From 61336b78c18e90d90d68c5c2ce61d8d530669ed1 Mon Sep 17 00:00:00 2001 From: Josh Bleecher Snyder Date: Fri, 5 May 2017 15:22:59 -0700 Subject: [PATCH] cmd/compile: don't update outer variables after capturevars is complete When compiling concurrently, we walk all functions before compiling any of them. Walking functions can cause variables to switch from being non-addrtaken to addrtaken, e.g. to prepare for a runtime call. Typechecking propagates addrtaken-ness of closure variables to their outer variables, so that capturevars can decide whether to pass the variable's value or a pointer to it. When all functions are compiled immediately, as long as the containing function is compiled prior to the closure, this propagation has no effect. When compilation is deferred, though, in rare cases, this results in a change in the addrtaken-ness of a variable in the outer function, which in turn changes the compiler's output. (This is rare because in a great many cases, a temporary has been introduced, insulating the outer variable from modification.) But concurrent compilation must generate identical results. To fix this, track whether capturevars has run. If it has, there is no need to update outer variables when closure variables change. Capturevars always runs before any functions are walked or compiled. The remainder of the changes in this CL are to support the test. In particular, -d=compilelater forces the compiler to walk all functions before compiling any of them, despite being non-concurrent. This is useful because -live is fundamentally incompatible with concurrent compilation, but we want -c=1 to have no behavior changes. Fixes #20250 Change-Id: I89bcb54268a41e8588af1ac8cc37fbef856a90c2 Reviewed-on: https://go-review.googlesource.com/42853 Run-TryBot: Josh Bleecher Snyder TryBot-Result: Gobot Gobot Reviewed-by: Robert Griesemer --- src/cmd/compile/internal/gc/closure.go | 3 +++ src/cmd/compile/internal/gc/main.go | 21 ++++++++++++--------- src/cmd/compile/internal/gc/pgen.go | 2 +- src/cmd/compile/internal/gc/typecheck.go | 9 +++++++-- test/fixedbugs/issue20250.go | 24 ++++++++++++++++++++++++ 5 files changed, 47 insertions(+), 12 deletions(-) create mode 100644 test/fixedbugs/issue20250.go diff --git a/src/cmd/compile/internal/gc/closure.go b/src/cmd/compile/internal/gc/closure.go index 50d679ea97..04f3e669e2 100644 --- a/src/cmd/compile/internal/gc/closure.go +++ b/src/cmd/compile/internal/gc/closure.go @@ -243,6 +243,9 @@ func makeclosure(func_ *Node) *Node { return xfunc } +// capturevarscomplete is set to true when the capturevars phase is done. +var capturevarscomplete bool + // capturevars is called in a separate phase after all typechecking is done. // It decides whether each variable captured by a closure should be captured // by value or by reference. diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go index f67822e613..a2472fa08b 100644 --- a/src/cmd/compile/internal/gc/main.go +++ b/src/cmd/compile/internal/gc/main.go @@ -33,15 +33,16 @@ var ( ) var ( - Debug_append int - Debug_asm bool - Debug_closure int - debug_dclstack int - Debug_panic int - Debug_slice int - Debug_vlog bool - Debug_wb int - Debug_pctab string + Debug_append int + Debug_asm bool + Debug_closure int + Debug_compilelater int + debug_dclstack int + Debug_panic int + Debug_slice int + Debug_vlog bool + Debug_wb int + Debug_pctab string ) // Debug arguments. @@ -56,6 +57,7 @@ var debugtab = []struct { }{ {"append", "print information about append compilation", &Debug_append}, {"closure", "print information about closure compilation", &Debug_closure}, + {"compilelater", "compile functions as late as possible", &Debug_compilelater}, {"disablenil", "disable nil checks", &disable_checknil}, {"dclstack", "run internal dclstack check", &debug_dclstack}, {"gcprog", "print dump of GC programs", &Debug_gcprog}, @@ -493,6 +495,7 @@ func Main(archInit func(*Arch)) { capturevars(n) } } + capturevarscomplete = true Curfn = nil diff --git a/src/cmd/compile/internal/gc/pgen.go b/src/cmd/compile/internal/gc/pgen.go index 91cd1e35d7..fdf3bf7847 100644 --- a/src/cmd/compile/internal/gc/pgen.go +++ b/src/cmd/compile/internal/gc/pgen.go @@ -226,7 +226,7 @@ func compile(fn *Node) { // they are enqueued in compilequeue, // which is drained by compileFunctions. func compilenow() bool { - return nBackendWorkers == 1 + return nBackendWorkers == 1 && Debug_compilelater == 0 } // compileSSA builds an SSA backend function, diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go index 5e92e926e3..b02bc659be 100644 --- a/src/cmd/compile/internal/gc/typecheck.go +++ b/src/cmd/compile/internal/gc/typecheck.go @@ -815,7 +815,11 @@ OpSwitch: var l *Node for l = n.Left; l != r; l = l.Left { l.SetAddrtaken(true) - if l.IsClosureVar() { + if l.IsClosureVar() && !capturevarscomplete { + // Mark the original variable as Addrtaken so that capturevars + // knows not to pass it by value. + // But if the capturevars phase is complete, don't touch it, + // in case l.Name's containing function has not yet been compiled. l.Name.Defn.SetAddrtaken(true) } } @@ -824,7 +828,8 @@ OpSwitch: Fatalf("found non-orig name node %v", l) } l.SetAddrtaken(true) - if l.IsClosureVar() { + if l.IsClosureVar() && !capturevarscomplete { + // See comments above about closure variables. l.Name.Defn.SetAddrtaken(true) } n.Left = defaultlit(n.Left, nil) diff --git a/test/fixedbugs/issue20250.go b/test/fixedbugs/issue20250.go new file mode 100644 index 0000000000..f24710a0c3 --- /dev/null +++ b/test/fixedbugs/issue20250.go @@ -0,0 +1,24 @@ +// errorcheck -0 -live -d=compilelater + +// Copyright 2017 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Issue 20250: liveness differed with concurrent compilation +// due to propagation of addrtaken to outer variables for +// closure variables. + +package p + +type T struct { + s string +} + +func f(a T) { // ERROR "live at entry to f: a" + var e interface{} + func() { // ERROR "live at entry to f.func1: &e a" + e = a.s // ERROR "live at call to convT2Estring: &e a" "live at call to writebarrierptr: a" + }() // ERROR "live at call to f.func1: e$" + // Before the fix, both a and e were live at the previous line. + _ = e +} -- 2.50.0