Fix LDV InstrRefBasedImpl to not crash when encountering unreachable blocks

llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp

@@ -318,6 +318,8 @@ class TransferTracker {
     for (auto Location : MTracker->locations()) {
       LocIdx Idx = Location.Idx;
       ValueIDNum &VNum = MLocs[Idx.asU64()];
+      if (VNum == ValueIDNum::EmptyValue)
+        continue;
       VarLocs.push_back(VNum);
 
       // Is there a variable that wants a location for this value? If not, skip.
@@ -2970,12 +2972,17 @@ void InstrRefBasedLDV::initialSetup(MachineFunction &MF) {
   // Compute mappings of block <=> RPO order.
   ReversePostOrderTraversal<MachineFunction *> RPOT(&MF);
   unsigned int RPONumber = 0;
-  for (MachineBasicBlock *MBB : RPOT) {
+  auto processMBB = [&](MachineBasicBlock *MBB) {
     OrderToBB[RPONumber] = MBB;
     BBToOrder[MBB] = RPONumber;
     BBNumToRPO[MBB->getNumber()] = RPONumber;
     ++RPONumber;
-  }
+  };
+  for (MachineBasicBlock *MBB : RPOT)
+    processMBB(MBB);
+  for (MachineBasicBlock &MBB : MF)
+    if (BBToOrder.find(&MBB) == BBToOrder.end())
+      processMBB(&MBB);
 
   // Order value substitutions by their "source" operand pair, for quick lookup.
   llvm::sort(MF.DebugValueSubstitutions);

llvm/test/DebugInfo/MIR/X86/ldv_unreachable_blocks.mir

@@ -0,0 +1,38 @@
+# RUN: llc -mtriple=x86_64-apple-macos %s -start-before=livedebugvalues -filetype=obj -o - | llvm-dwarfdump - | FileCheck %s
+# CHECK: DW_TAG_subprogram
+# Test that LiveDebugValues can handle MBBs that are not reachable in a RPOT.
+--- |
+  define hidden zeroext i1 @__foo_block_invoke(i8* nocapture noundef readonly %.block_descriptor, i64 noundef %type) !dbg !5 {
+  entry:
+    %call2.i = tail call zeroext i8 @foo_len(), !dbg !10
+    %cmp.i102.i = icmp ult i8 %call2.i, 64, !dbg !10
+    br i1 %cmp.i102.i, label %bar_length.exit105.i, label %if.else.i103.i, !dbg !10
+  if.else.i103.i:                                   ; preds = %sw.bb.i
+    br label %bar_length.exit105.i
+  bar_length.exit105.i:                        ; preds = %if.else.i103.i, %sw.bb.i
+    unreachable
+  baz_size.exit:                  ; preds = %bar_length.exit131.i, %bar_length.exit105.i, %bar_length.exit.i.baz_size.exit_crit_edge
+    unreachable
+  }
+  declare zeroext i8 @foo_len() local_unnamed_addr
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!3, !4}
+  !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !6, producer: "Apple clang", isOptimized: true, flags: "-fsanitize=fuzzer-no-link,address", runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !2, globals: !2, splitDebugInlining: false, nameTableKind: None, sysroot: "/", sdk: "MacOSX.sdk")
+  !2 = !{}
+  !3 = !{i32 2, !"Debug Info Version", i32 3}
+  !4 = !{i32 1, !"LTOPostLink", i32 1}
+  !5 = distinct !DISubprogram(name: "__foo_block_invoke", linkageName: "__foo_block_invoke", scope: !6, file: !6, line: 557, type: !7, scopeLine: 557, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+  !6 = !DIFile(filename: "t.c", directory: "")
+  !7 = !DISubroutineType(types: !2)
+  !10 = !DILocation(line: 558, column: 7, scope: !12)
+  !12 = distinct !DILexicalBlock(scope: !5, file: !6, line: 557, column: 50)
+name:            __foo_block_invoke
+body:             |
+  bb.0.entry:
+    JCC_1 %bb.1, 5, implicit $eflags, debug-location !10
+  bb.28.baz_size.exit:
+    RET64 $al, debug-location !10
+  bb.1:
+    successors: 
+  bb.25.if.else.i103.i (address-taken):
+    JMP_1 %bb.28

llvm/test/DebugInfo/MIR/X86/ldv_unreachable_blocks2.mir

@@ -0,0 +1,32 @@
+# RUN: llc -mtriple=x86_64-apple-macos %s -start-before=livedebugvalues -filetype=obj -o - | llvm-dwarfdump - | FileCheck %s
+# CHECK: DW_TAG_subprogram
+# Test that LiveDebugValues can handle MBBs that are not reachable in a RPOT.
+--- |
+  define hidden zeroext i1 @__foo_block_invoke(i8* nocapture noundef readonly %.block_descriptor, i64 noundef %type) !dbg !7 {
+  entry:
+    unreachable
+  do.body.i129.i:                                   ; preds = %if.else6.i128.i
+    unreachable
+  }
+  !llvm.dbg.cu = !{!3}
+  !llvm.module.flags = !{!5, !6}
+  !2 = !{}
+  !3 = distinct !DICompileUnit(language: DW_LANG_C99, file: !4, producer: "clang", runtimeVersion: 0, emissionKind: FullDebug)
+  !4 = !DIFile(filename: "t.c", directory: "/")
+  !5 = !{i32 2, !"Debug Info Version", i32 3}
+  !6 = !{i32 1, !"LTOPostLink", i32 1}
+  !7 = distinct !DISubprogram(name: "__foo_block_invoke", scope: !4, file: !4, line: 573, type: !9, scopeLine: 573, flags: DIFlagPrototyped, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !3, retainedNodes: !2)
+  !9 = !DISubroutineType(types: !2)
+  !11 = !DILocalVariable(name: ".block_descriptor", arg: 1, scope: !7, file: !4, line: 557, type: !12, flags: DIFlagArtificial)
+  !12 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
+  !13 = !DICompositeType(tag: DW_TAG_structure_type, name: "__block_literal_1", scope: !4, file: !4, line: 557, size: 392, elements: !2)
+  !15 = !DILocation(line: 558, column: 7, scope: !7)
+name:            __foo_block_invoke
+body:             |
+  bb.0.entry:
+    DBG_VALUE $rdi, $noreg, !11, !DIExpression(), debug-location !15
+    $ecx = MOV32rr undef $edi, implicit $dil, debug-location !15
+  bb.2:
+    successors: 
+    TRAP
+  bb.21.do.body.i129.i (address-taken):