[CodeGen][DebugInfo] Append OP_deref when converting an EntryValue dbg.declare

When we convert an EntryValue dbg.declare into an entry of the MF side table, we
currently copy its DIExpression as is, and rely on subsequent layers to "know"
that this expression is implicitly indirect. This is bad because it adds an
implicit assumption to the IR representation, and requires subsequent layers to
know about this assumption. This also limits the reusability of this table:
what if, in the future, we want to use this table for dbg.values?

This patch changes existing behavior so that the entities converting
dbg_declares explicitly add an OP_deref when converting EntryValue dbg.declares.

Differential Revision: https://reviews.llvm.org/D158437

Author: felipepiovezan

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -1565,7 +1565,7 @@ void DwarfDebug::collectVariableInfoFromMFTable(
     if (VI.inStackSlot())
       RegVar->initializeMMI(VI.Expr, VI.getStackSlot());
     else {
-      MachineLocation MLoc(VI.getEntryValueRegister(), /*IsIndirect*/ true);
+      MachineLocation MLoc(VI.getEntryValueRegister(), /*IsIndirect*/ false);
       auto LocEntry = DbgValueLocEntry(MLoc);
       RegVar->initializeDbgValue(DbgValueLoc(VI.Expr, LocEntry));
     }

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

@@ -1943,6 +1943,8 @@ bool IRTranslator::translateIfEntryValueArgument(
   if (!PhysReg)
     return false;
 
+  // Append an op deref to account for the fact that this is a dbg_declare.
+  Expr = DIExpression::append(Expr, dwarf::DW_OP_deref);
   MF->setVariableDbgInfo(DebugInst.getVariable(), Expr, *PhysReg,
                          DebugInst.getDebugLoc());
   return true;

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -1357,6 +1357,8 @@ static bool processIfEntryValueDbgDeclare(FunctionLoweringInfo &FuncInfo,
   // Find the corresponding livein physical register to this argument.
   for (auto [PhysReg, VirtReg] : FuncInfo.RegInfo->liveins())
     if (VirtReg == ArgVReg) {
+      // Append an op deref to account for the fact that this is a dbg_declare.
+      Expr = DIExpression::append(Expr, dwarf::DW_OP_deref);
       FuncInfo.MF->setVariableDbgInfo(Var, Expr, PhysReg, DbgLoc);
       LLVM_DEBUG(dbgs() << "processDbgDeclare: setVariableDbgInfo Var=" << *Var
                         << ", Expr=" << *Expr << ",  MCRegister=" << PhysReg

llvm/test/CodeGen/AArch64/dbg-declare-swift-async.ll

@@ -3,11 +3,11 @@
 ; RUN: llc -O0 -fast-isel=false -global-isel=false -stop-after=finalize-isel %s -o - | FileCheck %s
 
 ; CHECK: void @foo
-; CHECK-NEXT: dbg.declare(metadata {{.*}}, metadata ![[VAR:.*]], metadata ![[EXPR:.*]]), !dbg ![[LOC:.*]]
+; CHECK-NEXT: dbg.declare(metadata {{.*}}, metadata ![[VAR:.*]], metadata !DIExpression([[EXPR:.*]])), !dbg ![[LOC:.*]]
 ; CHECK: entry_values:
-; CHECK-NEXT: entry-value-register: '$x22', debug-info-variable: '![[VAR]]', debug-info-expression: '![[EXPR]]',
+; CHECK-NEXT: entry-value-register: '$x22', debug-info-variable: '![[VAR]]', debug-info-expression: '!DIExpression([[EXPR]], DW_OP_deref)',
 ; CHECK-NEXT:   debug-info-location: '![[LOC]]
-; CHECK-NEXT: entry-value-register: '$x22', debug-info-variable: '![[VAR]]', debug-info-expression: '![[EXPR]]'
+; CHECK-NEXT: entry-value-register: '$x22', debug-info-variable: '![[VAR]]', debug-info-expression: '!DIExpression([[EXPR]], DW_OP_deref)'
 ; CHECK-NEXT:   debug-info-location: '![[LOC]]
 
 ; CHECK-NOT: DBG_VALUE

llvm/test/DebugInfo/AArch64/dbg-entry-value-swiftasync.mir

@@ -36,7 +36,7 @@ stack:
   - { id: 0, name: '', type: spill-slot, offset: -16, size: 8, alignment: 16,
       stack-id: default, callee-saved-register: '$lr', callee-saved-restored: true }
 entry_values:
-  - { entry-value-register: '$x22', debug-info-variable: '!10', debug-info-expression: '!DIExpression(DW_OP_LLVM_entry_value, 1)',
+  - { entry-value-register: '$x22', debug-info-variable: '!10', debug-info-expression: '!DIExpression(DW_OP_LLVM_entry_value, 1, DW_OP_deref)',
       debug-info-location: '!12' }
 body:             |
   bb.0 (%ir-block.0):