[llvm] 12ece76 - [DebugInfo] Replace UndefValue with PoisonValue in AssignmentTrackingAnalysis

[via llvm-commits]

Author: OCHyams
Date: 2023-01-12T09:51:45Z
New Revision: 12ece76815ab330f8f33707efd7c93735dd9c178

URL: https://github.com/llvm/llvm-project/commit/12ece76815ab330f8f33707efd7c93735dd9c178
DIFF: https://github.com/llvm/llvm-project/commit/12ece76815ab330f8f33707efd7c93735dd9c178.diff

LOG: [DebugInfo] Replace UndefValue with PoisonValue in AssignmentTrackingAnalysis

This helps towards the effort to remove UndefValue from LLVM.

Related to https://discourse.llvm.org/t/auto-undef-debug-uses-of-a-deleted-value

Reviewed By: scott.linder

Differential Revision: https://reviews.llvm.org/D140906

Added: 
    

Modified: 
    llvm/docs/AssignmentTracking.md
    llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/docs/AssignmentTracking.md b/llvm/docs/AssignmentTracking.md
index 4f07f2d80a5e..969874039320 100644
--- a/llvm/docs/AssignmentTracking.md
+++ b/llvm/docs/AssignmentTracking.md
@@ -63,9 +63,11 @@ void @llvm.dbg.assign(Value *Value,
 
 The first three parameters look and behave like an `llvm.dbg.value`. `ID` is a
 reference to a store (see next section). `Address` is the destination address
-of the store and it is modified by `AddressExpression`. LLVM currently encodes
-variable fragment information in `DIExpression`s, so as an implementation quirk
-the `FragmentInfo` for `Variable` is contained within `ValueExpression` only.
+of the store and it is modified by `AddressExpression`. An empty/undef/poison
+address means the address component has been killed (the memory address is no
+longer a valid location). LLVM currently encodes variable fragment information
+in `DIExpression`s, so as an implementation quirk the `FragmentInfo` for
+`Variable` is contained within `ValueExpression` only.
 
 The formal LLVM-IR signature is:
 ```

diff  --git a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
index bf421a4054c0..ba51c3bedcf7 100644
--- a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
+++ b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
@@ -1239,10 +1239,8 @@ void AssignmentTrackingLowering::emitDbgValue(
   DILocation *DL = Source->getDebugLoc();
   auto Emit = [this, Source, After, DL](Value *Val, DIExpression *Expr) {
     assert(Expr);
-    // It's possible that getVariableLocationOp(0) is null. Occurs in
-    // llvm/test/DebugInfo/Generic/2010-05-03-OriginDIE.ll Treat it as undef.
     if (!Val)
-      Val = UndefValue::get(Type::getInt1Ty(Source->getContext()));
+      Val = PoisonValue::get(Type::getInt1Ty(Source->getContext()));
 
     // Find a suitable insert point.
     Instruction *InsertBefore = After->getNextNode();
@@ -1289,16 +1287,13 @@ void AssignmentTrackingLowering::emitDbgValue(
   if (Kind == LocKind::Val) {
     /// Get the value component, converting to Undef if it is variadic.
     Value *Val =
-        Source->hasArgList()
-            ? UndefValue::get(Source->getVariableLocationOp(0)->getType())
-            : Source->getVariableLocationOp(0);
+        Source->hasArgList() ? nullptr : Source->getVariableLocationOp(0);
     Emit(Val, Source->getExpression());
     return;
   }
 
   if (Kind == LocKind::None) {
-    Value *Val = UndefValue::get(Source->getVariableLocationOp(0)->getType());
-    Emit(Val, Source->getExpression());
+    Emit(nullptr, Source->getExpression());
     return;
   }
 }
@@ -2111,13 +2106,11 @@ bool AssignmentTrackingLowering::emitPromotedVarLocs(
         continue;
       // Wrapper to get a single value (or undef) from DVI.
       auto GetValue = [DVI]() -> Value * {
-        // Conditions for undef: Any operand undef, zero operands or single
-        // operand is nullptr. We also can't handle variadic DIExpressions yet.
-        // Some of those conditions don't have a type we can pick for
-        // undef. Use i32.
+        // We can't handle variadic DIExpressions yet so treat those as
+        // kill locations.
         if (DVI->isKillLocation() || DVI->getValue() == nullptr ||
             DVI->hasArgList())
-          return UndefValue::get(Type::getInt32Ty(DVI->getContext()));
+          return PoisonValue::get(Type::getInt32Ty(DVI->getContext()));
         return DVI->getValue();
       };
       Instruction *InsertBefore = I.getNextNode();