runtime: support runtime.freegc in size-specialized mallocs for noscan objects

This CL is part of a set of CLs that attempt to reduce how much work the
GC must do. See the design in https://go.dev/design/74299-runtime-freegc

This CL updates the smallNoScanStub stub in malloc_stubs.go to reuse
heap objects that have been freed by runtime.freegc calls, and generates
the corresponding size-specialized code in malloc_generated.go.

This CL only adds support in the specialized mallocs for noscan
heap objects (objects without pointers). A later CL handles objects
with pointers.

While we are here, we leave a couple of breadcrumbs in mkmalloc.go on
how to do the generation.

Updates #74299

Change-Id: I2657622601a27211554ee862fce057e101767a70
Reviewed-on: https://go-review.googlesource.com/c/go/+/715761
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

1 files changed, 10 insertions, 6 deletions

diff --git a/src/runtime/malloc_test.go b/src/runtime/malloc_test.go
index 10c20e6c23..97cf0eed54 100644
--- a/src/runtime/malloc_test.go
+++ b/src/runtime/malloc_test.go
@@ -349,8 +349,10 @@ func testFreegc[T comparable](noscan bool) func(*testing.T) {
 		t.Run("allocs-with-free", func(t *testing.T) {
 			// Same allocations, but now using explicit free so that
 			// no allocs get reported. (Again, not the desired long-term behavior).
-			if SizeSpecializedMallocEnabled {
-				t.Skip("temporarily skipping alloc tests for GOEXPERIMENT=sizespecializedmalloc")
+			if SizeSpecializedMallocEnabled && !noscan {
+				// TODO(thepudds): skip at this point in the stack for size-specialized malloc
+				// with !noscan. Additional integration with sizespecializedmalloc is in a later CL.
+				t.Skip("temporarily skipping alloc tests for GOEXPERIMENT=sizespecializedmalloc for pointer types")
 			}
 			if !RuntimeFreegcEnabled {
 				t.Skip("skipping alloc tests with runtime.freegc disabled")
@@ -370,8 +372,10 @@ func testFreegc[T comparable](noscan bool) func(*testing.T) {
 			// Multiple allocations outstanding before explicitly freeing,
 			// but still within the limit of our smallest free list size
 			// so that no allocs are reported. (Again, not long-term behavior).
-			if SizeSpecializedMallocEnabled {
-				t.Skip("temporarily skipping alloc tests for GOEXPERIMENT=sizespecializedmalloc")
+			if SizeSpecializedMallocEnabled && !noscan {
+				// TODO(thepudds): skip at this point in the stack for size-specialized malloc
+				// with !noscan. Additional integration with sizespecializedmalloc is in a later CL.
+				t.Skip("temporarily skipping alloc tests for GOEXPERIMENT=sizespecializedmalloc for pointer types")
 			}
 			if !RuntimeFreegcEnabled {
 				t.Skip("skipping alloc tests with runtime.freegc disabled")
@@ -514,10 +518,10 @@ func testFreegc[T comparable](noscan bool) func(*testing.T) {
 			// See https://go.dev/cl/717520 for some additional discussion,
 			// including how we can deliberately cause the test to fail currently
 			// if we purposefully introduce some assist credit bugs.
-			if SizeSpecializedMallocEnabled {
+			if SizeSpecializedMallocEnabled && !noscan {
 				// TODO(thepudds): skip this test at this point in the stack; later CL has
 				// integration with sizespecializedmalloc.
-				t.Skip("temporarily skip assist credit test for GOEXPERIMENT=sizespecializedmalloc")
+				t.Skip("temporarily skip assist credit tests for GOEXPERIMENT=sizespecializedmalloc for pointer types")
 			}
 			if !RuntimeFreegcEnabled {
 				t.Skip("skipping assist credit test with runtime.freegc disabled")