[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

1 files changed, 10 insertions, 9 deletions

diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index c96606af6bb..d5986a53aa9 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -4102,9 +4102,10 @@ bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &AS) {
 
   // Migrate debug information from the old alloca to the new alloca(s)
   // and the individual partitions.
-  if (DbgDeclareInst *DbgDecl = FindAllocaDbgDeclare(&AI)) {
-    auto *Var = DbgDecl->getVariable();
-    auto *Expr = DbgDecl->getExpression();
+  TinyPtrVector<DbgInfoIntrinsic *> DbgDeclares = FindDbgAddrUses(&AI);
+  if (!DbgDeclares.empty()) {
+    auto *Var = DbgDeclares.front()->getVariable();
+    auto *Expr = DbgDeclares.front()->getExpression();
     DIBuilder DIB(*AI.getModule(), /*AllowUnresolved*/ false);
     uint64_t AllocaSize = DL.getTypeSizeInBits(AI.getAllocatedType());
     for (auto Fragment : Fragments) {
@@ -4136,12 +4137,12 @@ bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &AS) {
             DIExpression::createFragmentExpression(Expr, Start, Size);
       }
 
-      // Remove any existing dbg.declare intrinsic describing the same alloca.
-      if (DbgDeclareInst *OldDDI = FindAllocaDbgDeclare(Fragment.Alloca))
-        OldDDI->eraseFromParent();
+      // Remove any existing intrinsics describing the same alloca.
+      for (DbgInfoIntrinsic *OldDII : FindDbgAddrUses(Fragment.Alloca))
+        OldDII->eraseFromParent();
 
       DIB.insertDeclare(Fragment.Alloca, Var, FragmentExpr,
-                        DbgDecl->getDebugLoc(), &AI);
+                        DbgDeclares.front()->getDebugLoc(), &AI);
     }
   }
   return Changed;
@@ -4258,8 +4259,8 @@ void SROA::deleteDeadInstructions(
 
     if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
       DeletedAllocas.insert(AI);
-      if (DbgDeclareInst *DbgDecl = FindAllocaDbgDeclare(AI))
-        DbgDecl->eraseFromParent();
+      for (DbgInfoIntrinsic *OldDII : FindDbgAddrUses(AI))
+        OldDII->eraseFromParent();
     }
 
     ++NumDeleted;