cmd/compile: fix miscompilation of "defer delete(m, k)"

Previously, for slow map key types (i.e., any type other than a 32-bit
or 64-bit plain memory type), we would rewrite

    defer delete(m, k)

into

    ktmp := k
    defer delete(m, &ktmp)

However, if the defer statement was inside a loop, we would end up
reusing the same ktmp value for all of the deferred deletes.

We already rewrite

    defer print(x, y, z)

into

    defer func(a1, a2, a3) {
        print(a1, a2, a3)
    }(x, y, z)

This CL generalizes this rewrite to also apply for slow map deletes.

This could be extended to apply even more generally to other builtins,
but as discussed on #24259, there are cases where we must *not* do
this (e.g., "defer recover()"). However, if we elect to do this more
generally, this CL should still make that easier.

Lastly, while here, fix a few isues in wrapCall (nee walkprintfunc):

1) lookupN appends the generation number to the symbol anyway, so "%d"
was being literally included in the generated function names.

2) walkstmt will be called when the function is compiled later anyway,
so no need to do it now.

Fixes #24259.

Change-Id: I70286867c64c69c18e9552f69e3f4154a0fc8b04
Reviewed-on: https://go-review.googlesource.com/99017
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/runtime/map_test.go b/src/runtime/map_test.go
index b12b09eeb6..d1b268bda4 100644
--- a/src/runtime/map_test.go
+++ b/src/runtime/map_test.go
@@ -875,3 +875,24 @@ func BenchmarkMapDelete(b *testing.B) {
 	b.Run("Int64", runWith(benchmarkMapDeleteInt64, 100, 1000, 10000))
 	b.Run("Str", runWith(benchmarkMapDeleteStr, 100, 1000, 10000))
 }
+
+func TestDeferDeleteSlow(t *testing.T) {
+	ks := []complex128{0, 1, 2, 3}
+
+	m := make(map[interface{}]int)
+	for i, k := range ks {
+		m[k] = i
+	}
+	if len(m) != len(ks) {
+		t.Errorf("want %d elements, got %d", len(ks), len(m))
+	}
+
+	func() {
+		for _, k := range ks {
+			defer delete(m, k)
+		}
+	}()
+	if len(m) != 0 {
+		t.Errorf("want 0 elements, got %d", len(m))
+	}
+}