[Assignment Tracking][22/*] Add loop-deletion test

The Assignment Tracking debug-info feature is outlined in this RFC:

https://discourse.llvm.org/t/
rfc-assignment-tracking-a-better-way-of-specifying-variable-locations-in-ir

This test covers the NFC-for-normal-debug-info change D133303.

Reviewed By: jmorse

Differential Revision: https://reviews.llvm.org/D133319

Author: OCHyams

llvm/test/DebugInfo/Generic/assignment-tracking/loop-deletion/dead-loop.ll

@@ -0,0 +1,79 @@
+; RUN: opt %s -passes=loop-deletion -S -o - -experimental-assignment-tracking \
+; RUN: | FileCheck %s
+
+;; $ cat test.cpp:
+;; void esc(int*);
+;; void fun() {
+;;   int Counter = 0;
+;;   for (; Counter < 2; Counter++) {}
+;;   esc(&Counter);
+;; }
+;;
+;; IR grabbed before loop-deletion in:
+;; $ clang++ -O2 -g -Xclang -fexperimental-assignment-tracking
+;;
+;; for.cond is a dead loop - the debug intrinsic inside will be moved to the
+;; exit block (and made undef) and then the loop will be deleted. Ensure that
+;; the dbg.assign intrinsic doesn't get transformed into a dbg.value by
+;; mistake.
+
+; CHECK: for.end:
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i32 undef,{{.+}}, metadata !DIExpression({{.+}}), metadata ![[ID:[0-9]+]], metadata ptr %Counter, metadata !DIExpression())
+; CHECK-NEXT: store i32 2, ptr %Counter, align 4,{{.*}}!DIAssignID ![[ID]]
+
+define dso_local void @_Z3funv() local_unnamed_addr #0 !dbg !7 {
+entry:
+  %Counter = alloca i32, align 4, !DIAssignID !13
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !11, metadata !DIExpression(), metadata !13, metadata ptr %Counter, metadata !DIExpression()), !dbg !14
+  call void @llvm.dbg.assign(metadata i32 0, metadata !11, metadata !DIExpression(), metadata !16, metadata ptr %Counter, metadata !DIExpression()), !dbg !14
+  br label %for.cond, !dbg !17
+
+for.cond:                                         ; preds = %for.cond, %entry
+  call void @llvm.dbg.assign(metadata i32 undef, metadata !11, metadata !DIExpression(DW_OP_plus_uconst, 1, DW_OP_stack_value), metadata !16, metadata ptr %Counter, metadata !DIExpression()), !dbg !14
+  br i1 false, label %for.cond, label %for.end, !dbg !18, !llvm.loop !20
+
+for.end:                                          ; preds = %for.cond
+  store i32 2, ptr %Counter, align 4, !dbg !14, !DIAssignID !16
+  call void @_Z3escPi(ptr noundef nonnull %Counter), !dbg !27
+  ret void, !dbg !28
+}
+
+declare void @llvm.lifetime.start.p0i8(i64 immarg, ptr nocapture)
+declare !dbg !29 dso_local void @_Z3escPi(ptr noundef) local_unnamed_addr
+declare void @llvm.lifetime.end.p0i8(i64 immarg, ptr nocapture)
+declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 14.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 7, !"uwtable", i32 1}
+!6 = !{!"clang version 14.0.0)"}
+!7 = distinct !DISubprogram(name: "fun", linkageName: "_Z3funv", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !10)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !{!11}
+!11 = !DILocalVariable(name: "Counter", scope: !7, file: !1, line: 3, type: !12)
+!12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!13 = distinct !DIAssignID()
+!14 = !DILocation(line: 0, scope: !7)
+!15 = !DILocation(line: 3, column: 3, scope: !7)
+!16 = distinct !DIAssignID()
+!17 = !DILocation(line: 4, column: 3, scope: !7)
+!18 = !DILocation(line: 4, column: 3, scope: !19)
+!19 = distinct !DILexicalBlock(scope: !7, file: !1, line: 4, column: 3)
+!20 = distinct !{!20, !18, !21, !22}
+!21 = !DILocation(line: 4, column: 35, scope: !19)
+!22 = !{!"llvm.loop.mustprogress"}
+!27 = !DILocation(line: 5, column: 3, scope: !7)
+!28 = !DILocation(line: 6, column: 1, scope: !7)
+!29 = !DISubprogram(name: "esc", linkageName: "_Z3escPi", scope: !1, file: !1, line: 1, type: !30, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !33)
+!30 = !DISubroutineType(types: !31)
+!31 = !{null, !32}
+!32 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+!33 = !{}