From 39986d28e435d23e1d1dc41b8f16c0cf30181208 Mon Sep 17 00:00:00 2001 From: Than McIntosh Date: Tue, 4 Apr 2023 18:31:46 -0400 Subject: [PATCH] cmd/compile: allow more inlining of functions that construct closures MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit [This is a roll-forward of CL 479095, which was reverted due to a bad interaction between inlining and escape analysis since fixed in CL 482355.] Currently, when the inliner is determining if a function is inlineable, it descends into the bodies of closures constructed by that function. This has several unfortunate consequences: - If the closure contains a disallowed operation (e.g., a defer), then the outer function can't be inlined. It makes sense that the *closure* can't be inlined in this case, but it doesn't make sense to punish the function that constructs the closure. - The hairiness of the closure counts against the inlining budget of the outer function. Since we currently copy the closure body when inlining the outer function, this makes sense from the perspective of export data size and binary size, but ultimately doesn't make much sense from the perspective of what should be inlineable. - Since the inliner walks into every closure created by an outer function in addition to starting a walk at every closure, this adds an n^2 factor to inlinability analysis. This CL simply drops this behavior. In std, this makes 57 more functions inlinable, and disallows inlining for 10 (due to the basic instability of our bottom-up inlining approach), for an net increase of 47 inlinable functions (+0.6%). This will help significantly with the performance of the functions to be added for #56102, which have a somewhat complicated nesting of closures with a performance-critical fast path. The downside of this seems to be a potential increase in export data and text size, but the practical impact of this seems to be negligible: │ before │ after │ │ bytes │ bytes vs base │ Go/binary 15.12Mi ± 0% 15.14Mi ± 0% +0.16% (n=1) Go/text 5.220Mi ± 0% 5.237Mi ± 0% +0.32% (n=1) Compile/binary 22.92Mi ± 0% 22.94Mi ± 0% +0.07% (n=1) Compile/text 8.428Mi ± 0% 8.435Mi ± 0% +0.08% (n=1) Updates #56102. Change-Id: I1f4fc96c71609c8feb59fecdb92b69ba7e3b5b41 Reviewed-on: https://go-review.googlesource.com/c/go/+/482356 Reviewed-by: Cuong Manh Le Run-TryBot: Than McIntosh Reviewed-by: Cherry Mui TryBot-Result: Gopher Robot --- src/cmd/compile/internal/inline/inl.go | 11 +++++----- src/cmd/compile/internal/test/inl_test.go | 22 ++++++++----------- test/closure3.dir/main.go | 26 +++++++++++++---------- 3 files changed, 29 insertions(+), 30 deletions(-) diff --git a/src/cmd/compile/internal/inline/inl.go b/src/cmd/compile/internal/inline/inl.go index 3b42818c57..3e4498eff5 100644 --- a/src/cmd/compile/internal/inline/inl.go +++ b/src/cmd/compile/internal/inline/inl.go @@ -459,6 +459,8 @@ func (v *hairyVisitor) tooHairy(fn *ir.Func) bool { return false } +// doNode visits n and its children, updates the state in v, and returns true if +// n makes the current function too hairy for inlining. func (v *hairyVisitor) doNode(n ir.Node) bool { if n == nil { return false @@ -590,13 +592,10 @@ func (v *hairyVisitor) doNode(n ir.Node) bool { // TODO(danscales): Maybe make budget proportional to number of closure // variables, e.g.: //v.budget -= int32(len(n.(*ir.ClosureExpr).Func.ClosureVars) * 3) + // TODO(austin): However, if we're able to inline this closure into + // v.curFunc, then we actually pay nothing for the closure captures. We + // should try to account for that if we're going to account for captures. v.budget -= 15 - // Scan body of closure (which DoChildren doesn't automatically - // do) to check for disallowed ops in the body and include the - // body in the budget. - if doList(n.