[llvm-dev] Understanding targets

Wed Nov 13 07:28:26 PST 2019

The term "target" is somewhat overloaded.
When llvm-config tells you it was built with the X86 target, that actually includes a variety of closely related architectures, such as x86_64, i386, and so on.  Within the x86_64 architecture, there are many individual processor implementations that LLVM understands, such as Skylake, Bulldozer, and many many more.
What *clang* means by "target" is really the target triple, which includes the architecture, OS, and sometimes other information.  For clang-cl the default triple is likely something along the lines of "x86_64-pc-msvc" and tends to be derived from the characteristics of the environment where you are running clang.
Clang accepts a -target option which allows you to specify a different triple.  The first component of the triple would have to be an architecture name that is supported by one of the LLVM targets that clang was built with.  So, to support triples starting with "x86_64" you would need a clang that includes the X86 target, and so on.

Regarding the Mips target, it looks like the supported 32-bit architecture names are "mips" and "mipsel" so you could experiment with using triples starting with those strings.  I don't know anything in particular about the Mips target other than what I just said.  I have cc'd the code owner of the MIPS target, who might be able to help you there.
--paulr

From: cfe-dev <cfe-dev-bounces at lists.llvm.org> On Behalf Of Gaier, Bjoern via cfe-dev
Sent: Wednesday, November 13, 2019 7:56 AM
To: Clang Dev <cfe-dev at lists.llvm.org>
Subject: [cfe-dev] Understanding targets

Heyho everyone,

I have a big noob question again! I basically want to know, how I can find out which processors a certain installation of Clang supports and how do I change the target processor.
Some background to make my question more clear:

Normally I develop applications for Windows and 64bit - back then using the MSVC compiler. By now I changed to the fantastic Clang-Cl and didn't thought much about processors - I take it automatically target x86-64 because of Visual Studio?

However, I know that Clang supports more processors (or architectures? What is the difference?) then x86-64. So I wanted to know, which are supported and how do I tell Clang do use a different target?

To give even more background:
I used an old development environment, which provided compiler for the old Playstation CPU - Wikipedia says it is a "32-bit RISC MIPS R3000A-compatible MIPS R3051" (I simply thought it is a R3000). And I started to wonder, how do I know if Clang supports that old CPU?

So I ran my llvm-config with --targets-built and got:
AArch64 AMDGPU ARM BPF Hexagon Lanai Mips MSP430 NVPTX PowerPC RISCV Sparc SystemZ WebAssembly X86 XCore

I see there "Mips" and "RISCV" but no RISC MIPS or even a R3000 - does that now mean that Clang does not support does old processors? Or does it? What do I do if I encounter a 'wild' Clang without llvm-config - can I still find out its targets? I have no idea and this is why I'm asking.

Thank you in advance for any help!

Kind greetings
Björn Gaier

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