[SEH][CodeGen] Add test to track CFG optimization bug for SEH (#77441)

LiveDebugValues requires CFG only has one entry. BranchFolding and
MachineBlockPlacement may remove all predecessors of landing pad which
leaves it to be another entry.

Author: HaohaiWen

llvm/test/CodeGen/X86/windows-seh-EHa-PreserveCFG.ll

@@ -0,0 +1,81 @@
+; XFAIL: *
+; RUN: llc -mtriple=x86_64-pc-windows-msvc %s
+define dso_local void @main(ptr %addr, ptr %src, ptr %dst) personality ptr @__CxxFrameHandler3 !dbg !11 {
+entry:
+  %tmp0 = load float, ptr %src
+  %src1 = getelementptr inbounds float, ptr %src, i64 1
+  %tmp1 = load float, ptr %src1
+  %src2 = getelementptr inbounds float, ptr %src, i64 2
+  %tmp2 = load float, ptr %src2
+  %src3 = getelementptr inbounds float, ptr %src, i64 3
+  %tmp3 = load float, ptr %src3
+  %src4 = getelementptr inbounds float, ptr %src, i64 4
+  %tmp4 = load float, ptr %src4
+  %src5 = getelementptr inbounds float, ptr %src, i64 5
+  %tmp5 = load float, ptr %src5
+  %src6 = getelementptr inbounds float, ptr %src, i64 6
+  %tmp6 = load float, ptr %src6
+  invoke void @foo(ptr %addr)
+          to label %scope_begin unwind label %ehcleanup1, !dbg !13
+
+scope_begin:
+  invoke void @llvm.seh.scope.begin()
+          to label %scope_end unwind label %ehcleanup, !dbg !13
+
+scope_end:
+  invoke void @llvm.seh.scope.end()
+          to label %finish unwind label %ehcleanup, !dbg !13
+
+ehcleanup:
+  %0 = cleanuppad within none [], !dbg !13
+  call void @llvm.dbg.value(metadata ptr %addr, metadata !12, metadata !DIExpression()), !dbg !13
+  call void @foo(ptr %addr) [ "funclet"(token %0) ], !dbg !13
+  cleanupret from %0 unwind label %ehcleanup1, !dbg !13
+
+ehcleanup1:
+  %1 = cleanuppad within none [], !dbg !13
+  call void @foo(ptr %addr) [ "funclet"(token %1) ], !dbg !13
+  cleanupret from %1 unwind to caller, !dbg !13
+
+finish:
+  store float %tmp0, ptr %dst
+  %dst1 = getelementptr inbounds float, ptr %dst, i64 1
+  store float %tmp1, ptr %dst1
+  %dst2 = getelementptr inbounds float, ptr %dst, i64 2
+  store float %tmp2, ptr %dst2
+  %dst3 = getelementptr inbounds float, ptr %dst, i64 3
+  store float %tmp3, ptr %dst3
+  %dst4 = getelementptr inbounds float, ptr %dst, i64 4
+  store float %tmp4, ptr %dst4
+  %dst5 = getelementptr inbounds float, ptr %dst, i64 5
+  store float %tmp5, ptr %dst5
+  %dst6 = getelementptr inbounds float, ptr %dst, i64 6
+  store float %tmp6, ptr %dst6
+  ret void
+}
+
+declare dso_local void @llvm.seh.scope.begin()
+declare dso_local void @llvm.seh.scope.end()
+declare dso_local i32 @__CxxFrameHandler3(...)
+declare dso_local void @foo(ptr %addr)
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.module.flags = !{!0, !1, !2, !3}
+!llvm.dbg.cu = !{!14}
+
+!0 = !{i32 2, !"eh-asynch", i32 1}
+!1 = !{i32 2, !"CodeView", i32 1}
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = !{i32 7, !"uwtable", i32 2}
+
+!4 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
+!5 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !4, size: 64)
+!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!7 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !6, size: 64)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !7, !5, !5}
+!10 = !DIFile(filename: "c:/main.cpp", directory: "")
+!11 = distinct !DISubprogram(name: "main", scope: !10, file: !10, line: 5, type: !8, scopeLine: 11, unit: !14)
+!12 = !DILocalVariable(name: "addr", scope: !11, file: !10, line: 5, type: !7)
+!13 = !DILocation(line: 7, scope: !11)
+!14 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !10, isOptimized: true, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)