forked from OSchip/llvm-project
[DebugInfo] LiveDebugValues: defer DBG_VALUE creation during analysis
When transfering variable locations from one place to another, LiveDebugValues immediately creates a DBG_VALUE representing that transfer. This causes trouble if the variable location should subsequently be invalidated by a loop back-edge, such as in the added test case: the transfer DBG_VALUE from a now-invalid location is used as proof that the variable location is correct. This is effectively a self-fulfilling prophesy. To avoid this, defer the insertion of transfer DBG_VALUEs until after analysis has completed. Some of those transfers are still sketchy, but we don't propagate them into other blocks now. Differential Revision: https://reviews.llvm.org/D67393 llvm-svn: 373720
This commit is contained in:
Jeremy Morse
parent
4128dc4500
commit
0ca48de26c
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@ -986,9 +986,6 @@ bool LiveDebugValues::transferTerminator(MachineBasicBlock *CurMBB,
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const VarLocMap &VarLocIDs) {
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bool Changed = false;
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if (OpenRanges.empty())
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return false;
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LLVM_DEBUG(for (unsigned ID
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: OpenRanges.getVarLocs()) {
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// Copy OpenRanges to OutLocs, if not already present.
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@ -1362,11 +1359,6 @@ bool LiveDebugValues::ExtendRanges(MachineFunction &MF) {
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DebugEntryVals, OverlapFragments, SeenFragments);
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OLChanged |= transferTerminator(MBB, OpenRanges, OutLocs, VarLocIDs);
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// Add any DBG_VALUE instructions necessitated by spills.
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for (auto &TR : Transfers)
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MBB->insertAfterBundle(TR.TransferInst->getIterator(), TR.DebugInst);
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Transfers.clear();
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LLVM_DEBUG(printVarLocInMBB(MF, OutLocs, VarLocIDs,
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"OutLocs after propagating", dbgs()));
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LLVM_DEBUG(printVarLocInMBB(MF, InLocs, VarLocIDs,
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@ -1387,6 +1379,13 @@ bool LiveDebugValues::ExtendRanges(MachineFunction &MF) {
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assert(Pending.empty() && "Pending should be empty");
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}
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// Add any DBG_VALUE instructions created by location transfers.
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for (auto &TR : Transfers) {
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auto *MBB = TR.TransferInst->getParent();
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MBB->insertAfterBundle(TR.TransferInst->getIterator(), TR.DebugInst);
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}
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Transfers.clear();
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// Deferred inlocs will not have had any DBG_VALUE insts created; do
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// that now.
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flushPendingLocs(PendingInLocs, VarLocIDs);
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@ -0,0 +1,103 @@
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# RUN: llc %s -mtriple=x86_64-unknown-unknown -o - -run-pass=livedebugvalues | FileCheck %s --implicit-check-not=DBG_VALUE
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#
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# Test that the DBG_VALUE of ecx below does not get propagated. It is considered
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# live-in on LiveDebugValues' first pass through the loop, but on the second it
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# should be removed from the InLocs set because it gets clobbered inside the
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# loop. There should be no transfer from ecx to ebx -- this is ensured by the
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# FileCheck implicit-check-not option.
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#
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# FIXME: we successfully prevent the false location (ebx) from being
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# propagated into block 2, but the original transfer isn't yet eliminated.
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# Thus we get no DBG_VALUe in block 2, but an invalid one in block 1.
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#
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# CHECK-LABEL: name: foo
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# CHECK-LABEL: bb.0.entry:
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# CHECK: $ecx = MOV32ri 0
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# CHECK-NEXT: DBG_VALUE
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# CHECK-LABEL: bb.1.loop:
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# CHECK: $ebx = COPY killed $ecx
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# CHECK-NEXT: DBG_VALUE
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--- |
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source_filename = "live-debug-values-remove-range.ll"
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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declare void @llvm.dbg.value(metadata, metadata, metadata)
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define i32 @foo(i32 %bar) !dbg !4 {
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entry:
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br label %loop
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loop:
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br label %loop
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exit:
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ret i32 %bar
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}
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!llvm.module.flags = !{!0, !1}
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!llvm.dbg.cu = !{!2}
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!0 = !{i32 2, !"Debug Info Version", i32 3}
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!1 = !{i32 2, !"Dwarf Version", i32 4}
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!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "beards", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
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!3 = !DIFile(filename: "bees.cpp", directory: ".")
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!4 = distinct !DISubprogram(name: "nope", scope: !3, file: !3, line: 1, type: !5, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !8)
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!5 = !DISubroutineType(types: !6)
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!6 = !{!7}
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!7 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
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!8 = !{!9}
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!9 = !DILocalVariable(name: "thin", scope: !4, file: !3, line: 1, type: !7)
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!10 = !DILocation(line: 1, scope: !4)
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...
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---
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name: foo
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alignment: 4
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tracksRegLiveness: true
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liveins:
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- { reg: '$edi' }
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frameInfo:
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stackSize: 8
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offsetAdjustment: -8
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maxAlignment: 1
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adjustsStack: true
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hasCalls: true
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maxCallFrameSize: 0
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cvBytesOfCalleeSavedRegisters: 8
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fixedStack:
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- { id: 0, type: spill-slot, offset: -16, size: 8, alignment: 16, callee-saved-register: '$rbx' }
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machineFunctionInfo: {}
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body: |
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bb.0.entry:
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liveins: $edi, $rbx
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frame-setup PUSH64r killed $rbx, implicit-def $rsp, implicit $rsp
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CFI_INSTRUCTION def_cfa_offset 16
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CFI_INSTRUCTION offset $rbx, -16
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$ebx = MOV32rr $edi
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$eax = MOV32ri 0
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$ecx = MOV32ri 0
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DBG_VALUE $ecx, $noreg, !9, !DIExpression(), debug-location !10
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$edi = MOV32ri 0
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$esi = MOV32ri 0
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bb.1.loop:
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successors: %bb.1, %bb.2
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liveins: $ebx, $eax, $ecx, $edi, $esi
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$eax = COPY $ecx
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$ebx = COPY killed $ecx
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$ecx = COPY killed $edi
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$edi = COPY killed $esi
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$esi = MOV32ri 1
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TEST8ri killed renamable $al, 1, implicit-def $eflags
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JCC_1 %bb.1, 5, implicit killed $eflags
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bb.2.exit:
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liveins: $ebx
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$eax = MOV32rr killed $ebx
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$rbx = frame-destroy POP64r implicit-def $rsp, implicit $rsp
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CFI_INSTRUCTION def_cfa_offset 8
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RETQ $eax
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...
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