llvm/test/Transforms/GlobalDCE/virtual-functions.ll

; RUN: opt < %s -passes=globaldce -S | FileCheck %s

target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"

declare dso_local noalias nonnull i8* @_Znwm(i64)
declare { i8*, i1 } @llvm.type.checked.load(i8*, i32, metadata)

; %struct.A is a C++ struct with two virtual functions, A::foo and A::bar. The
; !vcall_visibility metadata is set on the vtable, so we know that all virtual
; calls through this vtable are visible and use the @llvm.type.checked.load
; intrinsic. Function test_A makes a call to A::foo, but there is no call to
; A::bar anywhere, so A::bar can be deleted, and its vtable slot replaced with
; null.

%struct.A = type { i32 (...)** }

; The pointer to A::bar in the vtable can be removed, because it will never be
; loaded. We replace it with null to keep the layout the same. Because it is at
; the end of the vtable we could potentially shrink the vtable, but don't
; currently do that.
; CHECK: @_ZTV1A = internal unnamed_addr constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* null, i8* bitcast (i32 (%struct.A*)* @_ZN1A3fooEv to i8*), i8* null] }
@_ZTV1A = internal unnamed_addr constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* null, i8* bitcast (i32 (%struct.A*)* @_ZN1A3fooEv to i8*), i8* bitcast (i32 (%struct.A*)* @_ZN1A3barEv to i8*)] }, align 8, !type !0, !type !1, !type !2, !vcall_visibility !3

; A::foo is called, so must be retained.
; CHECK: define internal i32 @_ZN1A3fooEv(
define internal i32 @_ZN1A3fooEv(%struct.A* nocapture readnone %this) {
entry:
  ret i32 42
}

; A::bar is not used, so can be deleted.
; CHECK-NOT: define internal i32 @_ZN1A3barEv(
define internal i32 @_ZN1A3barEv(%struct.A* nocapture readnone %this) {
entry:
  ret i32 1337
}

define dso_local i32 @test_A() {
entry:
  %call = tail call i8* @_Znwm(i64 8)
  %0 = bitcast i8* %call to %struct.A*
  %1 = bitcast i8* %call to i32 (...)***
  store i32 (...)** bitcast (i8** getelementptr inbounds ({ [4 x i8*] }, { [4 x i8*] }* @_ZTV1A, i64 0, inrange i32 0, i64 2) to i32 (...)**), i32 (...)*** %1, align 8
  %2 = tail call { i8*, i1 } @llvm.type.checked.load(i8* bitcast (i8** getelementptr inbounds ({ [4 x i8*] }, { [4 x i8*] }* @_ZTV1A, i64 0, inrange i32 0, i64 2) to i8*), i32 0, metadata !"_ZTS1A"), !nosanitize !9
  %3 = extractvalue { i8*, i1 } %2, 0, !nosanitize !9
  %4 = bitcast i8* %3 to i32 (%struct.A*)*, !nosanitize !9
  %call1 = tail call i32 %4(%struct.A* nonnull %0)
  ret i32 %call1
}

!llvm.module.flags = !{!4}

!0 = !{i64 16, !"_ZTS1A"}
!1 = !{i64 16, !"_ZTSM1AFivE.virtual"}
!2 = !{i64 24, !"_ZTSM1AFivE.virtual"}
!3 = !{i64 2}
!4 = !{i32 1, !"Virtual Function Elim", i32 1}
!9 = !{}