I run into a strange error with Clang-Cl - I hope I can explain it. We use Clang-Cl via the LLVM extension in Visual Studio and use it to compile our source code. One of the flags we set for the compiler is “/FA” which gives us assembly output. Everything fine so far, no problems.
I then add a simple copy loop to our code, that is copying int32 values from one address to another one. When compiling this construct Clang-Cl suddenly exited with: “error: invalid instruction mnemonic ‘movsdi’”.
However, when I remove the “/FA” flag everything compiles fine and runs fine in the end… Strangely, I couldn’t figure out what the “movsdi” mnemonic is…
The Assembly code looks like this:
.LBB15_31: # in Loop: Header=BB15_17 Depth=1
mov ecx, 32
mov edx, 4
mov qword ptr [r12 + rbp + 96], rax
mov qword ptr [r12 + rbp + 88], rax
mov ecx, 32
mov rdi, rax
rep movsdi es:[rdi], [rsi]
My Clang-Cl version is:
clang version 11.0.0 (https://github.com/llvm/llvm-project.git 176249bd6732a8044d457092ed932768724a6f06)
Thread model: posix
The target is the same as in the version (x86_64-pc-windows-msvc).
Does anyone know what is going on?