Stream: git-wasmtime

Topic: wasmtime / issue #14168 Unnecessary stack checks and prol...

Wasmtime GitHub notifications bot (Aug 19 2026 at 20:04):

alexcrichton opened issue #14168:

Given this input:

(module
  (type $t (func))
  (global (export "g") (mut (ref $t)) (ref.func $f))
  (func $f)

  (func (export "call")
    (return_call_ref $t (global.get 0))
  )
)

this currently compiles as:

$ wasmtime compile foo.wat
$ wasmtime objdump foo.cwasm --filter 1
wasm[0]::function[1]:
            pushq   %rbp
            movq    %rsp, %rbp
            movq    8(%rdi), %r10
            movq    0x18(%r10), %r10
            addq    $0x10, %r10
            cmpq    %rsp, %r10
            ja      0x52
            movq    0x30(%rdi), %rsi
            movq    %rdi, %r8
            movq    8(%rsi), %r10
            ╰─╼ trap: Normal(NullReference)
            movq    0x18(%rsi), %rdi
            movq    %r8, %rsi
            movq    %rbp, %rsp
            popq    %rbp
            jmpq    *%r10
            ud2
            ╰─╼ trap: Normal(StackOverflow)

There's a few inefficiencies with this codegen we could improve upon:

• There's an explicit stack check as cmpq %rsp, %r10 here which isn't necessary. That's injected for functions in general which call another function, but it's not injected for leaf functions, and in this case this is sort of a leaf function.
• This sets up a prologue/epilogue which isn't necessary for this "mostly leaf" function.
• There's a trap registered for a null function reference, but this function reference type can't be null so that's not necessary.

Nothing major here, but might be nice to clean up some of this as well.

Wasmtime GitHub notifications bot (Aug 27 2026 at 16:56):

fitzgen added the cranelift:goal:optimize-speed label to Issue #14168.

Last updated: Aug 30 2026 at 09:07 UTC