From: Russ Cox <rsc@golang.org>
Date: Fri, 14 Feb 2014 05:38:24 +0000 (-0500)
Subject: cmd/gc: correct liveness for various non-returning functions
X-Git-Tag: go1.3beta1~701
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=af545660d59edeffb52b8b72bec08f8c7b33cf23;p=gostls13.git

cmd/gc: correct liveness for various non-returning functions

When the liveness code doesn't know a function doesn't return
(but the generated code understands that), the liveness analysis
invents a control flow edge that is not really there, which can cause
variables to seem spuriously live. This is particularly bad when the
variables are uninitialized.

TBR=iant
CC=golang-codereviews
https://golang.org/cl/63720043
---

diff --git a/src/cmd/gc/popt.c b/src/cmd/gc/popt.c
index 7fcf5db10d..1f0bdb496a 100644
--- a/src/cmd/gc/popt.c
+++ b/src/cmd/gc/popt.c
@@ -51,6 +51,9 @@ noreturn(Prog *p)
 		symlist[2] = pkglookup("throwinit", runtimepkg);
 		symlist[3] = pkglookup("panic", runtimepkg);
 		symlist[4] = pkglookup("panicwrap", runtimepkg);
+		symlist[5] = pkglookup("throwreturn", runtimepkg);
+		symlist[6] = pkglookup("selectgo", runtimepkg);
+		symlist[7] = pkglookup("block", runtimepkg);
 	}
 
 	if(p->to.node == nil)
diff --git a/test/live.go b/test/live.go
index 032d39812d..9c4e754c17 100644
--- a/test/live.go
+++ b/test/live.go
@@ -121,3 +121,64 @@ func f10() string {
 	panic(1)
 }
 
+// liveness formerly confused by select, thinking runtime.selectgo
+// can return to next instruction; it always jumps elsewhere.
+// note that you have to use at least two cases in the select
+// to get a true select; smaller selects compile to optimized helper functions.
+
+var c chan *int
+var b bool
+
+// this used to have a spurious "live at entry to f11a: ~r0"
+func f11a() *int {
+	select { // ERROR "live at call to selectgo: autotmp"
+	case <-c: // ERROR "live at call to selectrecv: autotmp"
+		return nil
+	case <-c: // ERROR "live at call to selectrecv: autotmp"
+		return nil
+	}
+}
+
+func f11b() *int {
+	p := new(int)
+	if b {
+		// At this point p is dead: the code here cannot
+		// get to the bottom of the function.
+		// This used to have a spurious "live at call to printint: p".
+		print(1) // nothing live here!
+		select { // ERROR "live at call to selectgo: autotmp"
+		case <-c: // ERROR "live at call to selectrecv: autotmp"
+			return nil
+		case <-c: // ERROR "live at call to selectrecv: autotmp"
+			return nil
+		}
+	}
+	println(*p)
+	return nil
+}
+
+func f11c() *int {
+	p := new(int)
+	if b {
+		// Unlike previous, the cases in this select fall through,
+		// so we can get to the println, so p is not dead.
+		print(1) // ERROR "live at call to printint: p"
+		select { // ERROR "live at call to newselect: p" "live at call to selectgo: autotmp.* p"
+		case <-c: // ERROR "live at call to selectrecv: autotmp.* p"
+		case <-c: // ERROR "live at call to selectrecv: autotmp.* p"
+		}
+	}
+	println(*p)
+	return nil
+}
+
+// similarly, select{} does not fall through.
+// this used to have a spurious "live at entry to f12: ~r0".
+
+func f12() *int {
+	if b {
+		select{}
+	} else {
+		return nil
+	}
+}