[MC][Thumb2] .w suffix rejected for certain ldr and str operands

[Quuxplusone]

Bugzilla Link	PR50664
Status	NEW
Importance	P enhancement
Reported by	Ryan Prichard (rprichard@google.com)
Reported on	2021-06-10 17:09:28 -0700
Last modified on	2021-06-11 10:11:10 -0700
Version	trunk
Hardware	PC Linux
CC	kristof.beyls@arm.com, llvm-bugs@lists.llvm.org, ndesaulniers@google.com, smithp352@googlemail.com, Ties.Stuij@arm.com
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LLVM can assemble this Thumb2 code (clang --target=armv7a-linux-gnueabi):

    .syntax unified
    .thumb
    ldr.w r0, [r1, #0xf00]

But not this:

    .syntax unified
    .thumb
    ldr.w r0, [r1, #-2]

test.S:3:15: error: invalid operand for instruction
    ldr.w r0, [r1, #-2]
              ^

It will assemble if I remove the ".w" suffix. The disassembly is then:

00000000 <.text>:
   0:   f851 0c02   ldr.w   r0, [r1, #-2]

... which indicates a wide instruction.

Maybe the fix for bug #49118 was incomplete?

There are some similar instructions that, IIRC, use the same encoding, and have
the same problem. They're wide instructions that can only be assembled if the
".w" suffix is omitted:

    ldr.w r0, [r1, #2]!
    ldr.w r0, [r1], #2
    ldr.w r0, [r1, #-0]

[Quuxplusone]

> ldr.w r0, [r1, #2]!
> ldr.w r0, [r1], #2
> ldr.w r0, [r1, #-0]

Actually it looks like a current version of LLVM can handle the first two of
these. Only the last one is a problem, and that's basically the same as "ldr.w
r0, [r1, #-2]".