[Utils] Salvage debug info in recursive inst deletion

In stage2 -O3 builds of llc, this results in a 0.3% increase in the
number of variables with locations, and a 0.2% increase in the number of
unique source variables overall.

The size of the .debug_loc section of the llc dsym increases by 0.5%.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@326621 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 61 insertions, 0 deletions

diff --git a/unittests/Transforms/Utils/Local.cpp b/unittests/Transforms/Utils/Local.cpp
index 2343c46057e..679a7a3c3ff 100644
--- a/unittests/Transforms/Utils/Local.cpp
+++ b/unittests/Transforms/Utils/Local.cpp
@@ -331,3 +331,64 @@ TEST(Local, ConstantFoldTerminator) {
   runWithDomTree(*M, "indirectbr_repeated", CFAllTerminators);
   runWithDomTree(*M, "indirectbr_unreachable", CFAllTerminators);
 }
+
+TEST(Local, SalvageDebugValuesInRecursiveInstDeletion) {
+  LLVMContext C;
+
+  std::unique_ptr<Module> M = parseIR(C,
+                                      R"(
+      define void @f() !dbg !8 {
+      entry:
+        %x = add i32 0, 1
+        %y = add i32 %x, 2
+        call void @llvm.dbg.value(metadata i32 %x, metadata !11, metadata !DIExpression()), !dbg !13
+        call void @llvm.dbg.value(metadata i32 %y, metadata !11, metadata !DIExpression()), !dbg !13
+        ret void, !dbg !14
+      }
+      declare void @llvm.dbg.value(metadata, metadata, metadata)
+      !llvm.dbg.cu = !{!0}
+      !llvm.module.flags = !{!3, !4}
+      !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 6.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+      !1 = !DIFile(filename: "t2.c", directory: "foo")
+      !2 = !{}
+      !3 = !{i32 2, !"Dwarf Version", i32 4}
+      !4 = !{i32 2, !"Debug Info Version", i32 3}
+      !8 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 1, type: !9, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: false, unit: !0, variables: !2)
+      !9 = !DISubroutineType(types: !10)
+      !10 = !{null}
+      !11 = !DILocalVariable(name: "x", scope: !8, file: !1, line: 2, type: !12)
+      !12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+      !13 = !DILocation(line: 2, column: 7, scope: !8)
+      !14 = !DILocation(line: 3, column: 1, scope: !8)
+      )");
+  auto *GV = M->getNamedValue("f");
+  ASSERT_TRUE(GV);
+  auto *F = dyn_cast<Function>(GV);
+  ASSERT_TRUE(F);
+  Instruction *Inst = &F->front().front();
+  Inst = Inst->getNextNode();
+  ASSERT_TRUE(Inst);
+  bool Deleted = RecursivelyDeleteTriviallyDeadInstructions(Inst);
+  ASSERT_TRUE(Deleted);
+
+  // The debug values should have been salvaged.
+  bool FoundX = false;
+  bool FoundY = false;
+  uint64_t X_expr[] = {dwarf::DW_OP_plus_uconst, 1, dwarf::DW_OP_stack_value};
+  uint64_t Y_expr[] = {dwarf::DW_OP_plus_uconst, 1, dwarf::DW_OP_plus_uconst, 2,
+                       dwarf::DW_OP_stack_value};
+  for (const Instruction &I : F->front()) {
+    auto DI = dyn_cast<DbgValueInst>(&I);
+    if (!DI)
+      continue;
+    EXPECT_EQ(DI->getVariable()->getName(), "x");
+    ASSERT_TRUE(cast<ConstantInt>(DI->getValue())->isZero());
+    ArrayRef<uint64_t> ExprElts = DI->getExpression()->getElements();
+    if (ExprElts.equals(X_expr))
+      FoundX = true;
+    else if (ExprElts.equals(Y_expr))
+      FoundY = true;
+  }
+  ASSERT_TRUE(FoundX);
+  ASSERT_TRUE(FoundY);
+}