Cranelift, a low-level retargetable code generator written in Rust (opens in new tab)

(github.com)

63 pointsexrook7y ago32 comments

32 comments

28 comments · 7 top-level

smaddox7y ago· 8 in thread

It's interesting that booleans are stored as 0 or -1 [1]. I wonder what drove that decision. I just checked, and Rust's LLVM stores booleans as 0 or 1.

[1] https://cranelift.readthedocs.io/en/latest/ir.html#boolean-t...

KMag7y ago

Well, for one, if true is -1 (using two's complement), then a bunch of conditionals and bit-twiddling become more simple. For instance:

    x = some_bool ? a : b;

can be compiled as a branchless:

    x = (some_bool & a) | (~some_bool & b);

This is why Forth also represents true as -1.

pcwalton7y ago

Also why SIMD fairly universally uses -1 for true.

C arguably picked the wrong semantics here. Hardware picks up the slack, however, with the setcc instructions on x86, csinc on AArch64, etc.

eridius7y ago

That would only be true if `a` is guaranteed to be a non-zero value though, right? e.g. `x = some_bool ? 0 : 1` would not be able to be represented that way.

1 more reply

sunfish7y ago

A typical Rust bool would use `b1`, which doesn't have an observable representation.

steveklabnik7y ago

We did, eventually, after years, define it as a full byte though. https://github.com/rust-lang/rust/pull/46156

sunfish7y ago

Also, the [bint instruction](https://cranelift.readthedocs.io/en/latest/ir.html#inst-bint) converts a bool value to an integer 0 or 1.

cpeterso7y ago

Boolean true is -1 in Visual Basic, too: https://docs.microsoft.com/en-us/dotnet/visual-basic/languag...

perl4ever7y ago

It was traditional in earlier BASICs too; I think I remember it being the case in QuickBASIC and AmigaBASIC.

I assume someone once upon a time thought it was a nice thing for ~x to be equal to !x.

xvilka7y ago· 4 in thread

Hopefully will replace LLVM one day.

pjmlp7y ago

It will be an herculean effort though, given the amount of companies that contribute to LLVM.

sunfish7y ago

Fortunately, this isn't required for the project to be successful :-).

1 more reply

mamcx7y ago

Not as "replace" but be a decent alternative, easier and less complicated?

qznc7y ago

Faster would be the most desirable attribute in my opinion. Rust should be much faster at least for development builds and LLVM is one of the parts which slows it down.

ndh27y ago· 3 in thread

Any example or tutorial?

dmytrish7y ago

I can't say if it's complete or work in progress, but here is a demo: https://github.com/sunfishcode/simplejit-demo

smaddox7y ago

Nice! This should be amazing for writing toy compiled languages! This looks way easier to get up and running than an LLVM backend.

sunfish7y ago

There's a tutorial in development, but it's not finished yet. So right now isn't the optimal time for an HN post, but HN doesn't always ask people before linking to their projects ¯\_(ツ)_/¯.

jeandejean7y ago· 3 in thread

I understand the enthusiasm for Rust, but I'm growing tired of these project advertised as "written in Rust" like it proves a point in itself.

sunfish7y ago

Fwiw, "written in Rust" was added by whoever submitted the HN link; the project's own web page and documentation don't describe it like that.

stmw7y ago

Sure, it doesn't prove a point, but the headline does show the level of growth Rust is enjoying... It's not that different than "game X on Linux" in the early days, or "ML in Python".

Apaec7y ago

I grow tired of "written in Go" or "written in Python". At least Rust means high performance and no GC.

steveklabnik7y ago· 2 in thread

Previously called “cretone”, by the way.

cpeterso7y ago

I heard that the project was renamed because no one could pronounced "Cretonne". :)

stmw7y ago

Plus it has the danger of sounding too much like "cretin"

kodablah7y ago· 1 in thread

Does it, or are there plans to, translate the IR to WASM (i.e. a WASM backend instead of just frontend)? This seems to have a more expressive set of instructions than WASM and could be a good target for compilers.

sunfish7y ago

It is something we're thinking about. You might have to limit yourself to a subset of the full Cranelift IR for this, but I think we could make that subset big enough to be interesting.

seeekr7y ago

The README says:

"Cranelift is designed to be a code generator for WebAssembly, but it is general enough to be useful elsewhere too. The initial planned uses that affected its design are:

WebAssembly compiler for the SpiderMonkey engine in Firefox. Backend for the IonMonkey JavaScript JIT compiler in Firefox. Debug build backend for the Rust compiler."

j / k navigate · click thread line to collapse

32 comments

28 comments · 7 top-level

smaddox7y ago· 8 in thread

It's interesting that booleans are stored as 0 or -1 [1]. I wonder what drove that decision. I just checked, and Rust's LLVM stores booleans as 0 or 1.

