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[ThinLTO/WPD] Fix index-based WPD for alias vtables

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Summary:
A recent fix in D69452 fixed index based WPD in the presence of
available_externally vtables. It added a cast of the vtable def
summary to a GlobalVarSummary. However, in some cases one def may be an
alias, in which case we need to get the base object before casting,
otherwise we will crash.

Reviewers: evgeny777, steven_wu, aganea

Subscribers: mehdi_amini, inglorion, hiraditya, dexonsmith, arphaman, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71040
This commit is contained in:
Teresa Johnson 2019-12-04 17:15:10 -08:00
parent 99282e063a
commit 6720ba0105
3 changed files with 74 additions and 1 deletions
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2
lib/Transforms/IPO/WholeProgramDevirt.cpp
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@ -869,7 +869,7 @@ bool DevirtIndex::tryFindVirtualCallTargets(
LocalFound = true;
}
if (!GlobalValue::isAvailableExternallyLinkage(S->linkage()))
VS = cast<GlobalVarSummary>(S.get());
VS = cast<GlobalVarSummary>(S->getBaseObject());
}
if (!VS->isLive())
continue;

15
test/ThinLTO/X86/Inputs/devirt_alias.ll Normal file
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@ -0,0 +1,15 @@
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-grtev4-linux-gnu"
%struct.D = type { i32 (...)** }
@some_name = constant { [3 x i8*] } { [3 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.D*, i32)* @_ZN1D1mEi to i8*)] }, !type !3
@_ZTV1D = alias { [3 x i8*] }, { [3 x i8*] }* @some_name
define i32 @_ZN1D1mEi(%struct.D* %this, i32 %a) #0 {
ret i32 0;
}
attributes #0 = { noinline optnone }
!3 = !{i64 16, !"_ZTS1D"}

58
test/ThinLTO/X86/devirt_alias.ll Normal file
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@ -0,0 +1,58 @@
; REQUIRES: x86-registered-target
; Test index-based devirtualization when one copy is an alias.
; Generate unsplit module with summary for ThinLTO index-based WPD.
; RUN: opt -thinlto-bc -o %t3.o %s
; RUN: opt -thinlto-bc -o %t4.o %p/Inputs/devirt_alias.ll
; RUN: llvm-lto2 run %t3.o %t4.o -save-temps -pass-remarks=. \
; RUN: -wholeprogramdevirt-print-index-based \
; RUN: -o %t5 \
; RUN: -r=%t3.o,test,px \
; RUN: -r=%t3.o,_ZTV1D, \
; RUN: -r=%t3.o,_ZN1D1mEi, \
; RUN: -r=%t4.o,_ZN1D1mEi,p \
; RUN: -r=%t4.o,_ZTV1D,px \
; RUN: -r=%t4.o,some_name,px \
; RUN: 2>&1 | FileCheck %s --check-prefix=REMARK --check-prefix=PRINT
; RUN: llvm-dis %t5.1.4.opt.bc -o - | FileCheck %s --check-prefix=CHECK-IR1
; PRINT-DAG: Devirtualized call to {{.*}} (_ZN1D1mEi)
; REMARK-DAG: single-impl: devirtualized a call to _ZN1D1mEi
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-grtev4-linux-gnu"
%struct.D = type { i32 (...)** }
@_ZTV1D = linkonce_odr constant { [3 x i8*] } { [3 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.D*, i32)* @_ZN1D1mEi to i8*)] }, !type !3
; CHECK-IR1-LABEL: define i32 @test
define i32 @test(%struct.D* %obj2, i32 %a) {
entry:
%0 = bitcast %struct.D* %obj2 to i8***
%vtable2 = load i8**, i8*** %0
%1 = bitcast i8** %vtable2 to i8*
%p2 = call i1 @llvm.type.test(i8* %1, metadata !"_ZTS1D")
call void @llvm.assume(i1 %p2)
%2 = bitcast i8** %vtable2 to i32 (%struct.D*, i32)**
%fptr33 = load i32 (%struct.D*, i32)*, i32 (%struct.D*, i32)** %2, align 8
; Check that the call was devirtualized.
; CHECK-IR1: %call4 = tail call i32 @_ZN1D1mEi
%call4 = tail call i32 %fptr33(%struct.D* nonnull %obj2, i32 %a)
ret i32 %call4
}
; CHECK-IR1-LABEL: ret i32
; CHECK-IR1-LABEL: }
declare i1 @llvm.type.test(i8*, metadata)
declare void @llvm.assume(i1)
declare i32 @_ZN1D1mEi(%struct.D* %this, i32 %a)
attributes #0 = { noinline optnone }
!3 = !{i64 16, !"_ZTS1D"}