[DebugInfo][RemoveDIs] Reverse order of DPValues from findDbgUsers (#74099)

The order of dbg.value intrinsics appearing in the output can affect the
order of tables in DWARF sections. This means that DPValues, our
dbg.value replacement, needs to obey the same ordering rules. For
dbg.values returned by findDbgUsers it's reverse order of creation (due
to how they're put on use-lists). Produce that order from findDbgUsers
for DPValues.

I've got a few IR files where the order of dbg.values flips, but it's a
fragile test -- ultimately it needs the number of times a DPValue is
handled by findDbgValues to be odd.

1 files changed, 65 insertions, 0 deletions

diff --git a/llvm/unittests/IR/DebugInfoTest.cpp b/llvm/unittests/IR/DebugInfoTest.cpp
index a408c0a..be8f590 100644
--- a/llvm/unittests/IR/DebugInfoTest.cpp
+++ b/llvm/unittests/IR/DebugInfoTest.cpp
@@ -284,6 +284,71 @@ TEST(MetadataTest, DeleteInstUsedByDPValue) {
   UseNewDbgInfoFormat = OldDbgValueMode;
 }
 
+// Ensure that the order of dbg.value intrinsics returned by findDbgValues, and
+// their corresponding DPValue representation, are consistent.
+TEST(MetadataTest, OrderingOfDPValues) {
+  LLVMContext C;
+  std::unique_ptr<Module> M = parseIR(C, R"(
+    define i16 @f(i16 %a) !dbg !6 {
+      %b = add i16 %a, 1, !dbg !11
+      call void @llvm.dbg.value(metadata i16 %b, metadata !9, metadata !DIExpression()), !dbg !11
+      call void @llvm.dbg.value(metadata i16 %b, metadata !12, metadata !DIExpression()), !dbg !11
+      ret i16 0, !dbg !11
+    }
+    declare void @llvm.dbg.value(metadata, metadata, metadata) #0
+    attributes #0 = { nounwind readnone speculatable willreturn }
+
+    !llvm.dbg.cu = !{!0}
+    !llvm.module.flags = !{!5}
+
+    !0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+    !1 = !DIFile(filename: "t.ll", directory: "/")
+    !2 = !{}
+    !5 = !{i32 2, !"Debug Info Version", i32 3}
+    !6 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
+    !7 = !DISubroutineType(types: !2)
+    !8 = !{!9}
+    !9 = !DILocalVariable(name: "foo", scope: !6, file: !1, line: 1, type: !10)
+    !10 = !DIBasicType(name: "ty16", size: 16, encoding: DW_ATE_unsigned)
+    !11 = !DILocation(line: 1, column: 1, scope: !6)
+    !12 = !DILocalVariable(name: "bar", scope: !6, file: !1, line: 1, type: !10)
+)");
+
+  bool OldDbgValueMode = UseNewDbgInfoFormat;
+  UseNewDbgInfoFormat = true;
+  Instruction &I = *M->getFunction("f")->getEntryBlock().getFirstNonPHI();
+
+  SmallVector<DbgValueInst *, 2> DVIs;
+  SmallVector<DPValue *, 2> DPVs;
+  findDbgValues(DVIs, &I, &DPVs);
+  ASSERT_EQ(DVIs.size(), 2u);
+  ASSERT_EQ(DPVs.size(), 0u);
+
+  // The correct order of dbg.values is given by their use-list, which becomes
+  // the reverse order of creation. Thus the dbg.values should come out as
+  // "bar" and then "foo".
+  DILocalVariable *Var0 = DVIs[0]->getVariable();
+  EXPECT_TRUE(Var0->getName() == "bar");
+  DILocalVariable *Var1 = DVIs[1]->getVariable();
+  EXPECT_TRUE(Var1->getName() == "foo");
+
+  // Now try again, but in DPValue form.
+  DVIs.clear();
+
+  M->convertToNewDbgValues();
+  findDbgValues(DVIs, &I, &DPVs);
+  ASSERT_EQ(DVIs.size(), 0u);
+  ASSERT_EQ(DPVs.size(), 2u);
+
+  Var0 = DPVs[0]->getVariable();
+  EXPECT_TRUE(Var0->getName() == "bar");
+  Var1 = DPVs[1]->getVariable();
+  EXPECT_TRUE(Var1->getName() == "foo");
+
+  M->convertFromNewDbgValues();
+  UseNewDbgInfoFormat = OldDbgValueMode;
+}
+
 TEST(DIBuiler, CreateFile) {
   LLVMContext Ctx;
   std::unique_ptr<Module> M(new Module("MyModule", Ctx));