[LLVMbugs] [Bug 3568] New: clang arbitrary-width integer types don't calculate size/ alignment correctly

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=3568

           Summary: clang arbitrary-width integer types don't calculate
                    size/alignment correctly
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Semantic Analyzer
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: sharparrow1 at yahoo.com
                CC: llvmbugs at cs.uiuc.edu


I added support for arbitrary-width integer types in r64434.  The one known bug
in the implementation is that Sema doesn't calculate the size/alignment
consistently with LLVM.  (And for 128-bit integers, it calculates the alignment
to be 128 bits, which as far as I know is not consistent with gcc's TImode.)

LLVM logic for determining the size/alignment:
If there is at least one known integer type whose bitwidth is equal to or
larger than the bitwidth of the given integer type, the alignment is that of
the smallest such type.  Otherwise, the alignment is the alignment of the
largest known integer type.  The size is then the bitwidth plus whatever
padding is necessary to satisfy the alignment.

What makes this non-trivial is that TargetInfo doesn't expose a list of integer
types outside of the target description string, and it's definitely too much
work to parse the target description.


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