[llvm-bugs] [Bug 31170] New: [AARCH64] SIMD instructions are emitted without proper address alignment

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https://llvm.org/bugs/show_bug.cgi?id=31170

            Bug ID: 31170
           Summary: [AARCH64] SIMD instructions are emitted without proper
                    address alignment
           Product: clang
           Version: 3.8
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: sergio.moreira at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 17656
  --> https://llvm.org/bugs/attachment.cgi?id=17656&action=edit
Sample C code

Hi,

I'm compiling a very simple memset() implementation for AARCH64. See the
attached file.

clang is generating a couple of SIMD store instructions without checking if the
address is aligned. When run on a target (e.g. Hikey board) it crashes with an
alignment fault.

I tested both clang-3.8 that is available on Ubuntu 16.04 Server, as well as a
build of clang-4.0 from SVN.

$ /opt/llvm/bin/clang-4.0 --target=aarch64 -c -O2 LibC.c -o LibC.o -isystem
/usr/aarch64-linux-gnu/include/
$ aarch64-linux-gnu-objdump -d -x LibC.o
<snipped>
0000000000000088 <memset>:
  88:   b40002c2        cbz     x2, e0 <memset+0x58>
  8c:   f100805f        cmp     x2, #0x20
  90:   540001e3        b.cc    cc <memset+0x44>
  94:   927be84a        and     x10, x2, #0xffffffffffffffe0
  98:   b40001aa        cbz     x10, cc <memset+0x44>
  9c:   8b0a0008        add     x8, x0, x10
  a0:   cb0a0049        sub     x9, x2, x10
  a4:   4e010c20        dup     v0.16b, w1
  a8:   9100400b        add     x11, x0, #0x10
  ac:   aa0a03ec        mov     x12, x10
  b0:   ad3f8160        stp     q0, q0, [x11,#-16]    <- x11 can be unaligned.
<snipped>

Let me know if you need more information.

$ /opt/llvm/bin/clang-4.0 -v
clang version 4.0.0 (trunk 287757)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/llvm/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.4.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.0.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.4.0
Candidate multilib: .;@m64
Selected multilib: .;@m64

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