5                mov    %rsp,%rbp
  401114:       c7 45 fc 00 00 00 00    movl   $0x0,-0x4(%rbp)
  40111b:       c7 45 f8 d6 ff ff ff    movl   $0xffffffd6,-0x8(%rbp)
  401122:       83 7d f8 00             cmpl   $0x0,-0x8(%rbp)
  401126:       0f 8f 10 00 00 00       jg     40113c <main+0x2c>
  40112c:       b8 00 04 00 00          mov    $0x400,%eax
  401131:       2b 45 f8                sub    -0x8(%rbp),%eax
  401134:       89 45 f8                mov    %eax,-0x8(%rbp)
  401137:       e9 36 00 00 00          jmpq   401172 <main+0x62>
  40113c:       8b 45 f8                mov    -0x8(%rbp),%eax
  40113f:       99                      cltd   
  401140:       b9 02 00 00 00          mov    $0x2,%ecx
  401145:       f7 f9                   idiv   %ecx
  401147:       83 fa 00                cmp    $0x0,%edx
  40114a:       0f 84 0f 00 00 00       je     40115f <main+0x4f>
  401150:       6b 45 f8 03             imul   $0x3,-0x8(%rbp),%eax
  401154:       83 c0 01                add    $0x1,%eax
  401157:       89 45 f8                mov    %eax,-0x8(%rbp)
  40115a:       e9 0e 00 00 00          jmpq   40116d <main+0x5d>
  40115f:       8b 45 f8                mov    -0x8(%rbp),%eax
  401162:       99                      cltd   
  401163:       b9 02 00 00 00          mov    $0x2,%ecx
  401168:       f7 f9                   idiv   %ecx
  40116a:       89 45 f8                mov    %eax,-0x8(%rbp)
  40116d:       e9 00 00 00 00          jmpq   401172 <main+0x62>
  401172:       e9 00 00 00 00          jmpq   401177 <main+0x67>
  401177:       b8 01 00 00 00          mov    $0x1,%eax
  40117c:       3b 45 f8                cmp    -0x8(%rbp),%eax
  40117f:       0f 85 9d ff ff ff       jne    401122 <main+0x12>
  401185:       8b 45 fc                mov    -0x4(%rbp),%eax
  401188:       5d                      pop    %rbp
  401189:       c3                      retq

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