[llvm-branch-commits] [libc] release/19.x: [libc] Only add '-fno-builtin-*' on the entrypoints that use them (#100481) (PR #100496)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport 8e43acbfedf53ded43ec693ddaaf518cb7416c1c

Requested by: @<!-- -->jhuber6

---
Full diff: https://github.com/llvm/llvm-project/pull/100496.diff


2 Files Affected:

- (modified) libc/cmake/modules/LLVMLibCCompileOptionRules.cmake (+1-10) 
- (modified) libc/cmake/modules/LLVMLibCObjectRules.cmake (+11) 


``````````diff
diff --git a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
index 97d1c7262d24d..7a1c45a814eb6 100644
--- a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
+++ b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
@@ -104,16 +104,7 @@ 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

``````````

</details>


https://github.com/llvm/llvm-project/pull/100496