cmd/internal/gc: Toughen escape analysis against some bugs.

Ensures that parameter flow bits are not set for tags EscScope, EscHeap, EscNever;
crash the compiler earl to expose faulty logic, rather than flake out silently downstream.

Change-Id: I1428129980ae047d02975f033d56cbbd04f49579
Reviewed-on: https://go-review.googlesource.com/9601
Reviewed-by: Russ Cox <rsc@golang.org>

diff --git a/src/cmd/internal/gc/esc.go b/src/cmd/internal/gc/esc.go
index 044bb3d31d5274db66cba5e98d1513e568cc1cdd..c816feaa7f1151bc0b463b53fb8c73dbed432fd5 100644 (file)
--- a/src/cmd/internal/gc/esc.go
+++ b/src/cmd/internal/gc/esc.go
@@ -343,12 +343,11 @@ const (
 // escMax returns the maximum of an existing escape value
 // (and its additional parameter flow flags) and a new escape type.
 func escMax(e, etype uint16) uint16 {
-       if e&EscMask == EscHeap {
+       if e&EscMask >= EscScope {
                // normalize
-               if e != EscHeap {
-                       Fatal("Escape information had tag bits combined with 'EscHeap' ")
+               if e&^EscMask != 0 {
+                       Fatal("Escape information had unexpected return encoding bits (w/ EscScope, EscHeap, EscNever), e&EscMask=%v", e&EscMask)
                }
-               return EscHeap
        }
        if e&EscMask > etype {
                return e
@@ -1563,7 +1562,7 @@ func escwalk(e *EscState, level Level, dst *Node, src *Node) {
 
        // Input parameter flowing to output parameter?
        var leaks bool
-       if funcOutputAndInput(dst, src) && src.Esc&EscMask != EscScope && src.Esc != EscHeap && dst.Esc != EscHeap {
+       if funcOutputAndInput(dst, src) && src.Esc&EscMask < EscScope && dst.Esc != EscHeap {
                // This case handles:
                // 1. return in
                // 2. return &in
@@ -1586,7 +1585,7 @@ func escwalk(e *EscState, level Level, dst *Node, src *Node) {
        // If parameter content escapes to heap, set EscContentEscapes
        // Note minor confusion around escape from pointer-to-struct vs escape from struct
        if dst.Esc == EscHeap &&
-               src.Op == ONAME && src.Class == PPARAM && src.Esc != EscHeap &&
+               src.Op == ONAME && src.Class == PPARAM && src.Esc&EscMask < EscScope &&
                level.int() > 0 {
                src.Esc = escMax(EscContentEscapes|src.Esc, EscNone)
                if Debug['m'] != 0 {
@@ -1598,7 +1597,7 @@ func escwalk(e *EscState, level Level, dst *Node, src *Node) {
 
        switch src.Op {
        case ONAME:
-               if src.Class == PPARAM && (leaks || dst.Escloopdepth < 0) && src.Esc != EscHeap {
+               if src.Class == PPARAM && (leaks || dst.Escloopdepth < 0) && src.Esc&EscMask < EscScope {
                        if level.guaranteedDereference() > 0 {
                                src.Esc = escMax(EscContentEscapes|src.Esc, EscNone)
                                if Debug['m'] != 0 {