proposal: x/tools/go/{ssa,cfg}: expose "no return" API

[adonovan]

Background: The precision of analyses that use the golang.org/x/tools/go/ssa representation of Go programs is improved by exploiting information about which function calls can never return, such as log.Fatal or (*testing.T).Fatalf. This information is already computed interprocedurally by the ctrlflow analyzer, which uses the x/tools/go/cfg package, and is plumbed through to x/tools/go/ssa by using three backdoors. This is implemented in https://go.dev/cl/716920. We would like to add public API to obviate the need for such hacks.

Proposal: We propose to expose these three accessor methods:

package cfg // x/tools/go/cfg

// NoReturn reports whether the control flow graph cannot return normally.
func (*CFG) NoReturn() bool

package ctrlflow // x/tools/go/analysis/passes/ctrlflow

// NoReturn reports whether the specified control-flow graph cannot return normally.
func (*CFGs) NoReturn(*types.Func) bool

package ssa // x/tools/go/ssa

// SetNoReturn sets the predicate used by the SSA builder to decide whether a 
// call to the specified named function cannot return normally.
// This allows the builder to prune infeasible control flow edges,
// improving the precision of downstream analyses.
func (*Program) SetNoReturn(func (*types.Func) bool)

[gopherbot]

Change https://go.dev/cl/716920 mentions this issue: go/ssa: exploit "noreturn" info to prune spurious CFG edges

[gabyhelp]

Related Issues

• proposal: x/tools/go/ssa: add Postdominator to Function/BasicBlock #46942
• x/tools/go/ssa/ssautil: Reachable: conservative approximation to reachable functions, runtime types #69291

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[aclements]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— aclements for the proposal review group