Disable partial overwrite tracking in LLVM 14 DSE via a patch

Starting from LLVM 14, Dead Store Elimination pass tends to perform
`llvm.memset` shortening more often, and upon `memset` resolution, the
resulting "extra" GEP to i8* cannot be consumed by our GEP lowering
optimizations. Bypassing this behavior through an LLVM flag lets our memory
optimizations produce the

Long-term, we should try teaching our `LowerGEPForPrivMem` pass to understand
these shortening sequences and investigate if this partial shortening by DSE
could bring even more performance benefits.

(cherry picked from commit fe18a1b)

Author: Artem Gindinson

external/llvm/releases/14.0.0/patches_external/DSE-disable-partial-overwrite-tracking.patch

@@ -0,0 +1,43 @@
+/*========================== begin_copyright_notice ============================
+
+Copyright (C) 2023 Intel Corporation
+
+SPDX-License-Identifier: MIT
+
+============================= end_copyright_notice ===========================*/
+
+/*========================== begin_copyright_notice ============================
+
+Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+See https://llvm.org/LICENSE.txt for license information.
+SPDX-License-Identifier: Apache-2.0 with LLVM-exception
+
+============================= end_copyright_notice ===========================*/
+
+# Description:
+# Disable the option to avoid shortening of llvm.memset, which isn't supported
+# by our memset lowering / LowerGEPForPrivMem pass, and leads to suboptimal CG.
+#
+# Shortening sequence to avoid:
+# call void @llvm.memset.p0i8.i64(i8* %ptr, i8 0, i64 64, i1 false)
+# ->
+# %gep = getelementptr inbounds i8, i8* %ptr, i64 40
+# call void @llvm.memset.p0i8.i64(i8* %gep, i8 0, i64 24, i1 false)
+#
+# TODO: Improve memset handling / GEP to extract/insertelement lowering, then
+# abandon this patch.
+
+diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+index c5c8e880e..e620493d8 100644
+--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
++++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+@@ -113,7 +113,7 @@ DEBUG_COUNTER(MemorySSACounter, "dse-memoryssa",
+
+ static cl::opt<bool>
+ EnablePartialOverwriteTracking("enable-dse-partial-overwrite-tracking",
+-  cl::init(true), cl::Hidden,
++  cl::init(false), cl::Hidden,
+   cl::desc("Enable partial-overwrite tracking in DSE"));
+
+ static cl::opt<bool>
+