[1] https://cranelift.readthedocs.io/en/latest/ir.html#boolean-t...

KMag7y ago

Well, for one, if true is -1 (using two's complement), then a bunch of conditionals and bit-twiddling become more simple. For instance:

    x = some_bool ? a : b;

can be compiled as a branchless:

    x = (some_bool & a) | (~some_bool & b);

This is why Forth also represents true as -1.

pcwalton7y ago

Also why SIMD fairly universally uses -1 for true.

C arguably picked the wrong semantics here. Hardware picks up the slack, however, with the setcc instructions on x86, csinc on AArch64, etc.

eridius7y ago

That would only be true if `a` is guaranteed to be a non-zero value though, right? e.g. `x = some_bool ? 0 : 1` would not be able to be represented that way.

1 more reply

sunfish7y ago

A typical Rust bool would use `b1`, which doesn't have an observable representation.

steveklabnik7y ago

We did, eventually, after years, define it as a full byte though. https://github.com/rust-lang/rust/pull/46156

sunfish7y ago

Also, the [bint instruction](https://cranelift.readthedocs.io/en/latest/ir.html#inst-bint) converts a bool value to an integer 0 or 1.

cpeterso7y ago

Boolean true is -1 in Visual Basic, too: https://docs.microsoft.com/en-us/dotnet/visual-basic/languag...

perl4ever7y ago

It was traditional in earlier BASICs too; I think I remember it being the case in QuickBASIC and AmigaBASIC.

I assume someone once upon a time thought it was a nice thing for ~x to be equal to !x.

xvilka7y ago· 4 in thread

Hopefully will replace LLVM one day.

pjmlp7y ago

It will be an herculean effort though, given the amount of companies that contribute to LLVM.

sunfish7y ago

Fortunately, this isn't required for the project to be successful :-).

1 more reply

mamcx7y ago

Not as "replace" but be a decent alternative, easier and less complicated?

qznc7y ago

Faster would be the most desirable attribute in my opinion. Rust should be much faster at least for development builds and LLVM is one of the parts which slows it down.

ndh27y ago· 3 in thread

Any example or tutorial?

dmytrish7y ago

I can't say if it's complete or work in progress, but here is a demo: https://github.com/sunfishcode/simplejit-demo

smaddox7y ago

Nice! This should be amazing for writing toy compiled languages! This looks way easier to get up and running than an LLVM backend.

sunfish7y ago

There's a tutorial in development, but it's not finished yet. So right now isn't the optimal time for an HN post, but HN doesn't always ask people before linking to their projects ¯\_(ツ)_/¯.

jeandejean7y ago· 3 in thread

I understand the enthusiasm for Rust, but I'm growing tired of these project advertised as "written in Rust" like it proves a point in itself.

sunfish7y ago

Fwiw, "written in Rust" was added by whoever submitted the HN link; the project's own web page and documentation don't describe it like that.

stmw7y ago

Sure, it doesn't prove a point, but the headline does show the level of growth Rust is enjoying... It's not that different than "game X on Linux" in the early days, or "ML in Python".

Apaec7y ago

I grow tired of "written in Go" or "written in Python". At least Rust means high performance and no GC.

steveklabnik7y ago· 2 in thread

Previously called “cretone”, by the way.

cpeterso7y ago

I heard that the project was renamed because no one could pronounced "Cretonne". :)

stmw7y ago

Plus it has the danger of sounding too much like "cretin"

kodablah7y ago· 1 in thread

sunfish7y ago

It is something we're thinking about. You might have to limit yourself to a subset of the full Cranelift IR for this, but I think we could make that subset big enough to be interesting.

seeekr7y ago

The README says:

"Cranelift is designed to be a code generator for WebAssembly, but it is general enough to be useful elsewhere too. The initial planned uses that affected its design are:

WebAssembly compiler for the SpiderMonkey engine in Firefox. Backend for the IonMonkey JavaScript JIT compiler in Firefox. Debug build backend for the Rust compiler."

j / k navigate · click thread line to collapse