[llvm-bugs] [Bug 42138] New: Different codegen with/without -g

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42138

            Bug ID: 42138
           Summary: Different codegen with/without -g
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: DebugInfo
          Assignee: unassignedbugs at nondot.org
          Reporter: chris.dawson at sony.com
                CC: jdevlieghere at apple.com, keith.walker at arm.com,
                    llvm-bugs at lists.llvm.org,
                    paul_robinson at playstation.sony.com

Using the check-cfc tool (
https://github.com/llvm/llvm-project/tree/master/clang/utils/check_cfc ) to
spot a codegen difference depending on whether -g is specified or not.

$ cat PowerParser.ii.cc

template <typename, typename = int> class e;
class allocator {
public:
  ~allocator();
};
template <typename, typename> class e {
public:
  e(char *, allocator = allocator());
};
template <typename b, typename c, typename d> bool operator==(e<c, d>, b);
class f {
public:
  f(int *, int *, int *, int, int, int, int);
  e<char> g();
  void j();
};
int h, i;
class k {
  void l();
  bool m_fn4();
  int m;
  int n;
  int q;
  int fmap;
};
void k::l() {
  e<char> o = "";
  for (;;) {
    int p = 0;
    for (;;) {
      if (m_fn4())
        break;
      f a(&q, &fmap, &m, n, h, i, 0);
      if (a.g() == "")
        a.j();
    }
  }
}

$ ./llvm-project/clang/utils/check_cfc/clang++ PowerParser.ii.cc -w -c -O1 -o
tmp.ll

Check CFC, checking: dash_g_no_change
PowerParser.ii.cc Code difference detected with -g
--- /tmp/tmpcdg_LH.o

+++ /tmp/tmpfkaPkW.o

@@ -19,6 +19,6 @@

   28:  4c 8d 73 08             lea    0x8(%rbx),%r14
   2c:  4c 8d 7b 0c             lea    0xc(%rbx),%r15
   30:  4c 8d 64 24 08          lea    0x8(%rsp),%r12
-  35:  66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
-  3c:  00 00 00
-  3f:  90                      nop
+  35:  eb 09                   jmp    40 <_ZN1k1lEv+0x40>
+  37:  66 0f 1f 84 00 00 00    nopw   0x0(%rax,%rax,1)
+  3e:  00 00
*** Diff truncated ***

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