[Bug c++/103329] New: [11/12 Regression] Code divergence in debug info with -fdump-tree-original since r11-291-g0f50f6daa140186a

[marxin at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103329

            Bug ID: 103329
           Summary: [11/12 Regression] Code divergence in debug info with
                    -fdump-tree-original since r11-291-g0f50f6daa140186a
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: jason at gcc dot gnu.org
  Target Milestone: ---

Since the revision, the following test-case:

$ cat vectors.ii
template <typename>
struct __is_integer {
  enum { __value };
};
template <typename _Tp, bool = __is_integer<_Tp>::__value>
struct __promote {
  typedef double __type;
};
template <typename, typename _Up>
using __promote_2 = __promote<_Up>;
template <typename _Tp, typename _Up>
typename __promote_2<_Tp, _Up>::__type pow(_Tp, _Up) {}
template <typename>
struct Vector {
  typedef int iterator;
  virtual ~Vector();
};
template <int>
class DoFHandler;
template <int>
struct MappingQ1 {
  MappingQ1();
  static const unsigned vertex_mapping[];
};
template <>
const unsigned MappingQ1<3>::vertex_mapping[];
struct DerivativeApproximation {
  template <int dim, class InputVector>
  void approximate_second_derivative(const DoFHandler<dim> &,
                                     const InputVector &, Vector<float> &,
                                     unsigned);
  template <int>
  struct SecondDerivative {
    typedef int Derivative;
    double derivative_norm(const Derivative &);
  };
};
template <>
double DerivativeApproximation::SecondDerivative<3>::derivative_norm(
    const Derivative &) {
  int s(pow(s, 3));
}
template <int dim, class InputVector>
void DerivativeApproximation::approximate_second_derivative(
    const DoFHandler<dim> &, const InputVector &, Vector<float> &, unsigned) {
  static MappingQ1<dim> index_interval;
  Vector<float>::iterator derivative_norm_on_this_cell;
}
template void DerivativeApproximation::approximate_second_derivative(
    const DoFHandler<3> &, const double &, Vector<float> &, unsigned);

$ g++ -O1 -g -w -fPIC -shared vectors.ii -o 1 -fdump-tree-original=/dev/null &&
cp 1 2 && g++ -O1 -g -w -fPIC -shared vectors.ii -o 1 && diff 1 2
Binary files 1 and 2 differ

It makes difference in debug info:

$ objdump -W 1 > 11
$ objdump -W 2 > 22

$ diff -u 11 22
...
 Contents of the .eh_frame section:

@@ -86,7 +86,7 @@
     0000000000000000 0000000000000000 
   Length:                   60
   Version:                  2
-  Offset into .debug_info:  0x395
+  Offset into .debug_info:  0x3b2
   Pointer Size:             8
   Segment Size:             0

@@ -111,21 +111,21 @@
     <1d>   DW_AT_producer    : (indirect string, offset: 0x32): GNU AS 2.37
     <21>   DW_AT_language    : 32769   (MIPS assembler)
   Compilation Unit @ offset 0x23:
-   Length:        0x36e (32-bit)
+   Length:        0x38b (32-bit)
    Version:       5
    Unit Type:     DW_UT_compile (1)
    Abbrev Offset: 0x12
    Pointer Size:  8
  <0><2f>: Abbrev Number: 17 (DW_TAG_compile_unit)
-    <30>   DW_AT_producer    : (indirect string, offset: 0x2ab): GNU C++17
12.0.0 20211118 (experimental) -mtune=generic -march=x86-64 -g -O1 -fPIC
+    <30>   DW_AT_producer    : (indirect string, offset: 0x2c5): GNU C++17
12.0.0 20211118 (experimental) -mtune=generic -march=x86-64 -g -O1 -fPIC
     <34>   DW_AT_language    : 33      (C++14)
     <35>   DW_AT_name        : (indirect line string, offset: 0x19):
vectors.ii
     <39>   DW_AT_comp_dir    : (indirect line string, offset: 0x24):
/home/marxin/Programming/testcases
     <3d>   DW_AT_ranges      : 0x2d
     <41>   DW_AT_low_pc      : 0x0
     <49>   DW_AT_stmt_list   : 0x67
...