cmd/compile: internal compiler error: panic during prove

[ALTree]

$ gotip version
go version devel go1.24-760b722c Fri Aug 9 14:54:31 2024 +0000 linux/amd64

package p

var v []func()

func f(i int) {
	v = make([]func(), -2|i)
}

$ gotip build crash.go
# command-line-arguments
./crash.go:7:1: internal compiler error: 'f': panic during prove while compiling f:

runtime error: invalid memory address or nil pointer dereference

goroutine 9 [running]:
cmd/compile/internal/ssa.Compile.func1()
	./desktop/gotip/src/cmd/compile/internal/ssa/compile.go:49 +0x6c
panic({0xdacd40?, 0x14e8b40?})
	./desktop/gotip/src/runtime/panic.go:785 +0x132
cmd/compile/internal/ssa.removeBranch(0x0, 0x0)
	./desktop/gotip/src/cmd/compile/internal/ssa/prove.go:2160 +0x22

...

[ALTree]

cc @randall77

[gabyhelp]

Related Issues and Documentation

• cmd/compile: internal compiler error: panic during lower (part 2) #30257 (closed)
• cmd/compile: panic: internal error: can't locate after prolog value (with -N -l) #45948 (closed)
• cmd/compile: internal compiler error: panic during expand calls [on ARM and other 32bit archs] #63462 (closed)
• cmd/compile: internal compiler error: panic during layout #23504 (closed)
• cmd/compile: internal compiler error: panic: runtime error when clearing empty struct slice #61127 (closed)
• cmd/compile: internal compiler error: panic: builtins.go: assertion failed #61486 (closed)
• cmd/compile: internal compiler error: panic during prove #26043 (closed)
• cmd/compile: internal compiler error: panic during short circuit #45947 (closed)
• cmd/compile: panic: runtime error: invalid memory address or nil pointer dereference [dev.regabi] #43701 (closed)
• cmd/compile: internal compiler error: aliasing constant which is not registered #35157 (closed)

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[randall77]

The reason it is panicking is because prove thinks the first block of the function is unreachable. I think there is some confusion lurking here between "unreachable" and "unconditionally panics" (the first block of f is the latter, but it isn't the former).

This is maybe a better example:

package p

var v []func()

func f(i, j int) {
	if j > 0 {
		v = make([]func(), -2|i)
	}
}

This function currently compiles to just RET. It should compile to something that will panic if j>0.

[gopherbot]

Change https://go.dev/cl/604118 mentions this issue: cmd/compile: in prove pass, check for unsat before adding local facts