Revert "runtime, cmd/compile: use preemptible memclr for large pointer-free clears"

This reverts CL 750480.

Reason: Adding preemptible memclrNoHeapPointers exposes existing unsafe
use of notInHeapSlice, causing crashes. Revert the memclr stack until
the underlying issue is fixed.

We keep the test added in CL 755942, which is useful regardless.

For #78254.

Change-Id: I8be3f9a20292b7f294e98e74e5a86c6a204406ae
Reviewed-on: https://go-review.googlesource.com/c/go/+/757343
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 0 insertions, 9 deletions

diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index 2144ea602a..c08bc7574b 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -2202,15 +2202,6 @@ func memclrNoHeapPointersChunked(size uintptr, x unsafe.Pointer) {
 	}
 }
 
-// memclrNoHeapPointersPreemptible is the compiler-callable entry point
-// for clearing large buffers with preemption support. It has the same
-// signature as memclrNoHeapPointers so the compiler can emit calls to it
-// directly. It delegates to memclrNoHeapPointersChunked which splits the
-// work into 256KB chunks with preemption checks between them.
-func memclrNoHeapPointersPreemptible(ptr unsafe.Pointer, n uintptr) {
-	memclrNoHeapPointersChunked(n, ptr)
-}
-
 // implementation of new builtin
 // compiler (both frontend and SSA backend) knows the signature
 // of this function.