commit b74c09864920a69a4d2f6ef0ecb4f9cff226893a
author Alan Donovan <adonovan@google.com> Fri Oct 31 17:14:50 2025 -0400
committer Gopher Robot <gobot@golang.org> Tue Nov 04 14:26:35 2025 -0800
tree 048b14e5a8996c279c4f32402d0e0f78561e99a7
parent 655fb0703cb81c72ef6a6734fc21b7c16ccb8ee0

go/ssa: exploit "noreturn" info to prune spurious CFG edges

This CL causes the buildssa analyzer to exploit interprocedural
"noreturn" information (computed by the ctrlflow analyzer)
when building SSA. This allows it to prune infeasible control-flow
edges after a call that cannot return, such as t.Fatal or log.Fatal,
making the dominator tree deeper and improving the precision of
downstream analysis such as nilness and yield.

For example, nilness can now report cases such as this:

	f, err := os.Open("")
	if err != nil {
		log.Fatal(err) // can't return
	}
	if err != nil { // "impossible condition"
		log.Fatal(err)
	}
	f.Close()

and it now reports 26 (was 20) diagnostics in std.

Similarly, gopls' yield analyzer is now silent where
before it reported a false positive here:

	return func(yield func(int) bool) {
		for {
			if !yield(55) { // "yield may be called again after returning false"
				runtime.Goexit()
			}
		}
	}

Various "internal" hooks were required to expose the three
hidden accessor functions, which are logically equivalent
to these potential future API additions:

 (cfg.CFG).NoReturn() bool
 (*ctrlflow.CFGs).NoReturn(*types.Func) bool
 (*ssa.Program).SetNoReturn(func (*types.Func) bool)

See golang/go#76161 for the proposal.

Change-Id: Ic91572a19f062babd520762dfe6d5749e12d8cd0
Reviewed-on: https://go-review.googlesource.com/c/tools/+/716920
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Markus Kusano <kusano@google.com>