Store a pointer to the return value in a static alloca and let the debugger use that

as the variable address for NRVO variables.

Subscribers: hiraditya, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D63361

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@363952 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/CGDebugInfo.cpp b/lib/CodeGen/CGDebugInfo.cpp
index a53ca8f5243cb8ac97d5acf95aee788d507bd2a7..dbe582cd150d89463ad8b8528dc75837a658de06 100644 (file)
--- a/lib/CodeGen/CGDebugInfo.cpp
+++ b/lib/CodeGen/CGDebugInfo.cpp
@@ -3835,7 +3835,8 @@ CGDebugInfo::EmitTypeForVarWithBlocksAttr(const VarDecl *VD,
 llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const VarDecl *VD,
                                                 llvm::Value *Storage,
                                                 llvm::Optional<unsigned> ArgNo,
-                                                CGBuilderTy &Builder) {
+                                                CGBuilderTy &Builder,
+                                                const bool UsePointerValue) {
   assert(DebugKind >= codegenoptions::LimitedDebugInfo);
   assert(!LexicalBlockStack.empty() && "Region stack mismatch, stack empty!");
   if (VD->hasAttr<NoDebugAttr>())
@@ -3940,6 +3941,16 @@ llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const VarDecl *VD,
     }
   }
 
+  // Clang stores the sret pointer provided by the caller in a static alloca.
+  // Use DW_OP_deref to tell the debugger to load the pointer and treat it as
+  // the address of the variable.
+  if (UsePointerValue) {
+    assert(std::find(Expr.begin(), Expr.end(), llvm::dwarf::DW_OP_deref) ==
+               Expr.end() &&
+           "Debug info already contains DW_OP_deref.");
+    Expr.push_back(llvm::dwarf::DW_OP_deref);
+  }
+
   // Create the descriptor for the variable.
   auto *D = ArgNo ? DBuilder.createParameterVariable(
                         Scope, Name, *ArgNo, Unit, Line, Ty,
@@ -3958,9 +3969,10 @@ llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const VarDecl *VD,
 
 llvm::DILocalVariable *
 CGDebugInfo::EmitDeclareOfAutoVariable(const VarDecl *VD, llvm::Value *Storage,
-                                       CGBuilderTy &Builder) {
+                                       CGBuilderTy &Builder,
+                                       const bool UsePointerValue) {
   assert(DebugKind >= codegenoptions::LimitedDebugInfo);
-  return EmitDeclare(VD, Storage, llvm::None, Builder);
+  return EmitDeclare(VD, Storage, llvm::None, Builder, UsePointerValue);
 }
 
 void CGDebugInfo::EmitLabel(const LabelDecl *D, CGBuilderTy &Builder) {

diff --git a/lib/CodeGen/CGDebugInfo.h b/lib/CodeGen/CGDebugInfo.h
index 054df01d97cf2b77b66474a62cf0d1693987cdf9..f0c67cdecbbe03d3b0f9744656ea91571bb35da7 100644 (file)
--- a/lib/CodeGen/CGDebugInfo.h
+++ b/lib/CodeGen/CGDebugInfo.h
@@ -422,9 +422,10 @@ public:
   /// declaration.
   /// Returns a pointer to the DILocalVariable associated with the
   /// llvm.dbg.declare, or nullptr otherwise.
-  llvm::DILocalVariable *EmitDeclareOfAutoVariable(const VarDecl *Decl,
-                                                   llvm::Value *AI,
-                                                   CGBuilderTy &Builder);
+  llvm::DILocalVariable *
+  EmitDeclareOfAutoVariable(const VarDecl *Decl, llvm::Value *AI,
+                            CGBuilderTy &Builder,
+                            const bool UsePointerValue = false);
 
   /// Emit call to \c llvm.dbg.label for an label.
   void EmitLabel(const LabelDecl *D, CGBuilderTy &Builder);
@@ -507,7 +508,8 @@ private:
   /// llvm.dbg.declare, or nullptr otherwise.
   llvm::DILocalVariable *EmitDeclare(const VarDecl *decl, llvm::Value *AI,
                                      llvm::Optional<unsigned> ArgNo,
-                                     CGBuilderTy &Builder);
+                                     CGBuilderTy &Builder,
+                                     const bool UsePointerValue = false);
 
   struct BlockByRefType {
     /// The wrapper struct used inside the __block_literal struct.

