[IR] Add llvm.dbg.addr, a control-dependent version of llvm.dbg.declare

Summary:
This implements the design discussed on llvm-dev for better tracking of
variables that live in memory through optimizations:
  http://lists.llvm.org/pipermail/llvm-dev/2017-September/117222.html

This is tracked as PR34136

llvm.dbg.addr is intended to be produced and used in almost precisely
the same way as llvm.dbg.declare is today, with the exception that it is
control-dependent. That means that dbg.addr should always have a
position in the instruction stream, and it will allow passes that
optimize memory operations on local variables to insert llvm.dbg.value
calls to reflect deleted stores. See SourceLevelDebugging.rst for more
details.

The main drawback to generating DBG_VALUE machine instrs is that they
usually cause LLVM to emit a location list for DW_AT_location. The next
step will be to teach DwarfDebug.cpp how to recognize more DBG_VALUE
ranges as not needing a location list, and possibly start setting
DW_AT_start_offset for variables whose lifetimes begin mid-scope.

Reviewers: aprantl, dblaikie, probinson

Subscribers: eraman, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D37768

llvm-svn: 313825

2 files changed, 72 insertions, 63 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index c3251e26340..43b07557e09 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1098,12 +1098,13 @@ static bool PhiHasDebugValue(DILocalVariable *DIVar,
 }
 
 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
-/// that has an associated llvm.dbg.decl intrinsic.
-void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
+/// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
+void llvm::ConvertDebugDeclareToDebugValue(DbgInfoIntrinsic *DII,
                                            StoreInst *SI, DIBuilder &Builder) {
-  auto *DIVar = DDI->getVariable();
+  assert(DII->isAddressOfVariable());
+  auto *DIVar = DII->getVariable();
   assert(DIVar && "Missing variable");
-  auto *DIExpr = DDI->getExpression();
+  auto *DIExpr = DII->getExpression();
   Value *DV = SI->getOperand(0);
 
   // If an argument is zero extended then use argument directly. The ZExt
@@ -1114,7 +1115,7 @@ void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
   if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
     ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
   if (ExtendedArg) {
-    // If this DDI was already describing only a fragment of a variable, ensure
+    // If this DII was already describing only a fragment of a variable, ensure
     // that fragment is appropriately narrowed here.
     // But if a fragment wasn't used, describe the value as the original
     // argument (rather than the zext or sext) so that it remains described even
@@ -1127,23 +1128,23 @@ void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
                                    DIExpr->elements_end() - 3);
       Ops.push_back(dwarf::DW_OP_LLVM_fragment);
       Ops.push_back(FragmentOffset);
-      const DataLayout &DL = DDI->getModule()->getDataLayout();
+      const DataLayout &DL = DII->getModule()->getDataLayout();
       Ops.push_back(DL.getTypeSizeInBits(ExtendedArg->getType()));
       DIExpr = Builder.createExpression(Ops);
     }
     DV = ExtendedArg;
   }
   if (!LdStHasDebugValue(DIVar, DIExpr, SI))
-    Builder.insertDbgValueIntrinsic(DV, DIVar, DIExpr, DDI->getDebugLoc(),
+    Builder.insertDbgValueIntrinsic(DV, DIVar, DIExpr, DII->getDebugLoc(),
                                     SI);
 }
 
 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
-/// that has an associated llvm.dbg.decl intrinsic.
-void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
+/// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
+void llvm::ConvertDebugDeclareToDebugValue(DbgInfoIntrinsic *DII,
                                            LoadInst *LI, DIBuilder &Builder) {
-  auto *DIVar = DDI->getVariable();
-  auto *DIExpr = DDI->getExpression();
+  auto *DIVar = DII->getVariable();
+  auto *DIExpr = DII->getExpression();
   assert(DIVar && "Missing variable");
 
   if (LdStHasDebugValue(DIVar, DIExpr, LI))
@@ -1154,16 +1155,16 @@ void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
   // preferable to keep tracking both the loaded value and the original
   // address in case the alloca can not be elided.
   Instruction *DbgValue = Builder.insertDbgValueIntrinsic(
-      LI, DIVar, DIExpr, DDI->getDebugLoc(), (Instruction *)nullptr);
+      LI, DIVar, DIExpr, DII->getDebugLoc(), (Instruction *)nullptr);
   DbgValue->insertAfter(LI);
 }
 
