cmd/compile: expand large stack frame error messages

Change-Id: Ib9f621e380dd9a6beace27ec5ff62780012f8274
Reviewed-on: https://go-review.googlesource.com/c/144600
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/main.go

@@ -689,10 +689,14 @@ func Main(archInit func(*Arch)) {
 
 	// Check whether any of the functions we have compiled have gigantic stack frames.
 	obj.SortSlice(largeStackFrames, func(i, j int) bool {
-		return largeStackFrames[i].Before(largeStackFrames[j])
+		return largeStackFrames[i].pos.Before(largeStackFrames[j].pos)
 	})
-	for _, largePos := range largeStackFrames {
+	for _, large := range largeStackFrames {
-		yyerrorl(largePos, "stack frame too large (>1GB)")
+		if large.callee != 0 {
+			yyerrorl(large.pos, "stack frame too large (>1GB): %d MB locals + %d MB args + %d MB callee", large.locals>>20, large.args>>20, large.callee>>20)
+		} else {
+			yyerrorl(large.pos, "stack frame too large (>1GB): %d MB locals + %d MB args", large.locals>>20, large.args>>20)
+		}
 	}
 
 	if len(compilequeue) != 0 {

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

@@ -279,7 +279,7 @@ func compileSSA(fn *Node, worker int) {
 	// Note: check arg size to fix issue 25507.
 	if f.Frontend().(*ssafn).stksize >= maxStackSize || fn.Type.ArgWidth() >= maxStackSize {
 		largeStackFramesMu.Lock()
-		largeStackFrames = append(largeStackFrames, fn.Pos)
+		largeStackFrames = append(largeStackFrames, largeStack{locals: f.Frontend().(*ssafn).stksize, args: fn.Type.ArgWidth(), pos: fn.Pos})
 		largeStackFramesMu.Unlock()
 		return
 	}
@@ -294,7 +294,8 @@ func compileSSA(fn *Node, worker int) {
 	// the assembler may emit inscrutable complaints about invalid instructions.
 	if pp.Text.To.Offset >= maxStackSize {
 		largeStackFramesMu.Lock()
-		largeStackFrames = append(largeStackFrames, fn.Pos)
+		locals := f.Frontend().(*ssafn).stksize
+		largeStackFrames = append(largeStackFrames, largeStack{locals: locals, args: fn.Type.ArgWidth(), callee: pp.Text.To.Offset - locals, pos: fn.Pos})
 		largeStackFramesMu.Unlock()
 		return
 	}

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

@@ -28,9 +28,17 @@ type Error struct {
 
 var errors []Error
 
+// largeStack is info about a function whose stack frame is too large (rare).
+type largeStack struct {
+	locals int64
+	args   int64
+	callee int64
+	pos    src.XPos
+}
+
 var (
 	largeStackFramesMu sync.Mutex // protects largeStackFrames
-	largeStackFrames   []src.XPos // positions of functions whose stack frames are too large (rare)
+	largeStackFrames   []largeStack
 )
 
 func errorexit() {