[llvm-dev] Is this a bug or is llvm processing conservative?

[Hiroshi Yamauchi via llvm-dev]

Perhaps "(*b)[2]" is out of bounds?

On Mon, Apr 27, 2020 at 8:57 PM Panyuntao(Compiler) via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi, All developers:
>
>
>
> *I have this code. For (*b)[2], It is reasonable that llvm thinks it's
> unaligned access. and I think the array pointer always points to 4 - byte
> aligned array elements.*
>
>
>
> CMD: clang  --target=arm-none-eabi -mcpu=cortex-r52 -mthumb -O0 -emit-llvm
> -S test.c -o test.ll
>
> *LLVM think it’s an align 1 store, I don't think so.*
>
> CMD: llc -mattr=+strict-align test.ll
>
> *If the CPU does not support non-aligned access, The access is divided
> into four one-byte access.*
>
>
>
> CMD: llc -mattr=-strict-align test.ll
>
> *If the CPU support non-aligned access, It's a normal four-byte access.*
>
>
>
> *But gcc always think it’s an aligned access ,and processed him as a
> four-byte access. I think this is reasonable.*
>
> CMD1: arm-none-eabi-gcc -mcpu=cortex-r52 -mthumb  -munaligned-access -O0
> -emit-llvm -S test.c -o test.s
>
> CMD2: arm-none-eabi-gcc -mcpu=cortex-r52 -mthumb  -mno-unaligned-access
> -O0 -emit-llvm -S test.c -o test.s
>
>
>
> *Why does LLVM think it's a one-byte-aligned access? I think it makes more
> sense to access the number of aligned based on the type of the array
> element to which the array pointer points*
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