-/// Inserts a llvm.dbg.value intrinsic after a phi
-/// that has an associated llvm.dbg.decl intrinsic.
-void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
+/// Inserts a llvm.dbg.value intrinsic after a phi that has an associated
+/// llvm.dbg.declare or llvm.dbg.addr intrinsic.
+void llvm::ConvertDebugDeclareToDebugValue(DbgInfoIntrinsic *DII,
                                            PHINode *APN, DIBuilder &Builder) {
-  auto *DIVar = DDI->getVariable();
-  auto *DIExpr = DDI->getExpression();
+  auto *DIVar = DII->getVariable();
+  auto *DIExpr = DII->getExpression();
   assert(DIVar && "Missing variable");
 
   if (PhiHasDebugValue(DIVar, DIExpr, APN))
@@ -1176,7 +1177,7 @@ void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
   // insertion point.
   // FIXME: Insert dbg.value markers in the successors when appropriate.
   if (InsertionPt != BB->end())
-    Builder.insertDbgValueIntrinsic(APN, DIVar, DIExpr, DDI->getDebugLoc(),
+    Builder.insertDbgValueIntrinsic(APN, DIVar, DIExpr, DII->getDebugLoc(),
                                     &*InsertionPt);
 }
 
@@ -1231,16 +1232,25 @@ bool llvm::LowerDbgDeclare(Function &F) {
   return true;
 }
 
-/// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
-/// alloca 'V', if any.
-DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
-  if (auto *L = LocalAsMetadata::getIfExists(V))
-    if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
-      for (User *U : MDV->users())
-        if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
-          return DDI;
+/// Finds all intrinsics declaring local variables as living in the memory that
+/// 'V' points to. This may include a mix of dbg.declare and
+/// dbg.addr intrinsics.
+TinyPtrVector<DbgInfoIntrinsic *> llvm::FindDbgAddrUses(Value *V) {
+  auto *L = LocalAsMetadata::getIfExists(V);
+  if (!L)
+    return {};
+  auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L);
+  if (!MDV)
+    return {};
+
+  TinyPtrVector<DbgInfoIntrinsic *> Declares;
+  for (User *U : MDV->users()) {
+    if (auto *DII = dyn_cast<DbgInfoIntrinsic>(U))
+      if (DII->isAddressOfVariable())
+        Declares.push_back(DII);
+  }
 
-  return nullptr;
+  return Declares;
 }
 
 void llvm::findDbgValues(SmallVectorImpl<DbgValueInst *> &DbgValues, Value *V) {
@@ -1251,23 +1261,22 @@ void llvm::findDbgValues(SmallVectorImpl<DbgValueInst *> &DbgValues, Value *V) {
           DbgValues.push_back(DVI);
 }
 
-
 bool llvm::replaceDbgDeclare(Value *Address, Value *NewAddress,
                              Instruction *InsertBefore, DIBuilder &Builder,
                              bool Deref, int Offset) {
-  DbgDeclareInst *DDI = FindAllocaDbgDeclare(Address);
-  if (!DDI)
-    return false;
-  DebugLoc Loc = DDI->getDebugLoc();
-  auto *DIVar = DDI->getVariable();
-  auto *DIExpr = DDI->getExpression();
-  assert(DIVar && "Missing variable");
-  DIExpr = DIExpression::prepend(DIExpr, Deref, Offset);
-  // Insert llvm.dbg.declare immediately after the original alloca, and remove
-  // old llvm.dbg.declare.
-  Builder.insertDeclare(NewAddress, DIVar, DIExpr, Loc, InsertBefore);
-  DDI->eraseFromParent();
-  return true;
+  auto DbgAddrs = FindDbgAddrUses(Address);
+  for (DbgInfoIntrinsic *DII : DbgAddrs) {
+    DebugLoc Loc = DII->getDebugLoc();
+    auto *DIVar = DII->getVariable();
+    auto *DIExpr = DII->getExpression();
+    assert(DIVar && "Missing variable");
+    DIExpr = DIExpression::prepend(DIExpr, Deref, Offset);
+    // Insert llvm.dbg.declare immediately after the original alloca, and remove
+    // old llvm.dbg.declare.
+    Builder.insertDeclare(NewAddress, DIVar, DIExpr, Loc, InsertBefore);
+    DII->eraseFromParent();
+  }
+  return !DbgAddrs.empty();
 }
 
 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
diff --git a/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
index ac28f590b01..e2ba5c4cfbb 100644
--- a/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
+++ b/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -103,7 +103,7 @@ struct AllocaInfo {
   bool OnlyUsedInOneBlock;
 
   Value *AllocaPointerVal;
-  DbgDeclareInst *DbgDeclare;
+  TinyPtrVector<DbgInfoIntrinsic*> DbgDeclares;
 
   void clear() {
     DefiningBlocks.clear();
@@ -112,7 +112,7 @@ struct AllocaInfo {
     OnlyBlock = nullptr;
     OnlyUsedInOneBlock = true;
     AllocaPointerVal = nullptr;
-    DbgDeclare = nullptr;
+    DbgDeclares.clear();
   }
 
   /// Scan the uses of the specified alloca, filling in the AllocaInfo used
@@ -147,7 +147,7 @@ struct AllocaInfo {
       }
     }
 
