cmd/compile: nil check stack reported at write instead of previous nil check

[randall77]

package main

type T struct {
	a int
}

func (t *T) foo() {
	t.a = 3
}

func main() {
	var t *T
	(*t).foo()
}

This should panic at the second line of main, not inside foo.

Good stack trace:

main.main()
	/Users/khr/tmp6.go:13 +0x8

Bad stack trace:

main.(*T).foo(...)
	/Users/khr/tmp6.go:8
main.main()
	/Users/khr/tmp6.go:13 +0xc

This looks like a regression in #33724. It was fine in 1.24.13, but broken in 1.25.0 and since.

A subtler case, where the dereference is implicit in the conversion from *T to *U:

type T struct {
	U
}
type U struct {
	x int
}

func (u *U) setX() {
	u.x = 7
}

func main() {
	var t *T
	t.setX()
}

[randall77]

Probably caused by CL 659317.

[Jorropo]

Bisected to 8af3224

git bisect log

git bisect start
# status: waiting for both good and bad commits
# good: [96e4e2b1616c3c59577d48abcf2823bf1fdcd2e2] [release-branch.go1.24] go1.24.13
git bisect good 96e4e2b1616c3c59577d48abcf2823bf1fdcd2e2
# status: waiting for bad commit, 1 good commit known
# bad: [7bd807271cf4ee370b1a2499e863c4fcb6bf7301] regexp: apply canonicalization to scripts lookup
git bisect bad 7bd807271cf4ee370b1a2499e863c4fcb6bf7301
# good: [37f27fbecd422da9fefb8ae1cc601bc5b4fec44b] cmd/go: enable fips test and fix caching bug
git bisect good 37f27fbecd422da9fefb8ae1cc601bc5b4fec44b
# bad: [86b4fe31d9b7fe4b249a3a8007290305eaa4f16a] [dev.simd] cmd/compile: add masked merging ops and optimizations
git bisect bad 86b4fe31d9b7fe4b249a3a8007290305eaa4f16a
# bad: [ab7f839280df8734c388046f957f7f37ae5b0998] [dev.simd] cmd/compile: fix maskreg/simdreg chaos
git bisect bad ab7f839280df8734c388046f957f7f37ae5b0998
# good: [5715d735590cf545f03b34e58ade83b919e53fba] all: use strings.ReplaceAll where applicable
git bisect good 5715d735590cf545f03b34e58ade83b919e53fba
# bad: [78e86297f5cccb82a6a57081947fab8e8af32586] cmd/compile/internal/noder: rename RelIndex to match codebase
git bisect bad 78e86297f5cccb82a6a57081947fab8e8af32586
# bad: [195e64232d6a799c43b18b02bd7ff24d6bc11c48] cmd/compile/internal/noder: format grammar
git bisect bad 195e64232d6a799c43b18b02bd7ff24d6bc11c48
# bad: [4e63ae46e097062b72424b2ac1da6e7dac33064b] internal/runtime/maps: make clear also erase tombstones
git bisect bad 4e63ae46e097062b72424b2ac1da6e7dac33064b
# bad: [67e0681aef41cfd9794d3f7819450acd08a67905] cmd/compile: put constant value on node inside parentheses
git bisect bad 67e0681aef41cfd9794d3f7819450acd08a67905
# bad: [8af32240c6c8f21695cdcb3b6df8293d7f2d3bc7] cmd/compile: don't evaluate side effects of range over array
git bisect bad 8af32240c6c8f21695cdcb3b6df8293d7f2d3bc7
# good: [a11643df8ff8a575abe4abc7f25d09631424ea49] math/big: replace addVW/subVW assembly with fast pure Go
git bisect good a11643df8ff8a575abe4abc7f25d09631424ea49
# good: [04a9b16f3d69aa66f3aaab44dcd322e4a02a82aa] cmd/compile/internal/escape: avoid reading ir.Node during inner loop of walkOne
git bisect good 04a9b16f3d69aa66f3aaab44dcd322e4a02a82aa
# first bad commit: [8af32240c6c8f21695cdcb3b6df8293d7f2d3bc7] cmd/compile: don't evaluate side effects of range over array

[gopherbot]

Change https://go.dev/cl/785440 mentions this issue: cmd/compile: use position of nil check when merging it with subsequent store

[gabyhelp]

Related Issues

• cmd/compile: bad traceback arguments #45728 (closed)
• cmd/compile: incorrect stack trace for nil dereference in inlined function #27201 (closed)
• cmd/compile: nil pointer dereference for receivers has wrong line number #16462 (closed)
• go/compile: Panics involving defer statements do not consistently display line with defer in stack traces #69761 (closed)
• cmd/compile: misleading stack trace related to struct embedding. #33724 (closed)
• cmd/compile: late nilcheck elim doesn't elim later nilcheck #20962
• runtime: inlined function doesn't appear in stack trace #10152 (closed)

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