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Revert r313157 "ThinLTO: Correctly follow aliasee references when dead stripping." 

This broke Chromium's CFI build; see crbug.com/765004.

> We were previously handling aliases during dead stripping by adding
> the aliased global's "original name" GUID to the worklist. This will
> lead to incorrect behaviour if the global has local linkage because
> the original name GUID will not correspond to the global's GUID in
> the summary.
>
> Because an alias is just another name for the global that it
> references, there is no need to mark the referenced global as used,
> or to follow references from any other copies of the global. So all
> we need to do is to follow references from the aliasee's summary
> instead of the alias.
>
> Differential Revision: https://reviews.llvm.org/D37789

llvm-svn: 313222
This commit is contained in:
Hans Wennborg 2017-09-14 00:40:14 +00:00
parent 3568319679
commit ae050afeb9
3 changed files with 8 additions and 29 deletions
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13
llvm/lib/Transforms/IPO/FunctionImport.cpp
View File

@ -488,14 +488,17 @@ void llvm::computeDeadSymbols(
while (!Worklist.empty()) {
auto VI = Worklist.pop_back_val();
for (auto &Summary : VI.getSummaryList()) {
GlobalValueSummary *Base = Summary.get();
if (auto *AS = dyn_cast<AliasSummary>(Base))
Base = &AS->getAliasee();
for (auto Ref : Base->refs())
for (auto Ref : Summary->refs())
visit(Ref);
if (auto *FS = dyn_cast<FunctionSummary>(Base))
if (auto *FS = dyn_cast<FunctionSummary>(Summary.get()))
for (auto Call : FS->calls())
visit(Call.first);
if (auto *AS = dyn_cast<AliasSummary>(Summary.get())) {
auto AliaseeGUID = AS->getAliasee().getOriginalName();
ValueInfo AliaseeVI = Index.getValueInfo(AliaseeGUID);
if (AliaseeVI)
visit(AliaseeVI);
}
}
}
Index.setWithGlobalValueDeadStripping();

4
llvm/test/LTO/Resolution/X86/Inputs/dead-strip-alias.ll
View File

@ -1,4 +0,0 @@
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@external = global i8 42

20
llvm/test/LTO/Resolution/X86/dead-strip-alias.ll
View File

@ -1,20 +0,0 @@
; RUN: opt -module-summary -o %t %s
; RUN: opt -module-summary -o %t2 %S/Inputs/dead-strip-alias.ll
; RUN: llvm-lto2 run %t -r %t,main,px -r %t,alias,p -r %t,external, \
; RUN: %t2 -r %t2,external,p \
; RUN: -save-temps -o %t3
; RUN: llvm-nm %t3.1 | FileCheck %s
; CHECK: D external
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@alias = alias i8*, i8** @internal
@internal = internal global i8* @external
@external = external global i8
define i8** @main() {
ret i8** @alias
}