[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373720 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/LiveDebugValues.cpp b/lib/CodeGen/LiveDebugValues.cpp
index 0bdc62a345cbc2ca1c2a897d1b1cf8cc72b28969..8d523377fb40b5926fb176618159ee9334339bb4 100644 (file)
--- a/lib/CodeGen/LiveDebugValues.cpp
+++ b/lib/CodeGen/LiveDebugValues.cpp
@@ -986,9 +986,6 @@ bool LiveDebugValues::transferTerminator(MachineBasicBlock *CurMBB,
                                          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(MachineFunction &MF) {
                       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(MachineFunction &MF) {
     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);

diff --git a/test/DebugInfo/MIR/X86/live-debug-values-bad-transfer.mir b/test/DebugInfo/MIR/X86/live-debug-values-bad-transfer.mir
new file mode 100644 (file)
index 0000000..1d978b9
--- /dev/null
+++ b/test/DebugInfo/MIR/X86/live-debug-values-bad-transfer.mir
@@ -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
+
+...