diff --git a/lib/CodeGen/CGDecl.cpp b/lib/CodeGen/CGDecl.cpp
index 233212c76bee0bce8da1480bc1ccfb7ca17f4a41..c4e0d89c83c05366a083f6a3b248026c926bc902 100644 (file)
--- a/lib/CodeGen/CGDecl.cpp
+++ b/lib/CodeGen/CGDecl.cpp
@@ -1403,12 +1403,11 @@ CodeGenFunction::EmitAutoVarAlloca(const VarDecl &D) {
       getLangOpts().OpenMP
           ? CGM.getOpenMPRuntime().getAddressOfLocalVariable(*this, &D)
           : Address::invalid();
+  bool NRVO = getLangOpts().ElideConstructors && D.isNRVOVariable();
+
   if (getLangOpts().OpenMP && OpenMPLocalAddr.isValid()) {
     address = OpenMPLocalAddr;
   } else if (Ty->isConstantSizeType()) {
-    bool NRVO = getLangOpts().ElideConstructors &&
-      D.isNRVOVariable();
-
     // If this value is an array or struct with a statically determinable
     // constant initializer, there are optimizations we can do.
     //
@@ -1561,8 +1560,16 @@ CodeGenFunction::EmitAutoVarAlloca(const VarDecl &D) {
 
   // Emit debug info for local var declaration.
   if (EmitDebugInfo && HaveInsertPoint()) {
+    Address DebugAddr = address;
+    bool UsePointerValue = NRVO && ReturnValuePointer.isValid();
     DI->setLocation(D.getLocation());
-    (void)DI->EmitDeclareOfAutoVariable(&D, address.getPointer(), Builder);
+
+    // If NRVO, use a pointer to the return address.
+    if (UsePointerValue)
+      DebugAddr = ReturnValuePointer;
+
+    (void)DI->EmitDeclareOfAutoVariable(&D, DebugAddr.getPointer(), Builder,
+                                        UsePointerValue);
   }
 
   if (D.hasAttr<AnnotateAttr>() && HaveInsertPoint())

diff --git a/lib/CodeGen/CodeGenFunction.cpp b/lib/CodeGen/CodeGenFunction.cpp
index b9573f71a3af9ea6ef36e45cd28c4d22a6a42832..581bbe5efafffd707a54b632fbcbd0a940203997 100644 (file)
--- a/lib/CodeGen/CodeGenFunction.cpp
+++ b/lib/CodeGen/CodeGenFunction.cpp
@@ -895,6 +895,13 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
     if (CurFnInfo->getReturnInfo().isSRetAfterThis())
       ++AI;
     ReturnValue = Address(&*AI, CurFnInfo->getReturnInfo().getIndirectAlign());
+    if (!CurFnInfo->getReturnInfo().getIndirectByVal()) {
+      ReturnValuePointer =
+          CreateDefaultAlignTempAlloca(Int8PtrTy, "result.ptr");
+      Builder.CreateStore(Builder.CreatePointerBitCastOrAddrSpaceCast(
+                              ReturnValue.getPointer(), Int8PtrTy),
+                          ReturnValuePointer);
+    }
   } else if (CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::InAlloca &&
              !hasScalarEvaluationKind(CurFnInfo->getReturnType())) {
     // Load the sret pointer from the argument struct and return into that.
@@ -902,6 +909,7 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
     llvm::Function::arg_iterator EI = CurFn->arg_end();
     --EI;
     llvm::Value *Addr = Builder.CreateStructGEP(nullptr, &*EI, Idx);
+    ReturnValuePointer = Address(Addr, getPointerAlign());
     Addr = Builder.CreateAlignedLoad(Addr, getPointerAlign(), "agg.result");
     ReturnValue = Address(Addr, getNaturalTypeAlignment(RetTy));
   } else {

diff --git a/lib/CodeGen/CodeGenFunction.h b/lib/CodeGen/CodeGenFunction.h
index b274f45867a804a4651015dee6d8713d382e7dc8..e95a07ce0e4482bd36674ab1ae7c06ad820ecefd 100644 (file)
--- a/lib/CodeGen/CodeGenFunction.h
+++ b/lib/CodeGen/CodeGenFunction.h
@@ -327,6 +327,10 @@ public:
   /// value. This is invalid iff the function has no return value.
   Address ReturnValue = Address::invalid();
 
