[DebugInfo] Unify logic to merge DILocations. NFC.

[vsk]

Summary

This makes DILocation::getMergedLocation() do what its comment says it
does when merging locations for an Instruction: set the common inlineAt
scope. This simplifies Instruction::applyMergedLocation() a bit.

Testing: check-llvm, check-clang

[aprantl]

It looks like this will cause DILocation::getMergedLocation() to create new DILocations? When this happens at the MIR level this will cause problems with the textual MIR output because the new locations aren't printed. Should we introduce a flag to disable creation of new metadata?

[vsk]

In D39628#915861, @aprantl wrote:

It looks like this will cause DILocation::getMergedLocation() to create new DILocations? When this happens at the MIR level this will cause problems with the textual MIR output because the new locations aren't printed. Should we introduce a flag to disable creation of new metadata?

getMergedLocation() shouldn't be able to create a new DILocation unless ForInst is-a CallInst, which shouldn't happen at the MIR level. If we added a flag to explicitly disable creation of new metadata, it would be 'true' iff ForInst is not a CallInst. Can I instead add more documentation for the ForInst parameter?

[aprantl]

What about the common-parent-scope-finding logic?

[vsk]

In D39628#916956, @aprantl wrote:

What about the common-parent-scope-finding logic?

Prior to this patch, the common-parent-scope finding logic could only kick in if this is-a CallInst. That behavior is preserved: DILocation::getMergedLocation() only finds a common parent scope when ForInst is-a CallInst.

[aprantl]

Oh.. I overlooked the early exit. Yeah I guess we can do this.

Can I instead add more documentation for the ForInst parameter?

definitely.

[uweigand]

I've run into an internal compiler error that seems caused by this behavior of getMergedLocation: https://bugs.llvm.org/show_bug.cgi?id=36410

include/llvm/IR/DebugInfoMetadata.h

public:
   /// When the locations are the same we can use either location. When they
   /// differ, we need a third location which is distinct from either. If
   /// they have the same file/line but have a different discriminator we
   /// could create a location with a new discriminator. If they are from
   /// different files/lines the location is ambiguous and can't be
   /// represented in a single line entry.  In this case, no location
   /// should be set, unless the merged instruction is a call, which we will
   /// set the merged debug location as line 0 of the nearest common scope
-  /// where 2 locations are inlined from. This only applies to Instruction,
-  /// For MachineInstruction, as it is post-inline, we will treat the call
+  /// where 2 locations are inlined from. This only applies to Instruction;
+  /// for MachineInstruction, as it is post-inline, we will treat the call
   /// instruction the same way as other instructions.
-  ///
-  /// This should only be used by MachineInstruction because call can be
-  /// treated the same as other instructions. Otherwise, use
-  /// \p applyMergedLocation instead.
-  static const DILocation *getMergedLocation(const DILocation *LocA,
-                                             const DILocation *LocB) {
-    if (LocA && LocB && (LocA == LocB || !LocA->canDiscriminate(*LocB)))
-      return LocA;
-    return nullptr;
-  }
+  static const DILocation *
+  getMergedLocation(const DILocation *LocA, const DILocation *LocB,
+                    const Instruction *ForInst = nullptr);
 
   /// Returns the base discriminator for a given encoded discriminator \p D.
   static unsigned getBaseDiscriminatorFromDiscriminator(unsigned D) {
     if ((D & 1) == 0)
       return getUnsignedFromPrefixEncoding(D >> 1);
     else
       return 0;
   }

lib/IR/DebugInfo.cpp

unsigned llvm::getDebugMetadataVersionFromModule(const Module &M) {
   if (auto *Val = mdconst::dyn_extract_or_null<ConstantInt>(
           M.getModuleFlag("Debug Info Version")))
     return Val->getZExtValue();
   return 0;
 }
 
 void Instruction::applyMergedLocation(const DILocation *LocA,
                                       const DILocation *LocB) {
-  if (LocA && LocB && (LocA == LocB || !LocA->canDiscriminate(*LocB))) {
-    setDebugLoc(LocA);
-    return;
-  }
-  if (!LocA || !LocB || !isa<CallInst>(this)) {
-    setDebugLoc(nullptr);
-    return;
-  }
-  SmallPtrSet<DILocation *, 5> InlinedLocationsA;
-  for (DILocation *L = LocA->getInlinedAt(); L; L = L->getInlinedAt())
-    InlinedLocationsA.insert(L);
-  const DILocation *Result = LocB;
-  for (DILocation *L = LocB->getInlinedAt(); L; L = L->getInlinedAt()) {
-    Result = L;
-    if (InlinedLocationsA.count(L))
-      break;
-  }
-  setDebugLoc(DILocation::get(
-      Result->getContext(), 0, 0, Result->getScope(), Result->getInlinedAt()));
+  setDebugLoc(DILocation::getMergedLocation(LocA, LocB, this));
 }
 
 //===----------------------------------------------------------------------===//
 // LLVM C API implementations.
 //===----------------------------------------------------------------------===//
 
 static unsigned map_from_llvmDWARFsourcelanguage(LLVMDWARFSourceLanguage lang) {
   switch (lang) {

lib/IR/DebugInfoMetadata.cpp

 //===- DebugInfoMetadata.cpp - Implement debug info metadata --------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the debug info Metadata classes.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "LLVMContextImpl.h"
 #include "MetadataImpl.h"
+#include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/IR/DIBuilder.h"
 #include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
 
 using namespace llvm;
 
 DILocation::DILocation(LLVMContext &C, StorageType Storage, unsigned Line,
                        unsigned Column, ArrayRef<Metadata *> MDs)
     : MDNode(C, DILocationKind, Storage, MDs) {
   assert((MDs.size() == 1 || MDs.size() == 2) &&
          "Expected a scope and optional inlined-at");
DILocation *DILocation::getImpl(LLVMContext &Context, unsigned Line,
   Ops.push_back(Scope);
   if (InlinedAt)
     Ops.push_back(InlinedAt);
   return storeImpl(new (Ops.size())
                        DILocation(Context, Storage, Line, Column, Ops),
                    Storage, Context.pImpl->DILocations);
 }
 
+const DILocation *
+DILocation::getMergedLocation(const DILocation *LocA, const DILocation *LocB,
+                              const Instruction *ForInst) {
+  if (!LocA || !LocB)
+    return nullptr;
+
+  if (LocA == LocB || !LocA->canDiscriminate(*LocB))
+    return LocA;
+
+  if (!dyn_cast_or_null<CallInst>(ForInst))
+    return nullptr;
+
+  SmallPtrSet<DILocation *, 5> InlinedLocationsA;
+  for (DILocation *L = LocA->getInlinedAt(); L; L = L->getInlinedAt())
+    InlinedLocationsA.insert(L);
+  const DILocation *Result = LocB;
+  for (DILocation *L = LocB->getInlinedAt(); L; L = L->getInlinedAt()) {
+    Result = L;
+    if (InlinedLocationsA.count(L))
+      break;
+  }
+  return DILocation::get(Result->getContext(), 0, 0, Result->getScope(),
+                         Result->getInlinedAt());
+}
+
 DINode::DIFlags DINode::getFlag(StringRef Flag) {
   return StringSwitch<DIFlags>(Flag)
 #define HANDLE_DI_FLAG(ID, NAME) .Case("DIFlag" #NAME, Flag##NAME)
 #include "llvm/IR/DebugInfoFlags.def"
       .Default(DINode::FlagZero);
 }
 
 StringRef DINode::getFlagString(DIFlags Flag) {