3 files changed, 45 insertions, 11 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 27ac489b35b..735ac67ebfc 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5571,8 +5571,26 @@ bool SelectionDAGBuilder::EmitFuncArgumentDbgValue(
       = [&](ArrayRef<std::pair<unsigned, unsigned>> SplitRegs) {
       unsigned Offset = 0;
       for (auto RegAndSize : SplitRegs) {
+        // If the expression is already a fragment, the current register
+        // offset+size might extend beyond the fragment. In this case, only
+        // the register bits that are inside the fragment are relevant.
+        int RegFragmentSizeInBits = RegAndSize.second;
+        if (auto ExprFragmentInfo = Expr->getFragmentInfo()) {
+          uint64_t ExprFragmentSizeInBits = ExprFragmentInfo->SizeInBits;
+          // The register is entirely outside the expression fragment,
+          // so is irrelevant for debug info.
+          if (Offset >= ExprFragmentSizeInBits)
+            break;
+          // The register is partially outside the expression fragment, only
+          // the low bits within the fragment are relevant for debug info.
+          if (Offset + RegFragmentSizeInBits > ExprFragmentSizeInBits) {
+            RegFragmentSizeInBits = ExprFragmentSizeInBits - Offset;
+          }
+        }
+
         auto FragmentExpr = DIExpression::createFragmentExpression(
-          Expr, Offset, RegAndSize.second);
+            Expr, Offset, RegFragmentSizeInBits);
+        Offset += RegAndSize.second;
         // If a valid fragment expression cannot be created, the variable's
         // correct value cannot be determined and so it is set as Undef.
         if (!FragmentExpr) {
@@ -5585,7 +5603,6 @@ bool SelectionDAGBuilder::EmitFuncArgumentDbgValue(
         FuncInfo.ArgDbgValues.push_back(
           BuildMI(MF, DL, TII->get(TargetOpcode::DBG_VALUE), false,
                   RegAndSize.first, Variable, *FragmentExpr));
-        Offset += RegAndSize.second;
       }
     };
 
diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index 9b42a5a0e1b..ed35a7c5548 100644
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -1196,13 +1196,18 @@ bool DIExpression::isConstant() const {
   return true;
 }
 
+DIExpression::ExtOps DIExpression::getExtOps(unsigned FromSize, unsigned ToSize,
+                                             bool Signed) {
+  dwarf::TypeKind TK = Signed ? dwarf::DW_ATE_signed : dwarf::DW_ATE_unsigned;
+  DIExpression::ExtOps Ops{{dwarf::DW_OP_LLVM_convert, FromSize, TK,
+                            dwarf::DW_OP_LLVM_convert, ToSize, TK}};
+  return Ops;
+}
+
 DIExpression *DIExpression::appendExt(const DIExpression *Expr,
                                       unsigned FromSize, unsigned ToSize,
                                       bool Signed) {
-  dwarf::TypeKind TK = Signed ? dwarf::DW_ATE_signed : dwarf::DW_ATE_unsigned;
-  uint64_t Ops[] = {dwarf::DW_OP_LLVM_convert, FromSize, TK,
-                    dwarf::DW_OP_LLVM_convert, ToSize,   TK};
-  return appendToStack(Expr, Ops);
+  return appendToStack(Expr, getExtOps(FromSize, ToSize, Signed));
 }
 
 DIGlobalVariableExpression *
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index d5690a04f53..b2d511c7c9a 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1676,9 +1676,8 @@ DIExpression *llvm::salvageDebugInfoImpl(Instruction &I,
   };
 
   // initializer-list helper for applying operators to the source DIExpression.
-  auto applyOps =
-      [&](std::initializer_list<uint64_t> Opcodes) -> DIExpression * {
-    SmallVector<uint64_t, 8> Ops(Opcodes);
+  auto applyOps = [&](ArrayRef<uint64_t> Opcodes) -> DIExpression * {
+    SmallVector<uint64_t, 8> Ops(Opcodes.begin(), Opcodes.end());
     return doSalvage(Ops);
   };
 
@@ -1686,8 +1685,21 @@ DIExpression *llvm::salvageDebugInfoImpl(Instruction &I,
     // No-op casts and zexts are irrelevant for debug info.
     if (CI->isNoopCast(DL) || isa<ZExtInst>(&I))
       return SrcDIExpr;
-    return nullptr;
-  } else if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
+
+    Type *Type = CI->getType();
+    // Casts other than Trunc or SExt to scalar types cannot be salvaged.
+    if (Type->isVectorTy() || (!isa<TruncInst>(&I) && !isa<SExtInst>(&I)))
+      return nullptr;
+
+    Value *FromValue = CI->getOperand(0);
+    unsigned FromTypeBitSize = FromValue->getType()->getScalarSizeInBits();
+    unsigned ToTypeBitSize = Type->getScalarSizeInBits();
+
+    return applyOps(DIExpression::getExtOps(FromTypeBitSize, ToTypeBitSize,
+                                            isa<SExtInst>(&I)));
+  }
+
+  if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
     unsigned BitWidth =
         M.getDataLayout().getIndexSizeInBits(GEP->getPointerAddressSpace());
     // Rewrite a constant GEP into a DIExpression.