[libc-commits] [libc] [libc] Only add '-fno-builtin-*' on the entrypoints that use them (PR #100481)

[Joseph Huber via libc-commits]

https://github.com/jhuber6 created https://github.com/llvm/llvm-project/pull/100481

Summary:
The GPU build needs to be able to inline stuff in LTO. Builtin
transformations cause problems on the functions that the optimizer does
heavy libcall recognition on. Previously we moved to using
`-fno-builtin-*` to allow us to only disable the problematic ones.
However, this still didn't allow inlining because each function had the
attribute that told the inliner not to inlining a nobuiltin function
into a non-nobuiltin function

This patch fixes that by only applying these attributes to the
entrypoints that define them. That is enough to prevent recursive calls
within the definitoins themselves.


>From 627ce42f70d280bdce5188cccb7159d15fa8c113 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Wed, 24 Jul 2024 17:36:59 -0500
Subject: [PATCH] [libc] Only add '-fno-builtin-*' on the entrypoints that use
 them

Summary:
The GPU build needs to be able to inline stuff in LTO. Builtin
transformations cause problems on the functions that the optimizer does
heavy libcall recognition on. Previously we moved to using
`-fno-builtin-*` to allow us to only disable the problematic ones.
However, this still didn't allow inlining because each function had the
attribute that told the inliner not to inlining a nobuiltin function
into a non-nobuiltin function

This patch fixes that by only applying these attributes to the
entrypoints that define them. That is enough to prevent recursive calls
within the definitoins themselves.
---
 libc/cmake/modules/LLVMLibCCompileOptionRules.cmake | 11 +----------
 libc/cmake/modules/LLVMLibCObjectRules.cmake        | 11 +++++++++++
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
index 0f1ef6a575277..9fc10375a1d37 100644
--- a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
+++ b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
@@ -115,16 +115,7 @@ function(_get_common_compile_options output_var flags)
       list(APPEND compile_options "-ffixed-point")
     endif()
 
-    # Builtin recognition causes issues when trying to implement the builtin
-    # functions themselves. The GPU backends do not use libcalls so we disable
-    # the known problematic ones. This allows inlining during LTO linking.
-    if(LIBC_TARGET_OS_IS_GPU)
-      set(libc_builtins bcmp strlen memmem bzero memcmp memcpy memmem memmove
-                        memset strcmp strstr)
-      foreach(builtin ${libc_builtins})
-        list(APPEND compile_options "-fno-builtin-${builtin}")
-      endforeach()
-    else()
+    if(NOT LIBC_TARGET_OS_IS_GPU)
       list(APPEND compile_options "-fno-builtin")
     endif()
 
diff --git a/libc/cmake/modules/LLVMLibCObjectRules.cmake b/libc/cmake/modules/LLVMLibCObjectRules.cmake
index 2d3db38ecd8a3..68b5ed1ed51c0 100644
--- a/libc/cmake/modules/LLVMLibCObjectRules.cmake
+++ b/libc/cmake/modules/LLVMLibCObjectRules.cmake
@@ -279,6 +279,17 @@ function(create_entrypoint_object fq_target_name)
   add_dependencies(${fq_target_name} ${full_deps_list})
   target_link_libraries(${fq_target_name} ${full_deps_list})
 
+  # Builtin recognition causes issues when trying to implement the builtin
+  # functions themselves. The GPU backends do not use libcalls so we disable the
+  # known problematic ones on the entrypoints that implement them.
+  if(LIBC_TARGET_OS_IS_GPU)
+    set(libc_builtins bcmp strlen memmem bzero memcmp memcpy memmem memmove
+                      memset strcmp strstr)
+    if(${ADD_ENTRYPOINT_OBJ_NAME} IN_LIST libc_builtins)
+      target_compile_options(${fq_target_name} PRIVATE -fno-builtin-${ADD_ENTRYPOINT_OBJ_NAME})
+    endif()
+  endif()
+
   set_target_properties(
     ${fq_target_name}
     PROPERTIES