[SelectionDAG][DebugInfo] Handle entry_value dbg.value DIExprs earlier

When SelectiondDAG converts dbg.value intrinsics, it first ensures we have
already generated code for the value operator of the intrinsic. The rationale
being that if we haven't had the need to generate code for this value, it won't
be a debug value that causes the generation.

For example, if the first use the physical register of an argument is a
dbg.value, we are going to hit this code path.  However, this is irrelevant for
entry value expressions: by definition we are not interested in the _current_
value of the physical register, but rather on its value at the start of the
function. To deal with this, this patch changes lowering to handle this case as
early as possible.

Differential Revision: https://reviews.llvm.org/D158649

(cherry picked from commit 35f4ef1)

Author: felipepiovezan

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -5845,26 +5845,6 @@ bool SelectionDAGBuilder::EmitFuncArgumentDbgValue(
   if (!Op)
     return false;
 
-  // If the expression refers to the entry value of an Argument, use the
-  // corresponding livein physical register. As per the Verifier, this is only
-  // allowed for swiftasync Arguments.
-  if (Op->isReg() && Expr->isEntryValue()) {
-    assert(Arg->hasAttribute(Attribute::AttrKind::SwiftAsync));
-    auto OpReg = Op->getReg();
-    for (auto [PhysReg, VirtReg] : FuncInfo.RegInfo->liveins())
-      if (OpReg == VirtReg || OpReg == PhysReg) {
-        SDDbgValue *SDV = DAG.getVRegDbgValue(
-            Variable, Expr, PhysReg,
-            Kind != FuncArgumentDbgValueKind::Value /*is indirect*/, DL,
-            SDNodeOrder);
-        DAG.AddDbgValue(SDV, false /*treat as dbg.declare byval parameter*/);
-        return true;
-      }
-    LLVM_DEBUG(dbgs() << "Dropping dbg.value: expression is entry_value but "
-                         "couldn't find a physical register\n");
-    return true;
-  }
-
   assert(Variable->isValidLocationForIntrinsic(DL) &&
          "Expected inlined-at fields to agree");
   MachineInstr *NewMI = nullptr;
@@ -5953,6 +5933,41 @@ static const CallBase *FindPreallocatedCall(const Value *PreallocatedSetup) {
   llvm_unreachable("expected corresponding call to preallocated setup/arg");
 }
 
+/// If DI is a debug value with an EntryValue expression, lower it using the
+/// corresponding physical register of the associated Argument value
+/// (guaranteed to exist by the verifier).
+bool SelectionDAGBuilder::visitEntryValueDbgValue(const DbgValueInst &DI) {
+  DILocalVariable *Variable = DI.getVariable();
+  DIExpression *Expr = DI.getExpression();
+  if (!Expr->isEntryValue() || !hasSingleElement(DI.getValues()))
+    return false;
+
+  // These properties are guaranteed by the verifier.
+  Argument *Arg = cast<Argument>(DI.getValue(0));
+  assert(Arg->hasAttribute(Attribute::AttrKind::SwiftAsync));
+
+  auto ArgIt = FuncInfo.ValueMap.find(Arg);
+  if (ArgIt == FuncInfo.ValueMap.end()) {
+    LLVM_DEBUG(
+        dbgs() << "Dropping dbg.value: expression is entry_value but "
+                  "couldn't find an associated register for the Argument\n");
+    return true;
+  }
+  Register ArgVReg = ArgIt->getSecond();
+
+  for (auto [PhysReg, VirtReg] : FuncInfo.RegInfo->liveins())
+    if (ArgVReg == VirtReg || ArgVReg == PhysReg) {
+      SDDbgValue *SDV =
+          DAG.getVRegDbgValue(Variable, Expr, PhysReg, false /*IsIndidrect*/,
+                              DI.getDebugLoc(), SDNodeOrder);
+      DAG.AddDbgValue(SDV, false /*treat as dbg.declare byval parameter*/);
+      return true;
+    }
+  LLVM_DEBUG(dbgs() << "Dropping dbg.value: expression is entry_value but "
+                       "couldn't find a physical register\n");
+  return true;
+}
+
 /// Lower the call to the specified intrinsic function.
 void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
                                              unsigned Intrinsic) {
@@ -6284,6 +6299,9 @@ void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
     DIExpression *Expression = DI.getExpression();
     dropDanglingDebugInfo(Variable, Expression);
 
