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cmd/gc: fix &result escaping into result
There is a hierarchy of location defined by loop depth: -1 = the heap 0 = function results 1 = local variables (and parameters) 2 = local variable declared inside a loop 3 = local variable declared inside a loop inside a loop etc In general if an address from loopdepth n is assigned to something in loop depth m < n, that indicates an extended lifetime of some form that requires a heap allocation. Function results can be local variables too, though, and so they don't actually fit into the hierarchy very well. Treat the address of a function result as level 1 so that if it is written back into a result, the address is treated as escaping. Fixes #8185. LGTM=iant R=iant CC=golang-codereviews https://golang.org/cl/108870044
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@ -673,12 +673,21 @@ esc(EscState *e, Node *n, Node *up)
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// for &x, use loop depth of x if known.
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// it should always be known, but if not, be conservative
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// and keep the current loop depth.
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if(n->left->op == ONAME && (n->left->escloopdepth != 0 || n->left->class == PPARAMOUT)) {
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if(n->left->op == ONAME) {
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switch(n->left->class) {
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case PAUTO:
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if(n->left->escloopdepth != 0)
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n->escloopdepth = n->left->escloopdepth;
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break;
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case PPARAM:
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case PPARAMOUT:
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n->escloopdepth = n->left->escloopdepth;
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// PPARAM is loop depth 1 always.
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// PPARAMOUT is loop depth 0 for writes
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// but considered loop depth 1 for address-of,
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// so that writing the address of one result
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// to another (or the same) result makes the
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// first result move to the heap.
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n->escloopdepth = 1;
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break;
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}
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}
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@ -1478,3 +1478,15 @@ func foo153(v interface{}) *int { // ERROR "leaking param: v"
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}
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panic(0)
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}
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// issue 8185 - &result escaping into result
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func f() (x int, y *int) { // ERROR "moved to heap: x"
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y = &x // ERROR "&x escapes to heap"
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return
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}
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func g() (x interface{}) { // ERROR "moved to heap: x"
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x = &x // ERROR "&x escapes to heap"
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return
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}
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