Revert "[PHIEliminate] Move dbg values after phi and label"

Testing compiler-rt, a new assertion failure occurs when building
the GwpAsanTestObjects object. I'm uploading a reproducer to D70597.

This reverts commit 75188b01e9af3a89639d84be912f84610d6885ba.

lib/CodeGen/MachineVerifier.cpp

@@ -273,7 +273,6 @@ namespace {
     void markReachable(const MachineBasicBlock *MBB);
     void calcRegsPassed();
     void checkPHIOps(const MachineBasicBlock &MBB);
-    void checkPHIDbg(const MachineBasicBlock &MBB);
 
     void calcRegsRequired();
     void verifyLiveVariables();
@@ -2263,31 +2262,11 @@ void MachineVerifier::checkPHIOps(const MachineBasicBlock &MBB) {
   }
 }
 
-// Check there must be no DBG_VALUEs between PHIs and LABELs, so that
-// the PHIs could lower after LABELs successfully without dbg barriers.
-void MachineVerifier::checkPHIDbg(const MachineBasicBlock &MBB) {
-
-  // Quick exit for basic blocks without PHIs.
-  if (MBB.empty() || !MBB.front().isPHI())
-    return;
-
-  MachineBasicBlock &MBB2 = const_cast<MachineBasicBlock &>(MBB);
-  MachineBasicBlock::iterator LastPHIIt =
-    std::prev(MBB2.SkipPHIsAndLabels(MBB2.begin()));
-  // Backward to skip debug if the lastPHIIt is DBG_VALUE, the LastPHIIt
-  // should be the same if no DBG_VALUEs between PHIs and LABELs.
-  if (LastPHIIt != skipDebugInstructionsBackward(
-          std::prev(MBB2.SkipPHIsLabelsAndDebug(MBB2.begin())), MBB2.begin()))
-    report("Unexpected DBG_VALUEs between PHI and LABEL", &MBB2);
-}
-
 void MachineVerifier::visitMachineFunctionAfter() {
   calcRegsPassed();
 
-  for (const MachineBasicBlock &MBB : *MF) {
+  for (const MachineBasicBlock &MBB : *MF)
     checkPHIOps(MBB);
-    checkPHIDbg(MBB);
-  }
 
   // Now check liveness info if available
   calcRegsRequired();

lib/CodeGen/PHIElimination.cpp

@@ -210,11 +210,6 @@ bool PHIElimination::EliminatePHINodes(MachineFunction &MF,
   MachineBasicBlock::iterator LastPHIIt =
     std::prev(MBB.SkipPHIsAndLabels(MBB.begin()));
 
-  assert((LastPHIIt == skipDebugInstructionsBackward(
-            std::prev(MBB.SkipPHIsLabelsAndDebug(MBB.begin())),
-            MBB.begin())) &&
-         "There must be no DBG_VALUEs between PHI and LABEL");
-
   while (MBB.front().isPHI())
     LowerPHINode(MBB, LastPHIIt);
 

lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp

@@ -929,12 +929,10 @@ EmitSchedule(MachineBasicBlock::iterator &InsertPos) {
     }
   }
 
-  // Insert all the DBG_VALUEs which have not already been inserted in source
+  // Insert all the dbg_values which have not already been inserted in source
   // order sequence.
   if (HasDbg) {
-    // Always place DBG_VALUEs after all other special start-of-block
-    // instructions, to avoid debug data hiding start-of-block instructions.
-    MachineBasicBlock::iterator BBBegin = BB->SkipPHIsAndLabels(BB->begin());
+    MachineBasicBlock::iterator BBBegin = BB->getFirstNonPHI();
 
     // Sort the source order instructions and use the order to insert debug
     // values. Use stable_sort so that DBG_VALUEs are inserted in the same order

test/CodeGen/X86/dbg-changes-codegen-phi-elimination.ll

@@ -1,66 +0,0 @@
-; RUN: llc -O0 %s -mtriple=x86_64 -stop-after=phi-node-elimination -verify-machineinstrs -o - | FileCheck %s
-
-; Test that the DBG_VALUE must be after PHI and label, the PHI is converted to
-; a copy and lower after Label. The DBG_VALUE should not impact PHI lowering.
-; before:
-;    phi
-;    dbg_value
-;    label
-; after:
-;    LABEL
-;    COPY
-;    DBG_VALUE
-; Fix the issue: https://bugs.llvm.org/show_bug.cgi?id=43859
-
-define i32 @func(i32 %a0) personality void ()* @personality !dbg !9 {
-bb1:
-  %v = icmp slt i32 %a0, 0
-  br i1 %v, label %bb2, label %bb3
-
-bb2:
-  br label %bb3
-
-bb3:
-; CHECK: bb.2.bb3:
-; CHECK: EH_LABEL
-; CHECK-NEXT: %0:gr32 = COPY %7
-; CHECK-NEXT: DBG_VALUE %0
-  %0 = phi i32 [ 2, %bb2 ], [ 1, %bb1 ]
-  call void @llvm.dbg.value(metadata i32 %0, metadata !8, metadata !DIExpression()), !dbg !13
-  invoke void @foo() to label %end unwind label %lpad
-
-end:
-  ret i32 %0
-
-lpad:
-  %1 = landingpad { i8*, i32 }
-           cleanup
-  unreachable
-}
-
-declare void @foo()
-
-declare void @personality()
-
-; Function Attrs: nounwind readnone
-declare void @llvm.dbg.value(metadata, metadata, metadata)
-
-
-!llvm.dbg.cu = !{!0}
-!llvm.module.flags = !{!3, !4, !5, !6}
-!llvm.ident = !{!7}
-
-!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
-!1 = !DIFile(filename: "a.c", directory: "/tmp")
-!2 = !{}
-!3 = !{i32 2, !"Dwarf Version", i32 4}
-!4 = !{i32 2, !"Debug Info Version", i32 3}
-!5 = !{i32 1, !"wchar_size", i32 4}
-!6 = !{i32 1, !"min_enum_size", i32 4}
-!7 = !{!"clang"}
-!8 = !DILocalVariable(name: "c", scope: !9, file: !1, line: 3, type: !12)
-!9 = distinct !DISubprogram(name: "func", scope: !1, file: !1, line: 1, type: !10, scopeLine: 2, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
-!10 = !DISubroutineType(types: !11)
-!11 = !{!12, !12}
-!12 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
-!13 = !DILocation(line: 3, column: 13, scope: !9)