+    if (visitEntryValueDbgValue(DI))
+      return;
+
     if (DI.isKillLocation()) {
       handleKillDebugValue(Variable, Expression, DI.getDebugLoc(), SDNodeOrder);
       return;

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h

@@ -630,6 +630,8 @@ class SelectionDAGBuilder {
 
   void visitInlineAsm(const CallBase &Call,
                       const BasicBlock *EHPadBB = nullptr);
+
+  bool visitEntryValueDbgValue(const DbgValueInst &I);
   void visitIntrinsicCall(const CallInst &I, unsigned Intrinsic);
   void visitTargetIntrinsic(const CallInst &I, unsigned Intrinsic);
   void visitConstrainedFPIntrinsic(const ConstrainedFPIntrinsic &FPI);

llvm/test/CodeGen/AArch64/dbg-value-swift-async-non-entry-block.ll

@@ -0,0 +1,49 @@
+; RUN: llc --mtriple="aarch64-" -O0 -global-isel -stop-after=irtranslator -verify-machineinstrs %s -o - | FileCheck %s --check-prefix=AARCH
+; RUN: llc --mtriple="aarch64-" -O0 -fast-isel=false -global-isel=false -stop-after=finalize-isel %s -o - | FileCheck %s --check-prefix=AARCH
+; RUN: llc --mtriple="aarch64-" -O0 -fast-isel -stop-after=finalize-isel %s -o - | FileCheck %s --check-prefix=AARCH
+
+
+; RUN: llc --mtriple="x86_64-" -O0 -fast-isel=false -global-isel=false -stop-after=finalize-isel %s -o - | FileCheck %s --check-prefix=X86
+; RUN: llc --mtriple="x86_64-" -O0 -fast-isel -stop-after=finalize-isel %s -o - | FileCheck %s --check-prefix=X86
+
+; AARCH-NOT:  DBG_VALUE
+; AARCH:      DBG_VALUE $x22, $noreg, !{{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)
+; AARCH-NEXT: DBG_VALUE $x22, $noreg, !{{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)
+; AARCH-NOT:  DBG_VALUE
+
+; X86-NOT:  DBG_VALUE
+; X86:      DBG_VALUE $r14, $noreg, !{{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)
+; X86-NEXT: DBG_VALUE $r14, $noreg, !{{.*}}, !DIExpression(DW_OP_LLVM_entry_value, 1)
+; X86-NOT:  DBG_VALUE
+
+
+define void @foo(ptr %unused_arg, ptr swiftasync %async_arg) !dbg !6 {
+entry:
+  br label %other
+
+other:
+  call void @llvm.dbg.value(metadata ptr %async_arg, metadata !12, metadata !DIExpression(DW_OP_LLVM_entry_value, 1)), !dbg !14
+  call void @llvm.dbg.value(metadata ptr %async_arg, metadata !12, metadata !DIExpression(DW_OP_LLVM_entry_value, 1)), !dbg !14
+  call void @consume(ptr %async_arg)
+  ret void, !dbg !15
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+declare void @consume(ptr %ptr)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "x.c", directory: "/")
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 1, type: !7, isLocal: false, isDefinition: true, scopeLine: 1, unit: !0)
+!7 = !DISubroutineType(types: !8)
+!8 = !{null, !9, !9, !9}
+!9 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !10, size: 64)
+!10 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !11)
+!11 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!12 = !DILocalVariable(name: "a", scope: !6, file: !1, line: 1, type: !9)
+!14 = !DILocation(line: 1, column: 29, scope: !6)
+!15 = !DILocation(line: 1, column: 37, scope: !6)