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[ThinLTO] Remove dead and dropped symbol declarations when possible
Summary: Removing the dropped symbols will prevent indirect call promotion in the ThinLTO Backend from adding a new reference to a symbol, which can result in linker unsats. This can happen when we compile with a sample profile collected from one binary by used for another, which may have profiled targets that aren't used in the new binary. Note that until dropDeadSymbols handles variables and aliases (in progress), we may not be able to remove the declaration and can still have an issue. Reviewers: grimar, davidxl Subscribers: mehdi_amini, inglorion, llvm-commits, eraman Differential Revision: https://reviews.llvm.org/D42816 llvm-svn: 324299
This commit is contained in:
Teresa Johnson
parent
2884049a25
commit
1003e07d66
@ -401,14 +401,23 @@ Error lto::backend(Config &C, AddStreamFn AddStream,
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static void dropDeadSymbols(Module &Mod, const GVSummaryMapTy &DefinedGlobals,
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const ModuleSummaryIndex &Index) {
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std::vector<GlobalValue *> ReplacedGlobals;
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std::vector<GlobalValue*> DeadGVs;
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for (auto &GV : Mod.global_values())
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if (GlobalValueSummary *GVS = DefinedGlobals.lookup(GV.getGUID()))
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if (!Index.isGlobalValueLive(GVS) && !convertToDeclaration(GV))
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ReplacedGlobals.push_back(&GV);
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if (!Index.isGlobalValueLive(GVS)) {
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DeadGVs.push_back(&GV);
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convertToDeclaration(GV);
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}
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for (GlobalValue *GV : ReplacedGlobals)
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// Now that all dead bodies have been dropped, delete the actual objects
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// themselves when possible.
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for (GlobalValue *GV : DeadGVs) {
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GV->removeDeadConstantUsers();
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// Might reference something defined in native object (i.e. dropped a
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// non-prevailing IR def, but we need to keep the declaration).
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if (GV->use_empty())
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GV->eraseFromParent();
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}
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}
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Error lto::thinBackend(Config &Conf, unsigned Task, AddStreamFn AddStream,
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@ -50,7 +50,7 @@
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; LTO2: define internal void @_GLOBAL__I_a()
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; LTO2: define internal void @bar() {
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; LTO2: define internal void @bar_internal()
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; LTO2: declare dso_local void @dead_func()
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; LTO2-NOT: @dead_func()
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; LTO2-NOT: available_externally {{.*}} @baz()
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; Make sure we didn't internalize @boo, which is reachable via
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@ -0,0 +1,71 @@
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; REQUIRES: x86-registered-target
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; RUN: opt -module-summary %s -o %t.bc
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; Tests that with dead stripping in the thin link enabled (default), we do not
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; promote to target of the dropped dead symbol _ZL3foov. This can happen with a
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; sample profile collected for one binary used to optimize for another binary.
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; RUN: llvm-lto2 run -save-temps -o %t2 %t.bc -r %t.bc,fptr,plx \
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; RUN: -r %t.bc,main,plx -r %t.bc,_ZL3foov,l
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; RUN: llvm-dis < %t2.1.4.opt.bc | FileCheck %s --check-prefix=OPT
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; RUN: llvm-lto2 run -save-temps -o %t2 %t.bc -r %t.bc,fptr,plx \
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; RUN: -r %t.bc,main,plx -r %t.bc,_ZL3foov,l -compute-dead=false
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; RUN: llvm-dis < %t2.1.4.opt.bc | FileCheck %s --check-prefix=OPT-NODEAD
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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@fptr = local_unnamed_addr global void ()* null, align 8
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define void @_ZL3foov() #1 {
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entry:
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ret void
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}
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define i32 @main() local_unnamed_addr #0 !prof !34 {
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entry:
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%0 = load void ()*, void ()** @fptr, align 8
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; OPT-NOT: label %if.false.orig_indirect
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; OPT-NODEAD: br i1 %{{[0-9]+}}, label %if.end.icp, label %if.false.orig_indirect
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tail call void %0(), !prof !40
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ret i32 0
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}
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!3,!4}
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!llvm.ident = !{!31}
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!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 5.0.0 (trunk 297016)", isOptimized: true, runtimeVersion: 0, emissionKind: NoDebug, enums: !2)
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!1 = !DIFile(filename: "main.cc", directory: ".")
