[LLVMbugs] [Bug 11778] New: incorrectly narrowing switch cases before checking for duplicates

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=11778

             Bug #: 11778
           Summary: incorrectly narrowing switch cases before checking for
                    duplicates
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: richard-llvm at metafoo.co.uk
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified


<stdin>:1:34: warning: overflow converting case value to switch condition type
      (256 to 0) [-Wswitch]
int f(char c) { switch(c) { case 256: case 0: return 1; } return 0; }
                                 ^
<stdin>:1:44: error: duplicate case value '0'
int f(char c) { switch(c) { case 256: case 0: return 1; } return 0; }
                                           ^
<stdin>:1:34: note: previous case defined here
int f(char c) { switch(c) { case 256: case 0: return 1; } return 0; }
                                 ^

This is incorrect: the promoted type of the switch condition is 'int', and
there are no duplicate case values in this switch statement. The warning is
also incorrect, but it seems wise to produce some kind of warning for this
case: 'condition value can never equal case value' or similar.

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