458676db6e
Summary: First patch to support Safe Whole Program Devirtualization Enablement, see RFC here: http://lists.llvm.org/pipermail/llvm-dev/2019-December/137543.html Always emit !vcall_visibility metadata under -fwhole-program-vtables, and not just for -fvirtual-function-elimination. The vcall visibility metadata will (in a subsequent patch) be used to communicate to WPD which vtables are safe to devirtualize, and we will optionally convert the metadata to hidden visibility at link time. Subsequent follow on patches will help enable this by adding vcall_visibility metadata to the ThinLTO summaries, and always emit type test intrinsics under -fwhole-program-vtables (and not just for vtables with hidden visibility). In order to do this safely with VFE, since for VFE all vtable loads must be type checked loads which will no longer be the case, this patch adds a new "Virtual Function Elim" module flag to communicate to GlobalDCE whether to perform VFE using the vcall_visibility metadata. One additional advantage of using the vcall_visibility metadata to drive more WPD at LTO link time is that we can use the same mechanism to enable more aggressive VFE at LTO link time as well. The link time option proposed in the RFC will convert vcall_visibility metadata to hidden (aka linkage unit visibility), which combined with -fvirtual-function-elimination will allow it to be done more aggressively at LTO link time under the same conditions. Reviewers: pcc, ostannard, evgeny777, steven_wu Subscribers: mehdi_amini, Prazek, hiraditya, dexonsmith, davidxl, cfe-commits, llvm-commits Tags: #clang, #llvm Differential Revision: https://reviews.llvm.org/D71907
49 lines
2.0 KiB
LLVM
49 lines
2.0 KiB
LLVM
; RUN: opt < %s -globaldce -S | FileCheck %s
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; We currently only use llvm.type.checked.load for virtual function pointers,
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; not any other part of the vtable, so we can't remove the RTTI pointer even if
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; it's never going to be loaded from.
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target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
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%struct.A = type { i32 (...)** }
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; CHECK: @_ZTV1A = hidden unnamed_addr constant { [3 x i8*] } { [3 x i8*] [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTI1A to i8*), i8* null] }, align 8, !type !0, !type !1, !vcall_visibility !2
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@_ZTV1A = hidden unnamed_addr constant { [3 x i8*] } { [3 x i8*] [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTI1A to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A3fooEv to i8*)] }, align 8, !type !0, !type !1, !vcall_visibility !2
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@_ZTS1A = hidden constant [3 x i8] c"1A\00", align 1
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@_ZTI1A = hidden constant { i8*, i8* } { i8* bitcast (i8** getelementptr inbounds (i8*, i8** @_ZTVN10__cxxabiv117__class_type_infoE, i64 2) to i8*), i8* getelementptr inbounds ([3 x i8], [3 x i8]* @_ZTS1A, i32 0, i32 0) }, align 8
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define internal void @_ZN1AC2Ev(%struct.A* %this) {
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entry:
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%0 = getelementptr inbounds %struct.A, %struct.A* %this, i64 0, i32 0
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store i32 (...)** bitcast (i8** getelementptr inbounds ({ [3 x i8*] }, { [3 x i8*] }* @_ZTV1A, i64 0, inrange i32 0, i64 2) to i32 (...)**), i32 (...)*** %0, align 8
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ret void
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}
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; CHECK-NOT: define {{.*}} @_ZN1A3fooEv(
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define internal void @_ZN1A3fooEv(%struct.A* nocapture %this) {
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entry:
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ret void
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}
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define dso_local i8* @_Z6make_Av() {
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entry:
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%call = tail call i8* @_Znwm(i64 8)
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%0 = bitcast i8* %call to %struct.A*
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tail call void @_ZN1AC2Ev(%struct.A* %0)
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ret i8* %call
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}
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declare dso_local noalias nonnull i8* @_Znwm(i64)
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@_ZTVN10__cxxabiv117__class_type_infoE = external dso_local global i8*
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!llvm.module.flags = !{!3, !4}
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!0 = !{i64 16, !"_ZTS1A"}
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!1 = !{i64 16, !"_ZTSM1AFvvE.virtual"}
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!2 = !{i64 2} ; translation-unit vcall visibility
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!3 = !{i32 1, !"LTOPostLink", i32 1}
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!4 = !{i32 1, !"Virtual Function Elim", i32 1}
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