Simplify handling of builtin with inline redefinition

It is a common practice in glibc header to provide an inline redefinition of an
existing function. It is especially the case for fortified function.

Clang currently has an imperfect approach to the problem, using a combination of
trivially recursive function detection and noinline attribute.

Simplify the logic by suffixing these functions by `.inline` during codegen, so
that they are not recognized as builtin by llvm.

After that patch, clang passes all tests from https://github.com/serge-sans-paille/fortify-test-suite

Differential Revision: https://reviews.llvm.org/D109967

Author: serge-sans-paille

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -1301,6 +1301,11 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
   FunctionArgList Args;
   QualType ResTy = BuildFunctionArgList(GD, Args);
 
+  // Give a different name to inline builtin to avoid conflict with actual
+  // builtins.
+  if (FD->isInlineBuiltinDeclaration() && Fn)
+    Fn->setName(Fn->getName() + ".inline");
+
   // Check if we should generate debug info for this function.
   if (FD->hasAttr<NoDebugAttr>()) {
     // Clear non-distinct debug info that was possibly attached to the function

clang/lib/CodeGen/CodeGenModule.cpp

@@ -3169,6 +3169,11 @@ bool CodeGenModule::shouldEmitFunction(GlobalDecl GD) {
     }
   }
 
+  // Inline builtins declaration must be emitted. They often are fortified
+  // functions.
+  if (F->isInlineBuiltinDeclaration())
+    return true;
+
   // PR9614. Avoid cases where the source code is lying to us. An available
   // externally function should have an equivalent function somewhere else,
   // but a function that calls itself through asm label/`__builtin_` trickery is

clang/test/CodeGen/memcpy-inline-builtin.c

@@ -0,0 +1,44 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
+
+// RUN: %clang_cc1 -triple x86_64 -S -emit-llvm -o - %s | FileCheck %s
+//
+// Verifies that clang detects memcpy inline version and uses it instead of the builtin.
+
+typedef unsigned long size_t;
+
+// Clang requires these attributes for a function to be redefined.
+#define AVAILABLE_EXTERNALLY extern inline __attribute__((always_inline)) __attribute__((gnu_inline))
+
+// Clang recognizes an inline builtin and renames it to prevent conflict with builtins.
+AVAILABLE_EXTERNALLY void *memcpy(void *a, const void *b, size_t c) {
+  asm("# memcpy.inline marker");
+  return __builtin_memcpy(a, b, c);
+}
+
+// CHECK-LABEL: @foo(
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[A_ADDR_I:%.*]] = alloca i8*, align 8
+// CHECK-NEXT:    [[B_ADDR_I:%.*]] = alloca i8*, align 8
+// CHECK-NEXT:    [[C_ADDR_I:%.*]] = alloca i64, align 8
+// CHECK-NEXT:    [[A_ADDR:%.*]] = alloca i8*, align 8
+// CHECK-NEXT:    [[B_ADDR:%.*]] = alloca i8*, align 8
+// CHECK-NEXT:    [[C_ADDR:%.*]] = alloca i64, align 8
+// CHECK-NEXT:    store i8* [[A:%.*]], i8** [[A_ADDR]], align 8
+// CHECK-NEXT:    store i8* [[B:%.*]], i8** [[B_ADDR]], align 8
+// CHECK-NEXT:    store i64 [[C:%.*]], i64* [[C_ADDR]], align 8
+// CHECK-NEXT:    [[TMP0:%.*]] = load i8*, i8** [[A_ADDR]], align 8
+// CHECK-NEXT:    [[TMP1:%.*]] = load i8*, i8** [[B_ADDR]], align 8
+// CHECK-NEXT:    [[TMP2:%.*]] = load i64, i64* [[C_ADDR]], align 8
+// CHECK-NEXT:    store i8* [[TMP0]], i8** [[A_ADDR_I]], align 8
+// CHECK-NEXT:    store i8* [[TMP1]], i8** [[B_ADDR_I]], align 8
+// CHECK-NEXT:    store i64 [[TMP2]], i64* [[C_ADDR_I]], align 8
+// CHECK-NEXT:    call void asm sideeffect "# memcpy.inline marker", "~{dirflag},~{fpsr},~{flags}"() #[[ATTR2:[0-9]+]], !srcloc !2
+// CHECK-NEXT:    [[TMP3:%.*]] = load i8*, i8** [[A_ADDR_I]], align 8
+// CHECK-NEXT:    [[TMP4:%.*]] = load i8*, i8** [[B_ADDR_I]], align 8
+// CHECK-NEXT:    [[TMP5:%.*]] = load i64, i64* [[C_ADDR_I]], align 8
+// CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 1 [[TMP3]], i8* align 1 [[TMP4]], i64 [[TMP5]], i1 false) #[[ATTR2]]
+// CHECK-NEXT:    ret void
+//
+void foo(void *a, const void *b, size_t c) {
+  memcpy(a, b, c);
+}

clang/test/CodeGen/memcpy-no-nobuiltin-if-not-emitted.c

@@ -4,7 +4,8 @@
 //
 // CHECK-WITH-DECL-NOT: @llvm.memcpy
 // CHECK-NO-DECL: @llvm.memcpy
-// CHECK-SELF-REF-DECL: @llvm.memcpy
+// CHECK-SELF-REF-DECL-LABEL: define dso_local i8* @memcpy.inline
+// CHECK-SELF-REF-DECL:       @memcpy(
 //
 #include <memcpy-nobuiltin.inc>
 void test(void *dest, void const *from, size_t n) {

clang/test/CodeGen/memcpy-nobuiltin.c

@@ -32,14 +32,14 @@ void f(void) {
 
 // CHECK-LABEL: define{{.*}} void @f()
 // CHECK: call void @foo()
-// CHECK: call i32 @abs(i32 0)
+// CHECK: call i32 @abs(i32 %0)
 // CHECK: call i8* @strrchr(
 // CHECK: call void @llvm.prefetch.p0i8(
 // CHECK: call i8* @memchr(
 // CHECK: ret void
 
 // CHECK: declare void @foo()
-// CHECK: declare i32 @abs(i32
 // CHECK: declare i8* @strrchr(i8*, i32)
 // CHECK: declare i8* @memchr(
+// CHECK: declare i32 @abs(i32
 // CHECK: declare void @llvm.prefetch.p0i8(