Bug#988965: llvm-toolchain-12: llvm 12 generates bad human-readable IR output on mipsel

[Ximin Luo]

Source: llvm-toolchain-12
Version: 1:12.0.0-3
Severity: important
X-Debbugs-Cc: debian-mips at lists.debian.org, debian-rust at lists.debian.org

Dear Maintainer,

LLVM 12's ability to emit IR in human-readable form is corrupted on mipsel 32-bit:

$ cat main.c 
#include <string.h>

int main() {
  char *a = NULL;
  char *b = NULL;
  memcpy(a, b, 0);
}
$ clang-12 -S -emit-llvm main.c
$ grep 00G8 main.ll
  call void @llvm.memcpy.00G8.00G8.G32(i8* align 1 %3, i8* align 1 %4, i32 0, i1 false)
declare void @llvm.memcpy.00G8.00G8.G32(i8* noalias nocapture writeonly, i8* noalias nocapture readonly, i32, i1 immarg) #1

00G8 is not correct, it should be p0i8 and suggests miscompilation somewhere as
the source code of the function does not contain these characters:

https://github.com/llvm/llvm-project/blob/5b6cae5524905bc43cfc21a515f828528d1f2e68/llvm/lib/IR/Function.cpp#L777

This additionally makes some rustc tests fail.

LLVM 11 is fine.

I filed a Debian bug for now because I could not find any other LLVM 12 mipsel
binaries to test with online; neither upstream nor Fedora distribute these.
Please do forward upstream if you are confident this is not a Debian-specific
issue.

X

-- System Information:
Debian Release: 11.0
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable-debug'), (500, 'testing-security'), (500, 'testing-debug'), (500, 'stable'), (300, 'unstable'), (100, 'experimental'), (1, 'experimental-debug')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.9.0-4-amd64 (SMP w/4 CPU threads)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled