Author: spatel Date: Fri Jan 19 07:14:51 2018 New Revision: 322950 URL: http://llvm.org/viewvc/llvm-project?rev=322950&view=rev Log: [CodeGenCXX] annotate a GEP to a derived class with 'inbounds' (PR35909)
The standard says: [expr.static.cast] p11: "If the prvalue of type “pointer to cv1 B” points to a B that is actually a subobject of an object of type D, the resulting pointer points to the enclosing object of type D. Otherwise, the behavior is undefined." Therefore, the GEP must be inbounds. This should solve the failure to optimize away a null check shown in PR35909: https://bugs.llvm.org/show_bug.cgi?id=35909 Differential Revision: https://reviews.llvm.org/D42249 Added: cfe/trunk/test/CodeGenCXX/derived-cast.cpp Modified: cfe/trunk/lib/CodeGen/CGClass.cpp cfe/trunk/test/CodeGenCXX/catch-undef-behavior.cpp Modified: cfe/trunk/lib/CodeGen/CGClass.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGClass.cpp?rev=322950&r1=322949&r2=322950&view=diff ============================================================================== --- cfe/trunk/lib/CodeGen/CGClass.cpp (original) +++ cfe/trunk/lib/CodeGen/CGClass.cpp Fri Jan 19 07:14:51 2018 @@ -406,8 +406,8 @@ CodeGenFunction::GetAddressOfDerivedClas // Apply the offset. llvm::Value *Value = Builder.CreateBitCast(BaseAddr.getPointer(), Int8PtrTy); - Value = Builder.CreateGEP(Value, Builder.CreateNeg(NonVirtualOffset), - "sub.ptr"); + Value = Builder.CreateInBoundsGEP(Value, Builder.CreateNeg(NonVirtualOffset), + "sub.ptr"); // Just cast. Value = Builder.CreateBitCast(Value, DerivedPtrTy); Modified: cfe/trunk/test/CodeGenCXX/catch-undef-behavior.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/catch-undef-behavior.cpp?rev=322950&r1=322949&r2=322950&view=diff ============================================================================== --- cfe/trunk/test/CodeGenCXX/catch-undef-behavior.cpp (original) +++ cfe/trunk/test/CodeGenCXX/catch-undef-behavior.cpp Fri Jan 19 07:14:51 2018 @@ -371,7 +371,7 @@ class C : public A, public B // align=16 void downcast_pointer(B *b) { (void) static_cast<C*>(b); // Alignment check from EmitTypeCheck(TCK_DowncastPointer, ...) - // CHECK: [[SUB:%[.a-z0-9]*]] = getelementptr i8, i8* {{.*}}, i64 -16 + // CHECK: [[SUB:%[.a-z0-9]*]] = getelementptr inbounds i8, i8* {{.*}}, i64 -16 // CHECK-NEXT: [[C:%.+]] = bitcast i8* [[SUB]] to %class.C* // null check goes here // CHECK: [[FROM_PHI:%.+]] = phi %class.C* [ [[C]], {{.*}} ], {{.*}} @@ -388,7 +388,7 @@ void downcast_pointer(B *b) { void downcast_reference(B &b) { (void) static_cast<C&>(b); // Alignment check from EmitTypeCheck(TCK_DowncastReference, ...) - // CHECK: [[SUB:%[.a-z0-9]*]] = getelementptr i8, i8* {{.*}}, i64 -16 + // CHECK: [[SUB:%[.a-z0-9]*]] = getelementptr inbounds i8, i8* {{.*}}, i64 -16 // CHECK-NEXT: [[C:%.+]] = bitcast i8* [[SUB]] to %class.C* // Objectsize check goes here // CHECK: [[C_INT:%.+]] = ptrtoint %class.C* [[C]] to i64 Added: cfe/trunk/test/CodeGenCXX/derived-cast.cpp URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/derived-cast.cpp?rev=322950&view=auto ============================================================================== --- cfe/trunk/test/CodeGenCXX/derived-cast.cpp (added) +++ cfe/trunk/test/CodeGenCXX/derived-cast.cpp Fri Jan 19 07:14:51 2018 @@ -0,0 +1,27 @@ +// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s + +class A { + int a; +}; + +class B { + int b; +public: + A *getAsA(); +}; + +class X : public A, public B { + int x; +}; + +// PR35909 - https://bugs.llvm.org/show_bug.cgi?id=35909 + +A *B::getAsA() { + return static_cast<X*>(this); + + // CHECK-LABEL: define %class.A* @_ZN1B6getAsAEv + // CHECK: %[[THIS:.*]] = load %class.B*, %class.B** + // CHECK-NEXT: %[[BC:.*]] = bitcast %class.B* %[[THIS]] to i8* + // CHECK-NEXT: getelementptr inbounds i8, i8* %[[BC]], i64 -4 +} + _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
