From 31d13f479a19ca6e07ad60c441298c6eca04eeb2 Mon Sep 17 00:00:00 2001 From: Keith Randall Date: Tue, 8 Mar 2016 20:09:48 -0800 Subject: [PATCH] cmd/compile: don't use PPARAMOUT names for temps The location of VARDEFs is incorrect for PPARAMOUT variables which are also used as temporary locations. We put in VARDEFs when setting the variable at return time, but when the location is also used as a temporary the lifetime values are wrong. Fix copyelim to update the names map properly. This is a real name bug fix which, as a result, allows me to write a reasonable test to trigger the PPARAMOUT bug. This is kind of a band-aid fix for #14591. A more pricipled fix (which allows values to be stored in the return variable earlier than the return point) will be harder. Fixes #14591 Change-Id: I7df8ae103a982d1f218ed704c080d7b83cdcfdd9 Reviewed-on: https://go-review.googlesource.com/20457 Reviewed-by: Josh Bleecher Snyder --- src/cmd/compile/internal/gc/ssa.go | 5 ++++ src/cmd/compile/internal/ssa/copyelim.go | 2 +- test/fixedbugs/issue14591.go | 38 ++++++++++++++++++++++++ 3 files changed, 44 insertions(+), 1 deletion(-) create mode 100644 test/fixedbugs/issue14591.go diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go index afba7db638..87d2374216 100644 --- a/src/cmd/compile/internal/gc/ssa.go +++ b/src/cmd/compile/internal/gc/ssa.go @@ -3608,6 +3608,11 @@ func (s *state) addNamedValue(n *Node, v *ssa.Value) { // pseudos in the right place when we spill to these nodes. return } + if n.Class == PPARAMOUT { + // Don't track named output values. This prevents return values + // from being assigned too early. See #14591 and #14762. TODO: allow this. + return + } if n.Class == PAUTO && n.Xoffset != 0 { s.Fatalf("AUTO var with offset %s %d", n, n.Xoffset) } diff --git a/src/cmd/compile/internal/ssa/copyelim.go b/src/cmd/compile/internal/ssa/copyelim.go index cfeff21e84..5488134122 100644 --- a/src/cmd/compile/internal/ssa/copyelim.go +++ b/src/cmd/compile/internal/ssa/copyelim.go @@ -28,7 +28,7 @@ func copyelim(f *Func) { x = x.Args[0] } if x != v { - values[i] = v + values[i] = x } } } diff --git a/test/fixedbugs/issue14591.go b/test/fixedbugs/issue14591.go new file mode 100644 index 0000000000..e4fa80af50 --- /dev/null +++ b/test/fixedbugs/issue14591.go @@ -0,0 +1,38 @@ +// run + +// Copyright 2016 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. + +// Test to make sure we don't think values are dead +// when they are assigned to a PPARAMOUT slot before +// the last GC safepoint. + +package main + +import ( + "fmt" + "runtime" +) + +// When a T is deallocated, T[1] is certain to +// get clobbered (the runtime writes 0xdeaddeaddeaddead there). +type T [4]int + +func f() (r, s *T) { + r = &T{0x30, 0x31, 0x32, 0x33} + runtime.GC() + s = &T{0x40, 0x41, 0x42, 0x43} + runtime.GC() + return +} + +func main() { + r, s := f() + if r[1] != 0x31 { + fmt.Printf("bad r[1], want 0x31 got %x\n", r[1]) + } + if s[1] != 0x41 { + fmt.Printf("bad s[1], want 0x41 got %x\n", s[1]) + } +} -- 2.48.1