cmd/compile: unnecessary bounds check when slicing after using `slices.Grow`

[dominikh]

Go version

go version go1.24.1 linux/amd64

Output of go env in your module/workspace:

-

What did you do?

package pkg

import "slices"

func Foo() {
	var xs []int
	xs = slices.Grow(xs, 4)[:len(xs)+4]
}

What did you see happen?

Slicing after growing inserts a check for the capacity and a conditional call to runtime.panicSliceAcap

What did you expect to see?

The compiler should be able to tell that we just guaranteed that the slice's capacity is at least len(xs)+4 and shouldn't insert another check.

[gabyhelp]

Related Issues

• cmd/compile: don't generate call to growslice if the slice has capacity #33853 (closed)
• cmd/compile: unnecessary runtime.growslice with provable capacity #66692 (closed)
• runtime: significant number of bounds checks in growslice #60071
• cmd/compile: unnecessary bounds check for position len/2 #27249 (closed)
• slices: better panic message for out of range Insert #64152
• cmd/compile: impossible slice access is compiled in spite of always panicking #27250 (closed)
• cmd/compile: bce: if slice[n] is in bounds, then slice[:n+1] should have bounds check eliminated #32431 (closed)
• cmd/compile: No BCE for len(x)&y in slice expression #52563 (closed)
• cmd/compile: missed bounds check elimination when paired slices are resliced #70062
• cmd/compile: unnecessary bounds check #29872

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[Guvanchhojamov]

@dominikh Hey, Can you provide go env output please, on above description it is empty.
And how you can see here

https://github.com/golang/go/blob/3fd729b2a14a7efcf08465cbea60a74da5457f06/src/slices/slices.go#L410C45-L411C37

// If n is negative or too large to allocate the memory, Grow panics.
It can panic.