2 files changed, 23 insertions, 5 deletions
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
index 1c5a244d7c5..96ce3600417 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -246,8 +246,8 @@ bool DwarfExpression::addMachineRegExpression(const TargetRegisterInfo &TRI,
   // a call site parameter expression and if that expression is just a register
   // location, emit it with addBReg and offset 0, because we should emit a DWARF
   // expression representing a value, rather than a location.
-  if (!isMemoryLocation() && !HasComplexExpression &&
-      (!isParameterValue() || isEntryValue())) {
+  if (!isMemoryLocation() && !HasComplexExpression && (!isParameterValue() ||
+                                                       isEntryValue())) {
     for (auto &Reg : DwarfRegs) {
       if (Reg.DwarfRegNo >= 0)
         addReg(Reg.DwarfRegNo, Reg.Comment);
@@ -436,9 +436,6 @@ void DwarfExpression::addExpression(DIExpressionCursor &&ExprCursor,
       break;
     case dwarf::DW_OP_deref:
       assert(!isRegisterLocation());
-      // For more detailed explanation see llvm.org/PR43343.
-      assert(!isParameterValue() && "Parameter entry values should not be "
-                                    "dereferenced due to safety reasons.");
       if (!isMemoryLocation() && ::isMemoryLocation(ExprCursor))
         // Turning this into a memory location description makes the deref
         // implicit.
diff --git a/llvm/lib/CodeGen/TargetInstrInfo.cpp b/llvm/lib/CodeGen/TargetInstrInfo.cpp
index 81238307d3f..2b987dabd24 100644
--- a/llvm/lib/CodeGen/TargetInstrInfo.cpp
+++ b/llvm/lib/CodeGen/TargetInstrInfo.cpp
@@ -1131,6 +1131,27 @@ TargetInstrInfo::describeLoadedValue(const MachineInstr &MI) const {
   } else if (auto DestSrc = isAddImmediate(MI, Offset)) {
     Expr = DIExpression::prepend(Expr, DIExpression::ApplyOffset, Offset);
     return ParamLoadedValue(*DestSrc->Source, Expr);
+  } else if (MI.hasOneMemOperand()) {
+    // Only describe memory which provably does not escape the function. As
+    // described in llvm.org/PR43343, escaped memory may be clobbered by the
+    // callee (or by another thread).
+    const auto &TII = MF->getSubtarget().getInstrInfo();
+    const MachineFrameInfo &MFI = MF->getFrameInfo();
+    const MachineMemOperand *MMO = MI.memoperands()[0];
+    const PseudoSourceValue *PSV = MMO->getPseudoValue();
+
+    // If the address points to "special" memory (e.g. a spill slot), it's
+    // sufficient to check that it isn't aliased by any high-level IR value.
+    if (!PSV || PSV->mayAlias(&MFI))
+      return None;
+
+    const auto &TRI = MF->getSubtarget().getRegisterInfo();
+    const MachineOperand *BaseOp;
+    if (!TII->getMemOperandWithOffset(MI, BaseOp, Offset, TRI))
+      return None;
+
+    Expr = DIExpression::prepend(Expr, DIExpression::DerefAfter, Offset);
+    return ParamLoadedValue(*BaseOp, Expr);
   }
 
   return None;