[LLVMbugs] [Bug 1388] ARM THUMB: cpy instruction mustn't be emitted by default

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=1388

John Brawn <john.brawn.123 at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |john.brawn.123 at gmail.com
         Resolution|---                         |FIXED

--- Comment #7 from John Brawn <john.brawn.123 at gmail.com> ---
This was fixed by r216138:

Author: Jonathan Roelofs <jonathan at codesourcery.com>
Date:   Wed Aug 20 23:38:50 2014 +0000

    Lower thumbv4t & thumbv5 lo->lo copies through a push-pop sequence

    On pre-v6 hardware, 'MOV lo, lo' gives undefined results, so such copies
need to
    be avoided. This patch trades simplicity for implementation time at the
expense
    of performance... As they say: correctness first, then performance.

    See http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-August/075998.html for
a few
    ideas on how to make this better.

AsmParser also doesn't permit MOV lo, lo (or CPY, as it used to be known), so
you can't use it in embedded asm, but MC does permit it, so using clang to
assemble a .s file with --target=thumbv4t-none-eabi gives no error but should.
That's less of a problem though.

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