From 03fe02e7493f4de8fc5698db151391bbd5b358f4 Mon Sep 17 00:00:00 2001
From: George Burgess IV <george.burgess.iv@gmail.com>
Date: Thu, 16 Apr 2020 10:56:19 -0700
Subject: [PATCH] [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 505dbc084790c03f7793d371faa24d79ff550c3d)
---
 clang/lib/CodeGen/CodeGenModule.cpp              | 12 +++++++++---
 .../memcpy-no-nobuiltin-if-not-emitted.cpp       | 16 ++++++++++++++++
 2 files changed, 25 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/CodeGen/memcpy-no-nobuiltin-if-not-emitted.cpp

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 73c41dc4cf3f..a735bdd814ed 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1848,9 +1848,15 @@ void CodeGenModule::SetFunctionAttributes(GlobalDecl GD, llvm::Function *F,
      F->setSection(SA->getName());
 
   // If we plan on emitting this inline builtin, we can't treat it as a builtin.
-  if (FD->isInlineBuiltinDeclaration() && shouldEmitFunction(FD)) {
-    F->addAttribute(llvm::AttributeList::FunctionIndex,
-                    llvm::Attribute::NoBuiltin);
+  if (FD->isInlineBuiltinDeclaration()) {
+    const FunctionDecl *FDBody;
+    bool HasBody = FD->hasBody(FDBody);
+    (void)HasBody;
+    assert(HasBody && "Inline builtin declarations should always have an "
+                      "available body!");
+    if (shouldEmitFunction(FDBody))
+      F->addAttribute(llvm::AttributeList::FunctionIndex,
+                      llvm::Attribute::NoBuiltin);
   }
 
   if (FD->isReplaceableGlobalAllocationFunction()) {
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 000000000000..d27aa9c53413
--- /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