+  /// ReturnValuePointer - The temporary alloca to hold a pointer to sret.
+  /// This is invalid if sret is not in use.
+  Address ReturnValuePointer = Address::invalid();
+
   /// Return true if a label was seen in the current scope.
   bool hasLabelBeenSeenInCurrentScope() const {
     if (CurLexicalScope)

diff --git a/test/CodeGen/arm64-microsoft-arguments.cpp b/test/CodeGen/arm64-microsoft-arguments.cpp
index 356bd8c974e822d1113aa0a6b37b20d493d2c482..bca7cc94b3937c76d8122185622937a762eb5fbd 100644 (file)
--- a/test/CodeGen/arm64-microsoft-arguments.cpp
+++ b/test/CodeGen/arm64-microsoft-arguments.cpp
@@ -43,7 +43,7 @@ S3 f3() {
 // Pass and return aggregate (of size < 16 bytes) with non-trivial destructor.
 // Passed directly but returned indirectly.
 // CHECK: define {{.*}} void {{.*}}f4{{.*}}(%struct.S4* inreg noalias sret %agg.result)
-// CHECK: call void {{.*}}func4{{.*}}(%struct.S4* inreg sret %agg.result, [2 x i64] %4)
+// CHECK: call void {{.*}}func4{{.*}}(%struct.S4* inreg sret %agg.result, [2 x i64] %5)
 struct S4 {
   int a[3];
   ~S4();
@@ -57,7 +57,7 @@ S4 f4() {
 
 // Pass and return from instance method called from instance method.
 // CHECK: define {{.*}} void @{{.*}}bar@Q1{{.*}}(%class.Q1* %this, %class.P1* inreg noalias sret %agg.result)
-// CHECK: call void {{.*}}foo@P1{{.*}}(%class.P1* %ref.tmp, %class.P1* inreg sret %agg.result, i8 %0)
+// CHECK: call void {{.*}}foo@P1{{.*}}(%class.P1* %ref.tmp, %class.P1* inreg sret %agg.result, i8 %1)
 
 class P1 {
 public:

diff --git a/test/CodeGenCXX/conditional-gnu-ext.cpp b/test/CodeGenCXX/conditional-gnu-ext.cpp
index b073e0cc66a724f3d6cde96adff166cef8501574..613dd65ee7c963a1da078d9fcb0eb557bb5f9be4 100644 (file)
--- a/test/CodeGenCXX/conditional-gnu-ext.cpp
+++ b/test/CodeGenCXX/conditional-gnu-ext.cpp
@@ -79,7 +79,7 @@ namespace test3 {
   B test0(B &x) {
     // CHECK-LABEL:    define void @_ZN5test35test0ERNS_1BE(
     // CHECK:      [[X:%.*]] = alloca [[B:%.*]]*,
-    // CHECK-NEXT: store [[B]]* {{%.*}}, [[B]]** [[X]]
+    // CHECK:      store [[B]]* {{%.*}}, [[B]]** [[X]]
     // CHECK-NEXT: [[T0:%.*]] = load [[B]]*, [[B]]** [[X]]
     // CHECK-NEXT: [[BOOL:%.*]] = call zeroext i1 @_ZN5test31BcvbEv([[B]]* [[T0]])
     // CHECK-NEXT: br i1 [[BOOL]]
@@ -94,7 +94,7 @@ namespace test3 {
   B test1() {
     // CHECK-LABEL:    define void @_ZN5test35test1Ev(
     // CHECK:      [[TEMP:%.*]] = alloca [[B]],
-    // CHECK-NEXT: call  void @_ZN5test312test1_helperEv([[B]]* sret [[TEMP]])
+    // CHECK:      call  void @_ZN5test312test1_helperEv([[B]]* sret [[TEMP]])
     // CHECK-NEXT: [[BOOL:%.*]] = call zeroext i1 @_ZN5test31BcvbEv([[B]]* [[TEMP]])
     // CHECK-NEXT: br i1 [[BOOL]]
     // CHECK:      call void @_ZN5test31BC1ERKS0_([[B]]* [[RESULT:%.*]], [[B]]* dereferenceable({{[0-9]+}}) [[TEMP]])
@@ -111,7 +111,7 @@ namespace test3 {
   A test2(B &x) {
     // CHECK-LABEL:    define void @_ZN5test35test2ERNS_1BE(
     // CHECK:      [[X:%.*]] = alloca [[B]]*,
-    // CHECK-NEXT: store [[B]]* {{%.*}}, [[B]]** [[X]]
+    // CHECK:      store [[B]]* {{%.*}}, [[B]]** [[X]]
     // CHECK-NEXT: [[T0:%.*]] = load [[B]]*, [[B]]** [[X]]
     // CHECK-NEXT: [[BOOL:%.*]] = call zeroext i1 @_ZN5test31BcvbEv([[B]]* [[T0]])
     // CHECK-NEXT: br i1 [[BOOL]]
@@ -126,7 +126,7 @@ namespace test3 {
   A test3() {
     // CHECK-LABEL:    define void @_ZN5test35test3Ev(
     // CHECK:      [[TEMP:%.*]] = alloca [[B]],
-    // CHECK-NEXT: call  void @_ZN5test312test3_helperEv([[B]]* sret [[TEMP]])
+    // CHECK:      call  void @_ZN5test312test3_helperEv([[B]]* sret [[TEMP]])
     // CHECK-NEXT: [[BOOL:%.*]] = call zeroext i1 @_ZN5test31BcvbEv([[B]]* [[TEMP]])
     // CHECK-NEXT: br i1 [[BOOL]]
     // CHECK:      call void @_ZN5test31BcvNS_1AEEv([[A]]* sret [[RESULT:%.*]], [[B]]* [[TEMP]])

