Re: -Wtautological-bitwise-compare error in arm-tdep.c

Luis Machado
2020-05-15T20:41:06Z

On 5/15/20 5:32 PM, Simon Marchi via Gdb-patches wrote:
> We get this error in arm-tdep.c when building with clang 11:
>
> CXX arm-tdep.o
> /home/smarchi/src/binutils-gdb/gdb/arm-tdep.c:934:29: error: bitwise comparison always evaluates to false [-Werror,-Wtautological-bitwise-compare]
> else if ((insn & 0xffb0) == 0xe950 /* ldrd Rt, Rt2,
> ~~~~~~~~~~~~~~~~^~~~~~~~~
>
> Indeed, this can never evaluate to true. I tried to look at what the condition
> should be, but it's a bit too deep into ARM instruction encoding for me. I am
> pretty sure that the corresponding section in the ARM Architecture Reference
> Manual [1] is F3.1.15, if somebody wants to take a stab at it.
>
> Simon
>
> [1] https://static.docs.arm.com/ddi0487/fb/DDI0487F_b_armv8_arm.pdf
>

Thanks for reporting this. I'll look into it. It may be a typo of some kind.