cmd/compile: don't generate liveness maps when the stack is too large

Fixes #20529

Change-Id: I3cb0c037b1737fbc3fa3b1b61ed8a42cfaf8e10d
Reviewed-on: https://go-review.googlesource.com/44344
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/gc/pgen.go

@@ -230,6 +230,8 @@ func compilenow() bool {
 	return nBackendWorkers == 1 && Debug_compilelater == 0
 }
 
+const maxStackSize = 1 << 31
+
 // compileSSA builds an SSA backend function,
 // uses it to generate a plist,
 // and flushes that plist to machine code.
@@ -238,7 +240,7 @@ func compileSSA(fn *Node, worker int) {
 	ssafn := buildssa(fn, worker)
 	pp := newProgs(fn, worker)
 	genssa(ssafn, pp)
-	if pp.Text.To.Offset < 1<<31 {
+	if pp.Text.To.Offset < maxStackSize {
 		pp.Flush()
 	} else {
 		largeStackFramesMu.Lock()

src/cmd/compile/internal/gc/ssa.go

@@ -4373,8 +4373,11 @@ func genssa(f *ssa.Func, pp *Progs) {
 
 	e := f.Frontend().(*ssafn)
 
-	// Generate GC bitmaps.
-	s.stackMapIndex = liveness(e, f)
+	// Generate GC bitmaps, except if the stack is too large,
+	// in which compilation will fail later anyway (issue 20529).
+	if e.stksize < maxStackSize {
+		s.stackMapIndex = liveness(e, f)
+	}
 
 	// Remember where each block starts.
 	s.bstart = make([]*obj.Prog, f.NumBlocks())

src/go/types/stdlib_test.go

@@ -172,6 +172,7 @@ func TestStdFixed(t *testing.T) {
 		"issue18882.go", // go/types doesn't check validity of //go:xxx directives
 		"issue20232.go", // go/types handles larger constants than gc
 		"issue20227.go", // go/types does not handle this yet
+		"issue20529.go", // go/types does not have constraints on stack size
 	)
 }
 

test/fixedbugs/issue20529.go

@@ -0,0 +1,18 @@
+// errorcheck
+
+// +build amd64
+
+// 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 20529: Large stack frames caused compiler panics.
+// Only tested on amd64 because the test only makes sense
+// on a 64 bit system, and it is platform-agnostic,
+// so testing one suffices.
+
+package p
+
+func f() { // ERROR "stack frame too large"
+	_ = [][]int{1e9: []int{}}
+}