[Clang][Fortify] drop inline decls when redeclared

When an inline builtin declaration is shadowed by an actual declaration, we must
reference the actual declaration, even if it's not the last, following GCC
behavior.

This fixes #54715

Differential Revision: https://reviews.llvm.org/D123308

(cherry picked from commit 301e0d9)

Author: serge-sans-paille

clang/lib/CodeGen/CGExpr.cpp

@@ -4895,15 +4895,25 @@ RValue CodeGenFunction::EmitSimpleCallExpr(const CallExpr *E,
   return EmitCall(E->getCallee()->getType(), Callee, E, ReturnValue);
 }
 
+// Detect the unusual situation where an inline version is shadowed by a
+// non-inline version. In that case we should pick the external one
+// everywhere. That's GCC behavior too.
+static bool OnlyHasInlineBuiltinDeclaration(const FunctionDecl *FD) {
+  for (const FunctionDecl *PD = FD; PD; PD = PD->getPreviousDecl())
+    if (!PD->isInlineBuiltinDeclaration())
+      return false;
+  return true;
+}
+
 static CGCallee EmitDirectCallee(CodeGenFunction &CGF, GlobalDecl GD) {
   const FunctionDecl *FD = cast<FunctionDecl>(GD.getDecl());
 
   if (auto builtinID = FD->getBuiltinID()) {
     std::string FDInlineName = (FD->getName() + ".inline").str();
     // When directing calling an inline builtin, call it through it's mangled
     // name to make it clear it's not the actual builtin.
-    if (FD->isInlineBuiltinDeclaration() &&
-        CGF.CurFn->getName() != FDInlineName) {
+    if (CGF.CurFn->getName() != FDInlineName &&
+        OnlyHasInlineBuiltinDeclaration(FD)) {
       llvm::Constant *CalleePtr = EmitFunctionDeclPointer(CGF.CGM, GD);
       llvm::Function *Fn = llvm::cast<llvm::Function>(CalleePtr);
       llvm::Module *M = Fn->getParent();

clang/test/CodeGen/fread-inline-builtin-late-redecl.c

@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -triple x86_64 -S -emit-llvm -disable-llvm-passes -o - %s | FileCheck %s
+//
+// Verifies that clang-generated *.inline are removed when shadowed by an
+// external definition, even when that definition appears at the end of the
+// file.
+
+// CHECK-NOT: strlen.inline
+
+extern unsigned long strlen(char const *s);
+
+extern __inline __attribute__((__always_inline__)) __attribute__((__gnu_inline__)) unsigned long strlen(char const *s) {
+  return 1;
+}
+
+static unsigned long chesterfield(char const *s) {
+  return strlen(s);
+}
+static unsigned long (*_strlen)(char const *ptr);
+
+unsigned long blutch(char const *s) {
+  return chesterfield(s);
+}
+
+unsigned long strlen(char const *s) {
+  return _strlen(s);
+}