(*ir.ClosureExpr).Func.Body, v.do) { - return true - } case ir.OGO, ir.ODEFER, diff --git a/src/cmd/compile/internal/test/inl_test.go b/src/cmd/compile/internal/test/inl_test.go index 2a16b21cef..205b746dd8 100644 --- a/src/cmd/compile/internal/test/inl_test.go +++ b/src/cmd/compile/internal/test/inl_test.go @@ -180,19 +180,15 @@ func TestIntendedInlining(t *testing.T) { "net": { "(*UDPConn).ReadFromUDP", }, - // These testpoints commented out for now, since CL 479095 - // had to be reverted. We can re-enable this once we roll - // forward with a new version of 479095. - /* - "sync": { - // Both OnceFunc and its returned closure need to be inlinable so - // that the returned closure can be inlined into the caller of OnceFunc. - "OnceFunc", - "OnceFunc.func2", // The returned closure. - // TODO(austin): It would be good to check OnceValue and OnceValues, - // too, but currently they aren't reported because they have type - // parameters and aren't instantiated in sync. - }, */ + "sync": { + // Both OnceFunc and its returned closure need to be inlinable so + // that the returned closure can be inlined into the caller of OnceFunc. + "OnceFunc", + "OnceFunc.func2", // The returned closure. + // TODO(austin): It would be good to check OnceValue and OnceValues, + // too, but currently they aren't reported because they have type + // parameters and aren't instantiated in sync. + }, "sync/atomic": { // (*Bool).CompareAndSwap handled below. "(*Bool).Load", diff --git a/test/closure3.dir/main.go b/test/closure3.dir/main.go index 4d02a4d10e..04a669206e 100644 --- a/test/closure3.dir/main.go +++ b/test/closure3.dir/main.go @@ -232,15 +232,15 @@ func main() { { c := 3 - func() { // ERROR "func literal does not escape" + func() { // ERROR "can inline main.func26" c = 4 - func() { // ERROR "func literal does not escape" + func() { if c != 4 { ppanic("c != 4") } recover() // prevent inlining }() - }() + }() // ERROR "inlining call to main.func26" "func literal does not escape" if c != 4 { ppanic("c != 4") } @@ -248,33 +248,37 @@ func main() { { a := 2 - if r := func(x int) int { // ERROR "func literal does not escape" + // This has an unfortunate exponential growth, where as we visit each + // function, we inline the inner closure, and that constructs a new + // function for any closures inside the inner function, and then we + // revisit those. E.g., func34 and func36 are constructed by the inliner. + if r := func(x int) int { // ERROR "can inline main.func27" b := 3 - return func(y int) int { // ERROR "can inline main.func27.1" + return func(y int) int { // ERROR "can inline main.func27.1" "can inline main.func34" c := 5 - return func(z int) int { // ERROR "can inline main.func27.1.1" "can inline main.func27.(func)?2" + return func(z int) int { // ERROR "can inline main.func27.1.1" "can inline main.func27.(func)?2" "can inline main.func34.1" "can inline main.func36" return a*x + b*y + c*z }(10) // ERROR "inlining call to main.func27.1.1" }(100) // ERROR "inlining call to main.func27.1" "inlining call to main.func27.(func)?2" - }(1000); r != 2350 { + }(1000); r != 2350 { // ERROR "inlining call to main.func27" "inlining call to main.func34" "inlining call to main.func36" ppanic("r != 2350") } } { a := 2 - if r := func(x int) int { // ERROR "func literal does not escape" + if r := func(x int) int { // ERROR "can inline main.func28" b := 3 - return func(y int) int { // ERROR "can inline main.func28.1" + return func(y int) int { // ERROR "can inline main.func28.1" "can inline main.func35" c := 5 - func(z int) { // ERROR "can inline main.func28.1.1" "can inline main.func28.(func)?2" + func(z int) { // ERROR "can inline main.func28.1.1" "can inline main.func28.(func)?2" "can inline main.func35.1" "can inline main.func37" a = a * x b = b * y c = c * z }(10) // ERROR "inlining call to main.func28.1.1" return a + c }(100) + b // ERROR "inlining call to main.func28.1" "inlining call to main.func28.(func)?2" - }(1000); r != 2350 { + }(1000); r != 2350 { // ERROR "inlining call to main.func28" "inlining call to main.func35" "inlining call to main.func37" ppanic("r != 2350") } if a != 2000 {