[LLVMbugs] [Bug 6502] New: Clang complains about indirect goto jumping over initializations where GCC doesn't

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=6502

           Summary: Clang complains about indirect goto jumping over
                    initializations where GCC doesn't
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P5
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: chandlerc at gmail.com
                CC: llvmbugs at cs.uiuc.edu, dgregor at apple.com


I know this code is terrifying, but some code generators produce this type of
pattern. The rationale for the combined switch and manually built indirect goto
table is to turn the goto-based solution off on compilers which don't support
it, and on for those that do. I haven't tried to reduce it by de-interleaving
them, not sure if that's relevant or not. It might be possible to reduce this
further, but this makes it an "interesting" test case without being enormous.

% cat t.cc                      
bool f(const unsigned* indices) {
  static void* const dispatch_table[] = {
    &&L1,
    &&LEND,
  };
  for (const unsigned* next = indices; ; ) {
    goto *dispatch_table[*next];
    switch (*(next)) {
L1:
      case 0: {
        const int foo = 1.0;
        (void)foo;
        goto *dispatch_table[*(++next)];
        break;
      }
LEND:
      case 1:
      return true;
    }
  }
}

% ./bin/clang -fsyntax-only t.cc
t.cc:13:9: error: illegal indirect goto in protected scope, unknown effect on
scopes
        goto *dispatch_table[*(++next)];
        ^
t.cc:11:19: note: jump bypasses variable initialization
        const int foo = 1.0;
                  ^
t.cc:6:24: note: jump bypasses variable initialization
  for (const unsigned* next = indices; ; ) {
                       ^
t.cc:7:5: error: illegal indirect goto in protected scope, unknown effect on
scopes
    goto *dispatch_table[*next];
    ^
t.cc:6:24: note: jump bypasses variable initialization
  for (const unsigned* next = indices; ; ) {
                       ^
t.cc:4:5: error: address taken of label in protected scope, jump to it would
have unknown effect on scope
    &&LEND,
    ^
t.cc:6:24: note: jump bypasses variable initialization
  for (const unsigned* next = indices; ; ) {
                       ^
t.cc:3:5: error: address taken of label in protected scope, jump to it would
have unknown effect on scope
    &&L1,
    ^
t.cc:6:24: note: jump bypasses variable initialization
  for (const unsigned* next = indices; ; ) {
                       ^
9 diagnostics generated.

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