[DebugInfo][LSR] Add test for use of IV with a SCEV containing undef

Added a lit test that checks scev-based salvagaing does not select IVs
that have a SCEV containing an undef.

Original Differential Revision: https://reviews.llvm.org/D111810

Author: Chris Jackson

llvm/test/Transforms/LoopStrengthReduce/pr52161.ll

@@ -0,0 +1,54 @@
+; RUN: opt -S -loop-reduce %s | FileCheck %s
+
+;; Ensure that scev-based salvaging in LSR does not select an IV containing
+;; an 'undef' element.
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define i16 @n() !dbg !8 {
+entry:
+  br i1 undef, label %m, label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %iv = phi i16 [ %ivdec, %for.body ], [ 14, %entry ]
+  %ivdec = sub i16 %iv, 1
+  call void @llvm.dbg.value(metadata i16 %iv, metadata !21, metadata !DIExpression()), !dbg !19
+  br label %for.body
+
+m:                                                ; preds = %m, %entry
+  %0 = phi i16 [ 3, %m ], [ 6, %entry ]
+  %gg = add i16 %0, 23
+  ; CHECK: call void @llvm.dbg.value(metadata i16 undef, metadata !{{[0-9]+}}, metadata !DIExpression()),
+  call void @llvm.dbg.value(metadata i16 %0, metadata !14, metadata !DIExpression()), !dbg !19
+  br label %m
+}
+
+; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
+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 version 14.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "reduced.c", directory: "/")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 1}
+!6 = !{i32 7, !"frame-pointer", i32 2}
+!7 = !{!"clang version 14.0.0"}
+!8 = distinct !DISubprogram(name: "n", scope: !1, file: !1, line: 18, type: !9, scopeLine: 18, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
+!9 = !DISubroutineType(types: !10)
+!10 = !{!11}
+!11 = !DIBasicType(name: "int", size: 16, encoding: DW_ATE_signed)
+!12 = !{!13}
+!13 = !DILabel(scope: !8, name: "m", file: !1, line: 22)
+!14 = !DILocalVariable(name: "k", arg: 2, scope: !15, file: !1, line: 9, type: !11)
+!15 = distinct !DISubprogram(name: "i", scope: !1, file: !1, line: 9, type: !16, scopeLine: 9, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !18)
+!16 = !DISubroutineType(types: !17)
+!17 = !{!11, !11, !11}
+!18 = !{!14}
+!19 = !DILocation(line: 0, scope: !15, inlinedAt: !20)
+!20 = distinct !DILocation(line: 23, scope: !8)
+!21 = !DILocalVariable(name: "x", arg: 2, scope: !15, file: !1, line: 1, type: !11)