diff --git a/test/CodeGenCXX/debug-info-nrvo.cpp b/test/CodeGenCXX/debug-info-nrvo.cpp
new file mode 100644 (file)
index 0000000..a03571a
--- /dev/null
+++ b/test/CodeGenCXX/debug-info-nrvo.cpp
@@ -0,0 +1,28 @@
+// RUN: %clangxx -target x86_64-unknown-unknown -g %s -emit-llvm -S -o - | FileCheck %s
+// RUN: %clangxx -target x86_64-unknown-unknown -g -fno-elide-constructors %s -emit-llvm -S -o - | FileCheck %s -check-prefix=NOELIDE
+struct Foo {
+  Foo() = default;
+  Foo(Foo &&other) { x = other.x; }
+  int x;
+};
+void some_function(int);
+Foo getFoo() {
+  Foo foo;
+  foo.x = 41;
+  some_function(foo.x);
+  return foo;
+}
+
+int main() {
+  Foo bar = getFoo();
+  return bar.x;
+}
+
+// Check that NRVO variables are stored as a pointer with deref if they are
+// stored in the return register.
+
+// CHECK: %result.ptr = alloca i8*, align 8
+// CHECK: call void @llvm.dbg.declare(metadata i8** %result.ptr,
+// CHECK-SAME: metadata !DIExpression(DW_OP_deref)
+// NOELIDE: call void @llvm.dbg.declare(metadata %struct.Foo* %foo,
+// NOELIDE-SAME:                        metadata !DIExpression()

diff --git a/test/CodeGenCXX/lambda-expressions.cpp b/test/CodeGenCXX/lambda-expressions.cpp
index 2c625daaf831b27cadd34b3ec1a468f388e418bf..566132ad64e303e8fd9518d85821d0ff99808cbe 100644 (file)
--- a/test/CodeGenCXX/lambda-expressions.cpp
+++ b/test/CodeGenCXX/lambda-expressions.cpp
@@ -195,7 +195,6 @@ namespace pr28595 {
 // CHECK-NEXT: ret i32
 
 // CHECK-LABEL: define internal void @"_ZZ1hvEN4$_118__invokeEv"(%struct.A* noalias sret %agg.result) {{.*}} {
-// CHECK-NOT: =
 // CHECK: call void @"_ZZ1hvENK4$_11clEv"(%struct.A* sret %agg.result,
 // CHECK-NEXT: ret void
 struct A { ~A(); };

diff --git a/test/CodeGenObjC/objc-non-trivial-struct-nrvo.m b/test/CodeGenObjC/objc-non-trivial-struct-nrvo.m
index 798aba248941ed029f55a988b6ebe1131d1d5dab..53ff433989e29b9934e30d3460a6785a26f0333d 100644 (file)
--- a/test/CodeGenObjC/objc-non-trivial-struct-nrvo.m
+++ b/test/CodeGenObjC/objc-non-trivial-struct-nrvo.m
@@ -38,7 +38,6 @@ Trivial testTrivial(void) {
 void func1(TrivialBig *);
 
 // CHECK: define void @testTrivialBig(%[[STRUCT_TRIVIALBIG]]* noalias sret %[[AGG_RESULT:.*]])
-// CHECK-NOT: alloca
 // CHECK: call void @func1(%[[STRUCT_TRIVIALBIG]]* %[[AGG_RESULT]])
 // CHECK-NEXT: ret void