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!2 = !{}
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!3 = !{i32 2, !"Debug Info Version", i32 3}
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!4 = !{i32 1, !"ProfileSummary", !5}
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!5 = !{!6, !7, !8, !9, !10, !11, !12, !13}
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!6 = !{!"ProfileFormat", !"SampleProfile"}
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!7 = !{!"TotalCount", i64 3003}
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!8 = !{!"MaxCount", i64 3000}
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!9 = !{!"MaxInternalCount", i64 0}
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!10 = !{!"MaxFunctionCount", i64 0}
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!11 = !{!"NumCounts", i64 3}
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!12 = !{!"NumFunctions", i64 1}
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!13 = !{!"DetailedSummary", !14}
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!14 = !{!15, !16, !17, !18, !19, !20, !20, !21, !21, !22, !23, !24, !25, !26, !27, !28, !29, !30}
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!15 = !{i32 10000, i64 3000, i32 1}
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!16 = !{i32 100000, i64 3000, i32 1}
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!17 = !{i32 200000, i64 3000, i32 1}
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!18 = !{i32 300000, i64 3000, i32 1}
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!19 = !{i32 400000, i64 3000, i32 1}
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!20 = !{i32 500000, i64 3000, i32 1}
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!21 = !{i32 600000, i64 3000, i32 1}
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!22 = !{i32 700000, i64 3000, i32 1}
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!23 = !{i32 800000, i64 3000, i32 1}
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!24 = !{i32 900000, i64 3000, i32 1}
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!25 = !{i32 950000, i64 3000, i32 1}
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!26 = !{i32 990000, i64 3000, i32 1}
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!27 = !{i32 999000, i64 3000, i32 1}
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!28 = !{i32 999900, i64 2, i32 2}
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!29 = !{i32 999990, i64 2, i32 2}
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!30 = !{i32 999999, i64 2, i32 2}
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!31 = !{!"clang version 5.0.0 (trunk 297016)"}
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!34 = !{!"function_entry_count", i64 1}
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!40 = !{!"VP", i32 0, i64 3000, i64 -8789629626369651636, i64 3000}
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@ -47,7 +47,7 @@ target triple = "x86_64-unknown-linux-gnu"
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; the expected internalization.
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; CHECK-REGULARLTO-DAG: @var_with_nonC_section = internal global i32 0, section ".nonCsection"
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; Check we dropped definition of dead variable.
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; CHECK-THINLTO-DAG: @var_with_nonC_section = external dso_local global i32, section ".nonCsection"
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; CHECK-THINLTO-NOT: @var_with_nonC_section
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@var_with_nonC_section = global i32 0, section ".nonCsection"
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; We should not internalize @deadfunc_with_section due to section
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@ -61,7 +61,7 @@ define void @deadfunc_with_section() section "some_other_section" {
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; the expected internalization.
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; CHECK2-REGULARLTO-DAG: define internal void @deadfunc_with_nonC_section() section ".nonCsection"
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; Check dead function converted to declaration.
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; CHECK-THINLTO-DAG: declare dso_local void @deadfunc_with_nonC_section() section ".nonCsection"
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; CHECK-THINLTO-NOT: @deadfunc_with_nonC_section()
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define void @deadfunc_with_nonC_section() section ".nonCsection" {
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call void @deadfunc2_called_from_nonC_section()
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ret void
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@ -80,5 +80,5 @@ declare void @deadfunc2_called_from_section()
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; are getting the expected internalization.
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; CHECK2-REGULARLTO: define internal void @deadfunc2_called_from_nonC_section
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; Check dead function converted to declaration.
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; CHECK2-THINLTO: declare dso_local void @deadfunc2_called_from_nonC_section
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; CHECK2-THINLTO-NOT: @deadfunc2_called_from_nonC_section
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declare void @deadfunc2_called_from_nonC_section()
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