-    DbgDeclare = FindAllocaDbgDeclare(AI);
+    DbgDeclares = FindDbgAddrUses(AI);
   }
 };
 
@@ -245,7 +245,7 @@ struct PromoteMem2Reg {
   /// For each alloca, we keep track of the dbg.declare intrinsic that
   /// describes it, if any, so that we can convert it to a dbg.value
   /// intrinsic if the alloca gets promoted.
-  SmallVector<DbgDeclareInst *, 8> AllocaDbgDeclares;
+  SmallVector<TinyPtrVector<DbgInfoIntrinsic *>, 8> AllocaDbgDeclares;
 
   /// The set of basic blocks the renamer has already visited.
   ///
@@ -409,11 +409,11 @@ static bool rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info,
 
   // Record debuginfo for the store and remove the declaration's
   // debuginfo.
-  if (DbgDeclareInst *DDI = Info.DbgDeclare) {
+  for (DbgInfoIntrinsic *DII : Info.DbgDeclares) {
     DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
-    ConvertDebugDeclareToDebugValue(DDI, Info.OnlyStore, DIB);
-    DDI->eraseFromParent();
-    LBI.deleteValue(DDI);
+    ConvertDebugDeclareToDebugValue(DII, Info.OnlyStore, DIB);
+    DII->eraseFromParent();
+    LBI.deleteValue(DII);
   }
   // Remove the (now dead) store and alloca.
   Info.OnlyStore->eraseFromParent();
@@ -505,9 +505,9 @@ static bool promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info,
   while (!AI->use_empty()) {
     StoreInst *SI = cast<StoreInst>(AI->user_back());
     // Record debuginfo for the store before removing it.
-    if (DbgDeclareInst *DDI = Info.DbgDeclare) {
+    for (DbgInfoIntrinsic *DII : Info.DbgDeclares) {
       DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
-      ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
+      ConvertDebugDeclareToDebugValue(DII, SI, DIB);
     }
     SI->eraseFromParent();
     LBI.deleteValue(SI);
@@ -517,9 +517,9 @@ static bool promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info,
   LBI.deleteValue(AI);
 
   // The alloca's debuginfo can be removed as well.
-  if (DbgDeclareInst *DDI = Info.DbgDeclare) {
-    DDI->eraseFromParent();
-    LBI.deleteValue(DDI);
+  for (DbgInfoIntrinsic *DII : Info.DbgDeclares) {
+    DII->eraseFromParent();
+    LBI.deleteValue(DII);
   }
 
   ++NumLocalPromoted;
@@ -587,8 +587,8 @@ void PromoteMem2Reg::run() {
     }
 
     // Remember the dbg.declare intrinsic describing this alloca, if any.
-    if (Info.DbgDeclare)
-      AllocaDbgDeclares[AllocaNum] = Info.DbgDeclare;
+    if (!Info.DbgDeclares.empty())
+      AllocaDbgDeclares[AllocaNum] = Info.DbgDeclares;
 
     // Keep the reverse mapping of the 'Allocas' array for the rename pass.
     AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
@@ -666,9 +666,9 @@ void PromoteMem2Reg::run() {
   }
 
   // Remove alloca's dbg.declare instrinsics from the function.
-  for (DbgDeclareInst *DDI : AllocaDbgDeclares)
-    if (DDI)
-      DDI->eraseFromParent();
+  for (auto &Declares : AllocaDbgDeclares)
+    for (auto *DII : Declares)
+      DII->eraseFromParent();
 
   // Loop over all of the PHI nodes and see if there are any that we can get
   // rid of because they merge all of the same incoming values.  This can
@@ -895,8 +895,8 @@ NextIteration:
 
         // The currently active variable for this block is now the PHI.
         IncomingVals[AllocaNo] = APN;
-        if (DbgDeclareInst *DDI = AllocaDbgDeclares[AllocaNo])
-          ConvertDebugDeclareToDebugValue(DDI, APN, DIB);
+        for (DbgInfoIntrinsic *DII : AllocaDbgDeclares[AllocaNo])
+          ConvertDebugDeclareToDebugValue(DII, APN, DIB);
 
         // Get the next phi node.
         ++PNI;
@@ -952,8 +952,8 @@ NextIteration:
       // what value were we writing?
       IncomingVals[ai->second] = SI->getOperand(0);
       // Record debuginfo for the store before removing it.
-      if (DbgDeclareInst *DDI = AllocaDbgDeclares[ai->second])
-        ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
+      for (DbgInfoIntrinsic *DII : AllocaDbgDeclares[ai->second])
+        ConvertDebugDeclareToDebugValue(DII, SI, DIB);
       BB->getInstList().erase(SI);
     }
   }