[CodeGen] fix inline builtin-related breakage from D78162

In cases where we have multiple decls of an inline builtin, we may need
to go hunting for the one with a definition when setting function
attributes.

An additional test-case was provided on
https://github.com/ClangBuiltLinux/linux/issues/979

(cherry picked from commit 94908088a831141cfbdd15fc5837dccf30cfeeb6)

1 files changed, 16 insertions, 0 deletions

diff --git a/clang/test/CodeGen/memcpy-no-nobuiltin-if-not-emitted.cpp b/clang/test/CodeGen/memcpy-no-nobuiltin-if-not-emitted.cpp
new file mode 100644
index 00000000000..d27aa9c5341
--- /dev/null
+++ b/clang/test/CodeGen/memcpy-no-nobuiltin-if-not-emitted.cpp
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -triple i686-linux-gnu -std=c++11 -S -emit-llvm -o - %s | FileCheck %s
+//
+// Regression test for the issue reported at
+// https://reviews.llvm.org/D78162#1986104
+
+typedef unsigned long size_t;
+
+extern "C" __inline__ __attribute__((__gnu_inline__)) void *memcpy(void *a, const void *b, unsigned c) {
+  return __builtin_memcpy(a, b, c);
+}
+void *memcpy(void *, const void *, unsigned);
+
+// CHECK-LABEL: define void @_Z1av
+void a() { (void)memcpy; }
+
+// CHECK-NOT: nobuiltin