[compiler-rt] [ARM][Compiler-RT] Add optional exclusion of libc provided ARM AEABI builtins from compiler-rt. (PR #137952)

[Simi Pallipurath via llvm-commits]

https://github.com/simpal01 updated https://github.com/llvm/llvm-project/pull/137952

>From 72ce8a9fb72f424372629d73a4fbef91a91e6acc Mon Sep 17 00:00:00 2001
From: Simi Pallipurath <simi.pallipurath at arm.com>
Date: Wed, 30 Apr 2025 11:25:10 +0100
Subject: [PATCH] [ARM][Compiler-RT] Add optional exclusion of libc provided
 ARM AEABI builtins from compiler-rt.

This patch introduces a new optional CMake flag:
  COMPILER_RT_EXCLUDE_LIBC_PROVIDED_ARM_AEABI_BUILTINS

When enabled, this flag excludes the following ARM AEABI
memory function implementations from the compiler-rt build:
	__aeabi_memset
	__aeabi_memcpy
	__aeabi_memmove

These functions are already provided by standard C
libraries like glibc, newlib, and picolibc, so excluding
them avoids duplicate symbol definitions and reduces
unnecessary code duplication.

Note: __aeabi_memcmp and other AEABI functions are not
excluded, as they are not defined in all standard libraries.

This change is useful for environments where libc provides
runtime routines, supporting more minimal, conflict free builds.
---
 compiler-rt/lib/builtins/CMakeLists.txt | 61 +++++++++++++++++--------
 1 file changed, 42 insertions(+), 19 deletions(-)

diff --git a/compiler-rt/lib/builtins/CMakeLists.txt b/compiler-rt/lib/builtins/CMakeLists.txt
index 0c986f484bf5e..cca41c431dbb1 100644
--- a/compiler-rt/lib/builtins/CMakeLists.txt
+++ b/compiler-rt/lib/builtins/CMakeLists.txt
@@ -230,6 +230,9 @@ set(GENERIC_TF_SOURCES
 option(COMPILER_RT_EXCLUDE_ATOMIC_BUILTIN
   "Skip the atomic builtin (these should normally be provided by a shared library)"
   On)
+option(COMPILER_RT_EXCLUDE_LIBC_PROVIDED_ARM_AEABI_BUILTINS
+  "Skip the standard C library provided arm aeabi builtins from compiler-rt)"
+  Off)
 
 if(NOT FUCHSIA AND NOT COMPILER_RT_BAREMETAL_BUILD AND NOT COMPILER_RT_GPU_BUILD)
   set(GENERIC_SOURCES
@@ -450,25 +453,45 @@ set(thumb1_base_SOURCES
   ${GENERIC_SOURCES}
 )
 
-set(arm_EABI_SOURCES
-  arm/aeabi_cdcmp.S
-  arm/aeabi_cdcmpeq_check_nan.c
-  arm/aeabi_cfcmp.S
-  arm/aeabi_cfcmpeq_check_nan.c
-  arm/aeabi_dcmp.S
-  arm/aeabi_div0.c
-  arm/aeabi_drsub.c
-  arm/aeabi_fcmp.S
-  arm/aeabi_frsub.c
-  arm/aeabi_idivmod.S
-  arm/aeabi_ldivmod.S
-  arm/aeabi_memcmp.S
-  arm/aeabi_memcpy.S
-  arm/aeabi_memmove.S
-  arm/aeabi_memset.S
-  arm/aeabi_uidivmod.S
-  arm/aeabi_uldivmod.S
-)
+if(NOT COMPILER_RT_EXCLUDE_LIBC_PROVIDED_ARM_AEABI_BUILTINS)
+  set(arm_EABI_SOURCES
+     arm/aeabi_cdcmp.S
+     arm/aeabi_cdcmpeq_check_nan.c
+     arm/aeabi_cfcmp.S
+     arm/aeabi_cfcmpeq_check_nan.c
+     arm/aeabi_dcmp.S
+     arm/aeabi_div0.c
+     arm/aeabi_drsub.c
+     arm/aeabi_fcmp.S
+     arm/aeabi_frsub.c
+     arm/aeabi_idivmod.S
+     arm/aeabi_ldivmod.S
+     arm/aeabi_memcmp.S
+     arm/aeabi_memcpy.S
+     arm/aeabi_memmove.S
+     arm/aeabi_memset.S
+     arm/aeabi_uidivmod.S
+     arm/aeabi_uldivmod.S
+  )
+else()
+	message(STATUS "COMPILER_RT_EXCLUDE_LIBC_PROVIDED_ARM_AEABI_BUILTINS is ON, so skipping __aeabi_memcpy, __aeabi_memmove and __aeabi_memset Sources")
+  set(arm_EABI_SOURCES
+     arm/aeabi_cdcmp.S
+     arm/aeabi_cdcmpeq_check_nan.c
+     arm/aeabi_cfcmp.S
+     arm/aeabi_cfcmpeq_check_nan.c
+     arm/aeabi_dcmp.S
+     arm/aeabi_div0.c
+     arm/aeabi_drsub.c
+     arm/aeabi_fcmp.S
+     arm/aeabi_frsub.c
+     arm/aeabi_idivmod.S
+     arm/aeabi_ldivmod.S
+     arm/aeabi_memcmp.S
+     arm/aeabi_uidivmod.S
+     arm/aeabi_uldivmod.S
+  )
+endif()
 
 set(arm_Thumb1_JT_SOURCES
   arm/switch16.S