1; RUN: opt < %s -passes=globaldce -S | FileCheck %s 2 3target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" 4 5declare dso_local noalias nonnull ptr @_Znwm(i64) 6declare { ptr, i1 } @llvm.type.checked.load(ptr, i32, metadata) 7 8; %struct.A is a C++ struct with two virtual functions, A::foo and A::bar. The 9; !vcall_visibility metadata is set on the vtable, so we know that all virtual 10; calls through this vtable are visible and use the @llvm.type.checked.load 11; intrinsic. Function test_A makes a call to A::foo, but there is no call to 12; A::bar anywhere, so A::bar can be deleted, and its vtable slot replaced with 13; null. 14 15%struct.A = type { ptr } 16 17; The pointer to A::bar in the vtable can be removed, because it will never be 18; loaded. We replace it with null to keep the layout the same. Because it is at 19; the end of the vtable we could potentially shrink the vtable, but don't 20; currently do that. 21; CHECK: @_ZTV1A = internal unnamed_addr constant { [4 x ptr] } { [4 x ptr] [ptr null, ptr null, ptr @_ZN1A3fooEv, ptr null] } 22@_ZTV1A = internal unnamed_addr constant { [4 x ptr] } { [4 x ptr] [ptr null, ptr null, ptr @_ZN1A3fooEv, ptr @_ZN1A3barEv] }, align 8, !type !0, !type !1, !type !2, !vcall_visibility !3 23 24; A::foo is called, so must be retained. 25; CHECK: define internal i32 @_ZN1A3fooEv( 26define internal i32 @_ZN1A3fooEv(ptr nocapture readnone %this) { 27entry: 28 ret i32 42 29} 30 31; A::bar is not used, so can be deleted. 32; CHECK-NOT: define internal i32 @_ZN1A3barEv( 33define internal i32 @_ZN1A3barEv(ptr nocapture readnone %this) { 34entry: 35 ret i32 1337 36} 37 38define dso_local i32 @test_A() { 39entry: 40 %call = tail call ptr @_Znwm(i64 8) 41 store ptr getelementptr inbounds inrange(-16, 16) ({ [4 x ptr] }, ptr @_ZTV1A, i64 0, i32 0, i64 2), ptr %call, align 8 42 %0 = tail call { ptr, i1 } @llvm.type.checked.load(ptr getelementptr inbounds inrange(-16, 16) ({ [4 x ptr] }, ptr @_ZTV1A, i64 0, i32 0, i64 2), i32 0, metadata !"_ZTS1A"), !nosanitize !9 43 %1 = extractvalue { ptr, i1 } %0, 0, !nosanitize !9 44 %call1 = tail call i32 %1(ptr nonnull %call) 45 ret i32 %call1 46} 47 48!llvm.module.flags = !{!4} 49 50!0 = !{i64 16, !"_ZTS1A"} 51!1 = !{i64 16, !"_ZTSM1AFivE.virtual"} 52!2 = !{i64 24, !"_ZTSM1AFivE.virtual"} 53!3 = !{i64 2} 54!4 = !{i32 1, !"Virtual Function Elim", i32 1} 55!9 = !{} 56