[llvm] r373720 - [DebugInfo] LiveDebugValues: defer DBG_VALUE creation during analysis
Jeremy Morse via llvm-commits
llvm-commits at lists.llvm.org
Fri Oct 4 02:38:05 PDT 2019
Author: jmorse
Date: Fri Oct 4 02:38:05 2019
New Revision: 373720
URL: http://llvm.org/viewvc/llvm-project?rev=373720&view=rev
Log:
[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
Added:
llvm/trunk/test/DebugInfo/MIR/X86/live-debug-values-bad-transfer.mir
Modified:
llvm/trunk/lib/CodeGen/LiveDebugValues.cpp
Modified: llvm/trunk/lib/CodeGen/LiveDebugValues.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/LiveDebugValues.cpp?rev=373720&r1=373719&r2=373720&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/LiveDebugValues.cpp (original)
+++ llvm/trunk/lib/CodeGen/LiveDebugValues.cpp Fri Oct 4 02:38:05 2019
@@ -986,9 +986,6 @@ bool LiveDebugValues::transferTerminator
const VarLocMap &VarLocIDs) {
bool Changed = false;
- if (OpenRanges.empty())
- return false;
-
LLVM_DEBUG(for (unsigned ID
: OpenRanges.getVarLocs()) {
// Copy OpenRanges to OutLocs, if not already present.
@@ -1362,11 +1359,6 @@ bool LiveDebugValues::ExtendRanges(Machi
DebugEntryVals, OverlapFragments, SeenFragments);
OLChanged |= transferTerminator(MBB, OpenRanges, OutLocs, VarLocIDs);
- // Add any DBG_VALUE instructions necessitated by spills.
- for (auto &TR : Transfers)
- MBB->insertAfterBundle(TR.TransferInst->getIterator(), TR.DebugInst);
- Transfers.clear();
-
LLVM_DEBUG(printVarLocInMBB(MF, OutLocs, VarLocIDs,
"OutLocs after propagating", dbgs()));
LLVM_DEBUG(printVarLocInMBB(MF, InLocs, VarLocIDs,
@@ -1387,6 +1379,13 @@ bool LiveDebugValues::ExtendRanges(Machi
assert(Pending.empty() && "Pending should be empty");
}
+ // Add any DBG_VALUE instructions created by location transfers.
+ for (auto &TR : Transfers) {
+ auto *MBB = TR.TransferInst->getParent();
+ MBB->insertAfterBundle(TR.TransferInst->getIterator(), TR.DebugInst);
+ }
+ Transfers.clear();
+
// Deferred inlocs will not have had any DBG_VALUE insts created; do
// that now.
flushPendingLocs(PendingInLocs, VarLocIDs);
Added: llvm/trunk/test/DebugInfo/MIR/X86/live-debug-values-bad-transfer.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/MIR/X86/live-debug-values-bad-transfer.mir?rev=373720&view=auto
==============================================================================
--- llvm/trunk/test/DebugInfo/MIR/X86/live-debug-values-bad-transfer.mir (added)
+++ llvm/trunk/test/DebugInfo/MIR/X86/live-debug-values-bad-transfer.mir Fri Oct 4 02:38:05 2019
@@ -0,0 +1,103 @@
+# RUN: llc %s -mtriple=x86_64-unknown-unknown -o - -run-pass=livedebugvalues | FileCheck %s --implicit-check-not=DBG_VALUE
+#
+# Test that the DBG_VALUE of ecx below does not get propagated. It is considered
+# live-in on LiveDebugValues' first pass through the loop, but on the second it
+# should be removed from the InLocs set because it gets clobbered inside the
+# loop. There should be no transfer from ecx to ebx -- this is ensured by the
+# FileCheck implicit-check-not option.
+#
+# FIXME: we successfully prevent the false location (ebx) from being
+# propagated into block 2, but the original transfer isn't yet eliminated.
+# Thus we get no DBG_VALUe in block 2, but an invalid one in block 1.
+#
+# CHECK-LABEL: name: foo
+# CHECK-LABEL: bb.0.entry:
+# CHECK: $ecx = MOV32ri 0
+# CHECK-NEXT: DBG_VALUE
+# CHECK-LABEL: bb.1.loop:
+# CHECK: $ebx = COPY killed $ecx
+# CHECK-NEXT: DBG_VALUE
+
+--- |
+ source_filename = "live-debug-values-remove-range.ll"
+ target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+ declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+ define i32 @foo(i32 %bar) !dbg !4 {
+ entry:
+ br label %loop
+ loop:
+ br label %loop
+ exit:
+ ret i32 %bar
+ }
+
+ !llvm.module.flags = !{!0, !1}
+ !llvm.dbg.cu = !{!2}
+
+ !0 = !{i32 2, !"Debug Info Version", i32 3}
+ !1 = !{i32 2, !"Dwarf Version", i32 4}
+ !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "beards", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+ !3 = !DIFile(filename: "bees.cpp", directory: ".")
+ !4 = distinct !DISubprogram(name: "nope", scope: !3, file: !3, line: 1, type: !5, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !8)
+ !5 = !DISubroutineType(types: !6)
+ !6 = !{!7}
+ !7 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+ !8 = !{!9}
+ !9 = !DILocalVariable(name: "thin", scope: !4, file: !3, line: 1, type: !7)
+ !10 = !DILocation(line: 1, scope: !4)
+
+...
+---
+name: foo
+alignment: 4
+tracksRegLiveness: true
+liveins:
+ - { reg: '$edi' }
+frameInfo:
+ stackSize: 8
+ offsetAdjustment: -8
+ maxAlignment: 1
+ adjustsStack: true
+ hasCalls: true
+ maxCallFrameSize: 0
+ cvBytesOfCalleeSavedRegisters: 8
+fixedStack:
+ - { id: 0, type: spill-slot, offset: -16, size: 8, alignment: 16, callee-saved-register: '$rbx' }
+machineFunctionInfo: {}
+body: |
+ bb.0.entry:
+ liveins: $edi, $rbx
+
+ frame-setup PUSH64r killed $rbx, implicit-def $rsp, implicit $rsp
+ CFI_INSTRUCTION def_cfa_offset 16
+ CFI_INSTRUCTION offset $rbx, -16
+ $ebx = MOV32rr $edi
+ $eax = MOV32ri 0
+ $ecx = MOV32ri 0
+ DBG_VALUE $ecx, $noreg, !9, !DIExpression(), debug-location !10
+ $edi = MOV32ri 0
+ $esi = MOV32ri 0
+
+ bb.1.loop:
+ successors: %bb.1, %bb.2
+ liveins: $ebx, $eax, $ecx, $edi, $esi
+
+ $eax = COPY $ecx
+ $ebx = COPY killed $ecx
+ $ecx = COPY killed $edi
+ $edi = COPY killed $esi
+ $esi = MOV32ri 1
+ TEST8ri killed renamable $al, 1, implicit-def $eflags
+ JCC_1 %bb.1, 5, implicit killed $eflags
+
+ bb.2.exit:
+ liveins: $ebx
+
+ $eax = MOV32rr killed $ebx
+ $rbx = frame-destroy POP64r implicit-def $rsp, implicit $rsp
+ CFI_INSTRUCTION def_cfa_offset 8
+ RETQ $eax
+
+...
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