Index: cfe/trunk/include/clang/AST/Decl.h
===================================================================
--- cfe/trunk/include/clang/AST/Decl.h
+++ cfe/trunk/include/clang/AST/Decl.h
@@ -1632,6 +1632,11 @@
   /// skipped.
   unsigned HasSkippedBody : 1;
 
+  /// Indicates if the function declaration will have a body, once we're done
+  /// parsing it.  (We don't set it to false when we're done parsing, in the
+  /// hopes this is simpler.)
+  unsigned WillHaveBody : 1;
+
   /// \brief End part of this FunctionDecl's source range.
   ///
   /// We could compute the full range in getSourceRange(). However, when we're
@@ -1701,25 +1706,21 @@
 
 protected:
   FunctionDecl(Kind DK, ASTContext &C, DeclContext *DC, SourceLocation StartLoc,
-               const DeclarationNameInfo &NameInfo,
-               QualType T, TypeSourceInfo *TInfo,
-               StorageClass S, bool isInlineSpecified,
+               const DeclarationNameInfo &NameInfo, QualType T,
+               TypeSourceInfo *TInfo, StorageClass S, bool isInlineSpecified,
                bool isConstexprSpecified)
-    : DeclaratorDecl(DK, DC, NameInfo.getLoc(), NameInfo.getName(), T, TInfo,
-                     StartLoc),
-      DeclContext(DK),
-      redeclarable_base(C),
-      ParamInfo(nullptr), Body(),
-      SClass(S),
-      IsInline(isInlineSpecified), IsInlineSpecified(isInlineSpecified),
-      IsVirtualAsWritten(false), IsPure(false), HasInheritedPrototype(false),
-      HasWrittenPrototype(true), IsDeleted(false), IsTrivial(false),
-      IsDefaulted(false), IsExplicitlyDefaulted(false),
-      HasImplicitReturnZero(false), IsLateTemplateParsed(false),
-      IsConstexpr(isConstexprSpecified), UsesSEHTry(false),
-      HasSkippedBody(false), EndRangeLoc(NameInfo.getEndLoc()),
-      TemplateOrSpecialization(),
-      DNLoc(NameInfo.getInfo()) {}
+      : DeclaratorDecl(DK, DC, NameInfo.getLoc(), NameInfo.getName(), T, TInfo,
+                       StartLoc),
+        DeclContext(DK), redeclarable_base(C), ParamInfo(nullptr), Body(),
+        SClass(S), IsInline(isInlineSpecified),
+        IsInlineSpecified(isInlineSpecified), IsVirtualAsWritten(false),
+        IsPure(false), HasInheritedPrototype(false), HasWrittenPrototype(true),
+        IsDeleted(false), IsTrivial(false), IsDefaulted(false),
+        IsExplicitlyDefaulted(false), HasImplicitReturnZero(false),
+        IsLateTemplateParsed(false), IsConstexpr(isConstexprSpecified),
+        UsesSEHTry(false), HasSkippedBody(false), WillHaveBody(false),
+        EndRangeLoc(NameInfo.getEndLoc()), TemplateOrSpecialization(),
+        DNLoc(NameInfo.getInfo()) {}
 
   typedef Redeclarable<FunctionDecl> redeclarable_base;
   FunctionDecl *getNextRedeclarationImpl() override {
@@ -2001,6 +2002,10 @@
   bool hasSkippedBody() const { return HasSkippedBody; }
   void setHasSkippedBody(bool Skipped = true) { HasSkippedBody = Skipped; }
 
+  /// True if this function will eventually have a body, once it's fully parsed.
+  bool willHaveBody() const { return WillHaveBody; }
+  void setWillHaveBody(bool V = true) { WillHaveBody = V; }
+
   void setPreviousDeclaration(FunctionDecl * PrevDecl);
 
   FunctionDecl *getCanonicalDecl() override;
Index: cfe/trunk/lib/AST/Decl.cpp
===================================================================
--- cfe/trunk/lib/AST/Decl.cpp
+++ cfe/trunk/lib/AST/Decl.cpp
@@ -2933,7 +2933,7 @@
 /// of redeclarations of the given functions causes
 /// isInlineDefinitionExternallyVisible to change from false to true.
 bool FunctionDecl::doesDeclarationForceExternallyVisibleDefinition() const {
-  assert(!doesThisDeclarationHaveABody() &&
+  assert(!doesThisDeclarationHaveABody() && !willHaveBody() &&
          "Must have a declaration without a body.");
 
   ASTContext &Context = getASTContext();
@@ -3048,7 +3048,8 @@
 /// an externally visible symbol, but "extern inline" will not create an 
 /// externally visible symbol.
 bool FunctionDecl::isInlineDefinitionExternallyVisible() const {
-  assert(doesThisDeclarationHaveABody() && "Must have the function definition");
+  assert(doesThisDeclarationHaveABody() ||
+         willHaveBody() && "Must be a function definition");
   assert(isInlined() && "Function must be inline");
   ASTContext &Context = getASTContext();
   
Index: cfe/trunk/lib/Sema/SemaDecl.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaDecl.cpp
+++ cfe/trunk/lib/Sema/SemaDecl.cpp
@@ -5762,23 +5762,7 @@
     return false;
 
   // Okay, go ahead and call the relatively-more-expensive function.
-
-#ifndef NDEBUG
-  // AST quite reasonably asserts that it's working on a function
-  // definition.  We don't really have a way to tell it that we're
-  // currently defining the function, so just lie to it in +Asserts
-  // builds.  This is an awful hack.
-  FD->setLazyBody(1);
-#endif
-
-  bool isC99Inline =
-      S.Context.GetGVALinkageForFunction(FD) == GVA_AvailableExternally;
-
-#ifndef NDEBUG
-  FD->setLazyBody(0);
-#endif
-
-  return isC99Inline;
+  return S.Context.GetGVALinkageForFunction(FD) == GVA_AvailableExternally;
 }
 
 /// Determine whether a variable is extern "C" prior to attaching
@@ -11487,6 +11471,11 @@
       return D;
   }
 
+  // Mark this function as "will have a body eventually".  This lets users to
+  // call e.g. isInlineDefinitionExternallyVisible while we're still parsing
+  // this function.
+  FD->setWillHaveBody();
+
   // If we are instantiating a generic lambda call operator, push
   // a LambdaScopeInfo onto the function stack.  But use the information
   // that's already been calculated (ActOnLambdaExpr) to prime the current
Index: cfe/trunk/test/SemaCUDA/gnu-inline.cu
===================================================================
--- cfe/trunk/test/SemaCUDA/gnu-inline.cu
+++ cfe/trunk/test/SemaCUDA/gnu-inline.cu
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+#include "Inputs/cuda.h"
+
+// expected-no-diagnostics
+
+// Check that we can handle gnu_inline functions when compiling in CUDA mode.
+
+void foo();
+inline __attribute__((gnu_inline)) void bar() { foo(); }