[llvm-bugs] [Bug 45136] New: -Xclang -malign-double lowers alignment of long double to 8

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Mar 6 05:39:07 PST 2020


            Bug ID: 45136
           Summary: -Xclang -malign-double lowers alignment of long double
                    to 8
           Product: clang
           Version: 9.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: blaz.tomazic at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

Created attachment 23214
  --> https://bugs.llvm.org/attachment.cgi?id=23214&action=edit

When compiling with `-Xclang -malign-double` the `alignof(long double)` returns
8, while without the flags it returns 16. Basically the alignment is lowered.

I am not sure if this is the intended behaviour, I guess that this flag should
only set alignment on `double` from 4 to 8 on 32-bit systems.

For comparison GCC returns 16 with or without the flag `-malign-double`.

Tested on Linux x86-64 and OSX x86-64 (clang also with `-m32`). I suppose that
for 64-bit builds it should do nothing but it still lowered the alignment.

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