cmd/compile: fix unnamed parameter handling in escape analysis

For recursive functions, the parameters were iterated using
fn.Name.Defn.Func.Dcl, which does not include unnamed/blank
parameters. This results in a mismatch in formal-actual
assignments, for example,

func f(_ T, x T)

f(a, b) should result in { _=a, x=b }, but the escape analysis
currently sees only { x=a } and drops b on the floor. This may
cause b to not escape when it should (or a escape when it should
not).

Fix this by using fntype.Params().FieldSlice() instead, which
does include unnamed parameters.

Also add a sanity check that ensures all the actual parameters
are consumed.

Fixes #29000

Change-Id: Icd86f2b5d71e7ebbab76e375b7702f62efcf59ae
Reviewed-on: https://go-review.googlesource.com/c/152617
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/test/escape5.go b/test/escape5.go
index 03283a37f8..e26ecd5275 100644
--- a/test/escape5.go
+++ b/test/escape5.go
@@ -228,3 +228,20 @@ func f15730c(args ...interface{}) { // ERROR "leaking param content: args"
 		}
 	}
 }
+
+// Issue 29000: unnamed parameter is not handled correctly
+
+var sink4 interface{}
+var alwaysFalse = false
+
+func f29000(_ int, x interface{}) { // ERROR "leaking param: x"
+	sink4 = x
+	if alwaysFalse {
+		g29000()
+	}
+}
+
+func g29000() {
+	x := 1
+	f29000(2, x) // ERROR "x escapes to heap"
+}