ValueMapper: Treat LocalAsMetadata more like function-local Values

This is a partial re-commit -- maybe more of a re-implementation -- of
r265631 (reverted in r265637).

This makes RF_IgnoreMissingLocals behave (almost) consistently between
the Value and the Metadata hierarchy.  In particular:

  - MapValue returns nullptr or "metadata !{}" for missing locals in
    MetadataAsValue/LocalAsMetadata bridging paris, depending on
    the RF_IgnoreMissingLocals flag.

  - MapValue doesn't memoize LocalAsMetadata-related results.

  - MapMetadata no longer deals with LocalAsMetadata or
    RF_IgnoreMissingLocals at all.  (This wasn't in r265631 at all, but
    I realized during testing it would make the patch simpler with no
    loss of generality.)

r265631 went too far, making both functions universally ignore
RF_IgnoreMissingLocals.  This broke building (e.g.) compiler-rt.
Reassociate (and possibly other passes) don't currently maintain
dominates-use invariants for metadata operands, resulting in IR like
this:

    define void @foo(i32 %arg) {
      call void @llvm.some.intrinsic(metadata i32 %x)
      %x = add i32 1, i32 %arg
    }

If the inliner chooses to inline @foo into another function, then
RemapInstruction will call `MapValue(metadata i32 %x)` and assert that
the return is not nullptr.

I've filed PR27273 to add a Verifier check and fix the underlying
problem in the optimization passes.

As a workaround, return `!{}` instead of nullptr for unmapped
LocalAsMetadata when RF_IgnoreMissingLocals is unset.  Otherwise, match
the behaviour of r265631.

Original commit message:

    ValueMapper: Make LocalAsMetadata match function-local Values

    Start treating LocalAsMetadata similarly to function-local members of
    the Value hierarchy in MapValue and MapMetadata.

      - Don't memoize them.
      - Return nullptr if they are missing.

    This also cleans up ConstantAsMetadata to stop listening to the
    RF_IgnoreMissingLocals flag.

llvm-svn: 265759

1 files changed, 95 insertions, 0 deletions

diff --git a/llvm/unittests/Transforms/Utils/ValueMapperTest.cpp b/llvm/unittests/Transforms/Utils/ValueMapperTest.cpp
index 222f2a2e863..151f76da9cb 100644
--- a/llvm/unittests/Transforms/Utils/ValueMapperTest.cpp
+++ b/llvm/unittests/Transforms/Utils/ValueMapperTest.cpp
@@ -139,4 +139,99 @@ TEST(ValueMapperTest, MapMetadataNullMapGlobalWithIgnoreMissingLocals) {
   EXPECT_EQ(nullptr, MapValue(F.get(), VM, Flags));
 }
 
+TEST(ValueMapperTest, MapMetadataConstantAsMetadata) {
+  LLVMContext C;
+  FunctionType *FTy =
+      FunctionType::get(Type::getVoidTy(C), Type::getInt8Ty(C), false);
+  std::unique_ptr<Function> F(
+      Function::Create(FTy, GlobalValue::ExternalLinkage, "F"));
+
+  auto *CAM = ConstantAsMetadata::get(F.get());
+  {
+    ValueToValueMapTy VM;
+    EXPECT_EQ(CAM, MapMetadata(CAM, VM));
+    EXPECT_TRUE(VM.MD().count(CAM));
+    VM.MD().erase(CAM);
+    EXPECT_EQ(CAM, MapMetadata(CAM, VM, RF_IgnoreMissingLocals));
+    EXPECT_TRUE(VM.MD().count(CAM));
+
+    auto *N = MDTuple::get(C, None);
+    VM.MD()[CAM].reset(N);
+    EXPECT_EQ(N, MapMetadata(CAM, VM));
+    EXPECT_EQ(N, MapMetadata(CAM, VM, RF_IgnoreMissingLocals));
+  }
+
+  std::unique_ptr<Function> F2(
+      Function::Create(FTy, GlobalValue::ExternalLinkage, "F2"));
+  ValueToValueMapTy VM;
+  VM[F.get()] = F2.get();
+  auto *F2MD = MapMetadata(CAM, VM);
+  EXPECT_TRUE(VM.MD().count(CAM));
+  EXPECT_TRUE(F2MD);
+  EXPECT_EQ(F2.get(), cast<ConstantAsMetadata>(F2MD)->getValue());
+}
+
+#ifdef GTEST_HAS_DEATH_TEST
+#ifndef NDEBUG
+TEST(ValueMapperTest, MapMetadataLocalAsMetadata) {
+  LLVMContext C;
+  FunctionType *FTy =
+      FunctionType::get(Type::getVoidTy(C), Type::getInt8Ty(C), false);
+  std::unique_ptr<Function> F(
+      Function::Create(FTy, GlobalValue::ExternalLinkage, "F"));
+  Argument &A = *F->arg_begin();
+
+  // MapMetadata doesn't support LocalAsMetadata.  The only valid container for
+  // LocalAsMetadata is a MetadataAsValue instance, so use it directly.
+  auto *LAM = LocalAsMetadata::get(&A);
+  ValueToValueMapTy VM;
+  EXPECT_DEATH(MapMetadata(LAM, VM), "Unexpected local metadata");
+  EXPECT_DEATH(MapMetadata(LAM, VM, RF_IgnoreMissingLocals),
+               "Unexpected local metadata");
+}
+#endif
+#endif
+
+TEST(ValueMapperTest, MapValueLocalAsMetadata) {
+  LLVMContext C;
+  FunctionType *FTy =
+      FunctionType::get(Type::getVoidTy(C), Type::getInt8Ty(C), false);
+  std::unique_ptr<Function> F(
+      Function::Create(FTy, GlobalValue::ExternalLinkage, "F"));
+  Argument &A = *F->arg_begin();
+
+  auto *LAM = LocalAsMetadata::get(&A);
+  auto *MAV = MetadataAsValue::get(C, LAM);
+
+  // The principled answer to a LocalAsMetadata of an unmapped SSA value would
+  // be to return nullptr (regardless of RF_IgnoreMissingLocals).
+  //
+  // However, algorithms that use RemapInstruction assume that each instruction
+  // only references SSA values from previous instructions.  Arguments of
+  // such as "metadata i32 %x" don't currently successfully maintain that
+  // property.  To keep RemapInstruction from crashing we need a non-null
+  // return here, but we also shouldn't reference the unmapped local.  Use
+  // "metadata !{}".
+  auto *N0 = MDTuple::get(C, None);
+  auto *N0AV = MetadataAsValue::get(C, N0);
+  ValueToValueMapTy VM;
+  EXPECT_EQ(N0AV, MapValue(MAV, VM));
+  EXPECT_EQ(nullptr, MapValue(MAV, VM, RF_IgnoreMissingLocals));
+  EXPECT_FALSE(VM.count(MAV));
+  EXPECT_FALSE(VM.count(&A));
+  EXPECT_EQ(None, VM.getMappedMD(LAM));
+
+  VM[MAV] = MAV;
+  EXPECT_EQ(MAV, MapValue(MAV, VM));
+  EXPECT_EQ(MAV, MapValue(MAV, VM, RF_IgnoreMissingLocals));
+  EXPECT_TRUE(VM.count(MAV));
+  EXPECT_FALSE(VM.count(&A));
+
+  VM[MAV] = &A;
+  EXPECT_EQ(&A, MapValue(MAV, VM));
+  EXPECT_EQ(&A, MapValue(MAV, VM, RF_IgnoreMissingLocals));
+  EXPECT_TRUE(VM.count(MAV));
+  EXPECT_FALSE(VM.count(&A));
+}
+
 } // end namespace