From f3f8d2a52ebc0acbe6269a0302f90c21668e2404 Mon Sep 17 00:00:00 2001
From: Charles Davis <cdavis@mines.edu>
Date: Thu, 18 Feb 2010 02:00:42 +0000
Subject: [PATCH] Allow redefinitions of extern inline functions in GNU89 mode,
 just as GCC does. Fixes PR5253.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@96553 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaDecl.cpp        | 20 ++++++++++++++++++--
 test/CodeGen/extern-inline.c | 25 +++++++++++++++++++++++++
 test/Sema/inline.c           | 18 +++++++++++++++++-
 3 files changed, 60 insertions(+), 3 deletions(-)
 create mode 100644 test/CodeGen/extern-inline.c

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index e7217dc220..949669aa57 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -908,6 +908,16 @@ static Sema::CXXSpecialMember getSpecialMember(ASTContext &Ctx,
   return Sema::CXXCopyAssignment;
 }
 
+/// canREdefineFunction - checks if a function can be redefined. Currently,
+/// only extern inline functions can be redefined, and even then only in
+/// GNU89 mode.
+static bool canRedefineFunction(const FunctionDecl *FD,
+                                const LangOptions& LangOpts) {
+  return (LangOpts.GNUMode && !LangOpts.C99 && !LangOpts.CPlusPlus &&
+          FD->isInlineSpecified() &&
+          FD->getStorageClass() == FunctionDecl::Extern);
+}
+
 /// MergeFunctionDecl - We just parsed a function 'New' from
 /// declarator D which has the same name and scope as a previous
 /// declaration 'Old'.  Figure out how to resolve this situation,
@@ -956,9 +966,12 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD) {
   QualType OldQType = Context.getCanonicalType(Old->getType());
   QualType NewQType = Context.getCanonicalType(New->getType());
 
+  // Don't complain about this if we're in GNU89 mode and the old function
+  // is an extern inline function.
   if (!isa<CXXMethodDecl>(New) && !isa<CXXMethodDecl>(Old) &&
       New->getStorageClass() == FunctionDecl::Static &&
-      Old->getStorageClass() != FunctionDecl::Static) {
+      Old->getStorageClass() != FunctionDecl::Static &&
+      !canRedefineFunction(Old, getLangOptions())) {
     Diag(New->getLocation(), diag::err_static_non_static)
       << New;
     Diag(Old->getLocation(), PrevDiag);
@@ -4062,8 +4075,11 @@ Sema::DeclPtrTy Sema::ActOnStartOfFunctionDef(Scope *FnBodyScope, DeclPtrTy D) {
   CurFunctionNeedsScopeChecking = false;
 
   // See if this is a redefinition.
+  // But don't complain if we're in GNU89 mode and the previous definition
+  // was an extern inline function.
   const FunctionDecl *Definition;
-  if (FD->getBody(Definition)) {
+  if (FD->getBody(Definition) &&
+      !canRedefineFunction(Definition, getLangOptions())) {
     Diag(FD->getLocation(), diag::err_redefinition) << FD->getDeclName();
     Diag(Definition->getLocation(), diag::note_previous_definition);
   }
diff --git a/test/CodeGen/extern-inline.c b/test/CodeGen/extern-inline.c
new file mode 100644
index 0000000000..5dd9bfda57
--- /dev/null
+++ b/test/CodeGen/extern-inline.c
@@ -0,0 +1,25 @@
+// RUN: %clang -S -emit-llvm -std=gnu89 -o - %s | FileCheck %s
+// PR5253
+
+// If an extern inline function is redefined, functions should call the
+// redefinition.
+extern inline int f(int a) {return a;}
+int g(void) {return f(0);}
+// CHECK: call i32 @f
+int f(int b) {return 1+b;}
+// CHECK: load i32* %{{.*}}
+// CHECK: add nsw i32 1, %{{.*}}
+int h(void) {return f(1);}
+// CHECK: call i32 @f
+
+// It shouldn't matter if the function was redefined static.
+extern inline int f2(int a, int b) {return a+b;}
+int g2(void) {return f2(0,1);}
+// CHECK: call i32 @f2
+static int f2(int a, int b) {return a*b;}
+// CHECK: load i32* %{{.*}}
+// CHECK: load i32* %{{.*}}
+// CHECK: mul i32 %{{.*}}, %{{.*}}
+int h2(void) {return f2(1,2);}
+// CHECK: call i32 @f2
+
diff --git a/test/Sema/inline.c b/test/Sema/inline.c
index 3c99f24337..b4795d3d93 100644
--- a/test/Sema/inline.c
+++ b/test/Sema/inline.c
@@ -1,6 +1,22 @@
-// RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=gnu89 -fsyntax-only -verify %s
 
 // Check that we don't allow illegal uses of inline
 inline int a; // expected-error{{'inline' can only appear on functions}}
 typedef inline int b; // expected-error{{'inline' can only appear on functions}}
 int d(inline int a); // expected-error{{'inline' can only appear on functions}}
+
+// PR5253
+// GNU Extension: check that we can redefine an extern inline function
+extern inline int f(int a) {return a;}
+int f(int b) {return b;} // expected-note{{previous definition is here}}
+// And now check that we can't redefine a normal function
+int f(int c) {return c;} // expected-error{{redefinition of 'f'}}
+
+// Check that we can redefine an extern inline function as a static function
+extern inline int g(int a) {return a;}
+static int g(int b) {return b;}
+
+// Check that we ensure the types of the two definitions are the same
+extern inline int h(int a) {return a;} // expected-note{{previous definition is here}}
+int h(short b) {return b;}  // expected-error{{conflicting types for 'h'}}
+
-- 
2.40.0