[PATCH] Fix encoding description for ARM post-indexed ldr instructions

[Mihail Popa]

Guys, may I commit this?

The absence of this additional constraint triggers an unfortunate behaviour
in the disassembler. For example:

echo "0xb0 0x00 0x10 0xe6" | llvm-mc -disassemble -show-inst -triple=armv7
-show-encoding

ldr r0, [r0], -r0, lsr #1   @ encoding: [0xa0,0x00,0x10,0xe6]
                                        @ <MCInst #205 LDR_POST_REG
                                        @  <MCOperand Reg:60>
                                        @  <MCOperand Reg:60>
                                        @  <MCOperand Reg:60>
                                        @  <MCOperand Reg:60>
                                        @  <MCOperand Imm:159745>
                                        @  <MCOperand Imm:14>
                                        @  <MCOperand Reg:0>>

Note the input and output encodings differ! This is because the input
encoding is actually undefined but accepted as a LDR.
We don't want that in a disassembler. I can also produce about 15 million
additional similar failures due to this oversight alone!

Thanks,
Mihai



On Fri, Apr 26, 2013 at 5:59 PM, Owen Anderson <resistor at mac.com> wrote:

> It looks OK to me offhand, but I have no memory of why the test was
> XFAIL'd initially.
>
> --Owen
>
> On Apr 26, 2013, at 8:54 AM, Rafael Espíndola <rafael.espindola at gmail.com>
> wrote:
>
> > Owen, this patch looks good to me, but it has been disabled since the
> > switch to the new arm disassembler. Would you mind double checking
> > that it is the correct fix?
> >
> > On 26 April 2013 11:46, Mihail Popa <mihail.popa at arm.com> wrote:
> >> Hello.
> >>
> >> This tightens up the encoding description for ARM post-indexed ldr
> >> instructions. All instructions in this class have bit 4 cleared. It
> turns
> >> out that there is a test case for this, but it was marked XFAIL.
> >>
> >> Regards,
> >> Mihai
> >>
> >> _______________________________________________
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> >> llvm-commits at cs.uiuc.edu
> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> >>
>
>
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